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| -rw-r--r-- | doc/latex/.gitignore | 2 | ||||
| -rw-r--r-- | doc/latex/Makefile | 66 | ||||
| -rw-r--r-- | doc/latex/src/16bit.tex | 868 | ||||
| -rw-r--r-- | doc/latex/src/32bit.tex | 539 | ||||
| -rw-r--r-- | doc/latex/src/64bit.tex | 204 | ||||
| -rw-r--r-- | doc/latex/src/changelog.tex | 2304 | ||||
| -rw-r--r-- | doc/latex/src/contact.tex | 111 | ||||
| -rw-r--r-- | doc/latex/src/directive.tex | 541 | ||||
| -rw-r--r-- | doc/latex/src/idxconf.ist | 9 | ||||
| -rw-r--r-- | doc/latex/src/inslist.tex | 14 | ||||
| -rw-r--r-- | doc/latex/src/intro.tex | 55 | ||||
| -rw-r--r-- | doc/latex/src/language.tex | 945 | ||||
| -rw-r--r-- | doc/latex/src/macropkg.tex | 127 | ||||
| -rw-r--r-- | doc/latex/src/mixsize.tex | 185 | ||||
| -rw-r--r-- | doc/latex/src/nasm.tex | 163 | ||||
| -rw-r--r-- | doc/latex/src/nasmlogo.eps | 212 | ||||
| -rw-r--r-- | doc/latex/src/ndisasm.tex | 174 | ||||
| -rw-r--r-- | doc/latex/src/outfmt.tex | 1606 | ||||
| -rw-r--r-- | doc/latex/src/preproc.tex | 2400 | ||||
| -rw-r--r-- | doc/latex/src/running.tex | 902 | ||||
| -rw-r--r-- | doc/latex/src/source.tex | 53 | ||||
| -rw-r--r-- | doc/latex/src/trouble.tex | 114 | ||||
| -rw-r--r-- | doc/latex/src/version.tex | 4 |
23 files changed, 11598 insertions, 0 deletions
diff --git a/doc/latex/.gitignore b/doc/latex/.gitignore new file mode 100644 index 00000000..4f265ac2 --- /dev/null +++ b/doc/latex/.gitignore @@ -0,0 +1,2 @@ +.git-ignore/ +*.swp diff --git a/doc/latex/Makefile b/doc/latex/Makefile new file mode 100644 index 00000000..afbe73ad --- /dev/null +++ b/doc/latex/Makefile @@ -0,0 +1,66 @@ +.PHONY: all .FORCE +.DEFAULT_GOAL := all + +ifeq ($(strip $(V)),) + E := @echo + Q := @ +else + E := @\# + Q := +endif + +export E Q + +define msg-gen + $(E) " GEN " $(1) +endef + +define msg-clean + $(E) " CLEAN " $(1) +endef + +RM ?= rm -f +XELATEX ?= xelatex +XELATEX-OPTS ?= -output-driver="xdvipdfmx -V 3" -8bit + +tex-d += src/16bit.tex +tex-d += src/32bit.tex +tex-d += src/64bit.tex +tex-d += src/changelog.tex +tex-d += src/contact.tex +tex-d += src/directive.tex +tex-d += src/idxconf.ist +tex-d += src/inslist.tex +tex-d += src/intro.tex +tex-d += src/language.tex +tex-d += src/macropkg.tex +tex-d += src/mixsize.tex +tex-d += src/nasmlogo.eps +tex-d += src/ndisasm.tex +tex-d += src/outfmt.tex +tex-d += src/preproc.tex +tex-d += src/running.tex +tex-d += src/source.tex +tex-d += src/trouble.tex +tex-d += src/version.tex +tex-y += src/nasm.tex + +$(tex-y): $(tex-d) + @true + +nasm.pdf: $(tex-y) .FORCE + $(call msg-gen,$@) + $(Q) $(XELATEX) $(XELATEX-OPTS) $^ + $(Q) $(XELATEX) $(XELATEX-OPTS) $^ +all-y += nasm.pdf + +# Default target +all: $(all-y) + +clean: + $(call msg-clean,nasm) + $(Q) $(RM) ./nasm.aux ./nasm.idx ./nasm.ilg ./nasm.ind ./nasm.log + $(Q) $(RM) ./nasm.out ./nasm.pdf ./nasm.toc + +# Disable implicit rules in _this_ Makefile. +.SUFFIXES: diff --git a/doc/latex/src/16bit.tex b/doc/latex/src/16bit.tex new file mode 100644 index 00000000..79bebcb9 --- /dev/null +++ b/doc/latex/src/16bit.tex @@ -0,0 +1,868 @@ +% +% vim: ts=4 sw=4 et +% +\xchapter{16bit}{Writing 16-bit Code (DOS, Windows 3/3.1)} + +This chapter attempts to cover some of the common issues encountered +when writing 16-bit code to run under \code{MS-DOS} or \code{Windows 3.x}. +It covers how to link programs to produce \code{.EXE} or \code{.COM} files, +how to write \code{.SYS} device drivers, and how to interface assembly +language code with 16-bit C compilers and with Borland Pascal. + +\xsection{exefiles}{Producing \codeindex{.EXE} Files} + +Any large program written under DOS needs to be built as a \code{.EXE} +file: only \code{.EXE} files have the necessary internal structure +required to span more than one 64K segment. \textindex{Windows} programs, +also, have to be built as \code{.EXE} files, since Windows does not +support the \code{.COM} format. + +In general, you generate \code{.EXE} files by using the \code{obj} output +format to produce one or more \codeindex{.OBJ} files, and then linking +them together using a linker. However, NASM also supports the direct +generation of simple DOS \code{.EXE} files using the \code{bin} output +format (by using \code{DB} and \code{DW} to construct the \code{.EXE} file +header), and a macro package is supplied to do this. Thanks to +Yann Guidon for contributing the code for this. + +NASM may also support \code{.EXE} natively as another output format in +future releases. + +\xsubsection{objexe}{Using the \code{obj} Format To Generate \code{.EXE} Files} + +This section describes the usual method of generating \code{.EXE} files +by linking \code{.OBJ} files together. + +Most 16-bit programming language packages come with a suitable +linker; if you have none of these, there is a free linker called +\textindex{VALX}\index{linker!VALX}, available as a part of +CC386 compiler on \href{http://ladsoft.tripod.com/cc386\_compiler.html} +{ladsoft.tripod.com}. + +There is another `free' linker (though this one doesn't come with +sources) called \textindex{FREELINK}\index{linker!FREELINK}, available +from \href{http://www.pcorner.com/tpc/old/3-101.html}{www.pcorner.com}. + +A third, \textindex{djlink}, written by DJ Delorie, is available at +\href{http://www.delorie.com/djgpp/16bit/djlink/}{www.delorie.com}. + +A fourth linker, \textindex{ALINK}\index{linker!ALINK}, written by +Anthony A.J. Williams, is available at \href{http://alink.sourceforge.net} +{alink.sourceforge.net}. + +When linking several \code{.OBJ} files into a \code{.EXE} file, you should +ensure that exactly one of them has a start point defined (using the +\index{program entry point}\codeindex{..start} special symbol defined by the +\code{obj} format: see \nref{dotdotstart}). If no module defines a start +point, the linker will not know what value to give the entry-point +field in the output file header; if more than one defines a start +point, the linker will not know \emph{which} value to use. + +An example of a NASM source file which can be assembled to a +\code{.OBJ} file and linked on its own to a \code{.EXE} is given here. It +demonstrates the basic principles of defining a stack, initialising +the segment registers, and declaring a start point. This file is +also provided in the \index{test subdirectory}\code{test} subdirectory of +the NASM archives, under the name \code{objexe.asm}. + +\begin{lstlisting} +segment code + +..start: + mov ax,data + mov ds,ax + mov ax,stack + mov ss,ax + mov sp,stacktop +\end{lstlisting} + +This initial piece of code sets up \code{DS} to point to the data +segment, and initializes \code{SS} and \code{SP} to point to the top of +the provided stack. Notice that interrupts are implicitly disabled +for one instruction after a move into \code{SS}, precisely for this +situation, so that there's no chance of an interrupt occurring +between the loads of \code{SS} and \code{SP} and not having a stack to +execute on. + +Note also that the special symbol \code{..start} is defined at the +beginning of this code, which means that will be the entry point +into the resulting executable file. + +\begin{lstlisting} + mov dx,hello + mov ah,9 + int 0x21 +\end{lstlisting} + +The above is the main program: load \code{DS:DX} with a pointer to the +greeting message (\code{hello} is implicitly relative to the segment +\code{data}, which was loaded into \code{DS} in the setup code, so the +full pointer is valid), and call the DOS print-string function. + +\begin{lstlisting} + mov ax,0x4c00 + int 0x21 +\end{lstlisting} + +This terminates the program using another DOS system call. + +\begin{lstlisting} +segment data + +hello: db 'hello, world', 13, 10, '$' +\end{lstlisting} + +The data segment contains the string we want to display. + +\begin{lstlisting} +segment stack stack + resb 64 +stacktop: +\end{lstlisting} + +The above code declares a stack segment containing 64 bytes of +uninitialized stack space, and points \code{stacktop} at the top of it. +The directive \code{segment stack stack} defines a segment \emph{called} +\code{stack}, and also of \emph{type} \code{STACK}. The latter is not +necessary to the correct running of the program, but linkers are +likely to issue warnings or errors if your program has no segment of +type \code{STACK}. + +The above file, when assembled into a \code{.OBJ} file, will link on +its own to a valid \code{.EXE} file, which when run will print `hello, +world' and then exit. + +\xsubsection{binexe}{Using the \code{bin} Format To Generate \code{.EXE} Files} + +The \code{.EXE} file format is simple enough that it's possible to +build a \code{.EXE} file by writing a pure-binary program and sticking +a 32-byte header on the front. This header is simple enough that it +can be generated using \code{DB} and \code{DW} commands by NASM itself, +so that you can use the \code{bin} output format to directly generate +\code{.EXE} files. + +Included in the NASM archives, in the \index{misc subdirectory}\code{misc} +subdirectory, is a file \codeindex{exebin.mac} of macros. It defines three +macros: \codeindex{EXE\_begin}, \codeindex{EXE\_stack} and +\codeindex{EXE\_end}. + +To produce a \code{.EXE} file using this method, you should start by +using \code{\%include} to load the \code{exebin.mac} macro package into +your source file. You should then issue the \code{EXE\_begin} macro call +(which takes no arguments) to generate the file header data. Then +write code as normal for the \code{bin} format - you can use all three +standard sections \code{.text}, \code{.data} and \code{.bss}. At the end of +the file you should call the \code{EXE\_end} macro (again, no arguments), +which defines some symbols to mark section sizes, and these symbols +are referred to in the header code generated by \code{EXE\_begin}. + +In this model, the code you end up writing starts at \code{0x100}, just +like a \code{.COM} file - in fact, if you strip off the 32-byte header +from the resulting \code{.EXE} file, you will have a valid \code{.COM} +program. All the segment bases are the same, so you are limited to a +64K program, again just like a \code{.COM} file. Note that an \code{ORG} +directive is issued by the \code{EXE\_begin} macro, so you should not +explicitly issue one of your own. + +You can't directly refer to your segment base value, unfortunately, +since this would require a relocation in the header, and things +would get a lot more complicated. So you should get your segment +base by copying it out of \code{CS} instead. + +On entry to your \code{.EXE} file, \code{SS:SP} are already set up to +point to the top of a 2Kb stack. You can adjust the default stack +size of 2Kb by calling the \code{EXE\_stack} macro. For example, to +change the stack size of your program to 64 bytes, you would call +\code{EXE\_stack 64}. + +A sample program which generates a \code{.EXE} file in this way is +given in the \code{test} subdirectory of the NASM archive, as +\code{binexe.asm}. + +\xsection{comfiles}{Producing \codeindex{.COM} Files} + +While large DOS programs must be written as \code{.EXE} files, small +ones are often better written as \code{.COM} files. \code{.COM} files are +pure binary, and therefore most easily produced using the \code{bin} +output format. + +\xsubsection{combinfmt}{Using the \code{bin} Format To Generate \code{.COM} Files} + +\code{.COM} files expect to be loaded at offset \code{100h} into their +segment (though the segment may change). Execution then begins at +\indexcode{ORG}\code{100h}, i.e. right at the start of the program. +So to write a \code{.COM} program, you would create a source file +looking like + +\begin{lstlisting} + org 100h + +section .text +start: + ; put your code here + +section .data + ; put data items here + +section .bss + ; put uninitialized data here +\end{lstlisting} + +The \code{bin} format puts the \code{.text} section first in the file, +so you can declare data or BSS items before beginning to write code if +you want to and the code will still end up at the front of the file +where it belongs. + +The BSS (uninitialized data) section does not take up space in the +\code{.COM} file itself: instead, addresses of BSS items are resolved +to point at space beyond the end of the file, on the grounds that +this will be free memory when the program is run. Therefore you +should not rely on your BSS being initialized to all zeros when you +run. + +To assemble the above program, you should use a command line like + +\begin{lstlisting} +nasm myprog.asm -fbin -o myprog.com +\end{lstlisting} + +The \code{bin} format would produce a file called \code{myprog} if no +explicit output file name were specified, so you have to override it +and give the desired file name. + +\xsubsection{comobjfmt}{Using the \code{obj} Format To Generate \code{.COM} Files} + +If you are writing a \code{.COM} program as more than one module, you +may wish to assemble several \code{.OBJ} files and link them together +into a \code{.COM} program. You can do this, provided you have a linker +capable of outputting \code{.COM} files directly (\textindex{TLINK} does this), +or alternatively a converter program such as \codeindex{EXE2BIN} to +transform the \code{.EXE} file output from the linker into a \code{.COM} +file. + +If you do this, you need to take care of several things: + +\begin{itemize} + \item{The first object file containing code should start its code + segment with a line like \code{RESB 100h}. This is to ensure + that the code begins at offset \code{100h} relative to the beginning + of the code segment, so that the linker or converter program does + not have to adjust address references within the file when generating + the \code{.COM} file. Other assemblers use an \codeindex{ORG} directive + for this purpose, but \code{ORG} in NASM is a format-specific directive + to the \code{bin} output format, and does not mean the same thing as + it does in MASM-compatible assemblers.} + \item{You don't need to define a stack segment.} + \item{All your segments should be in the same group, so that every time + your code or data references a symbol offset, all offsets are + relative to the same segment base. This is because, when a \code{.COM} + file is loaded, all the segment registers contain the same value.} +\end{itemize} + +\xsection{sysfiles}{Producing \codeindex{.SYS} Files} + +\textindex{MS-DOS device drivers} - \code{.SYS} files - are pure binary files, +similar to \code{.COM} files, except that they start at origin zero +rather than \code{100h}. Therefore, if you are writing a device driver +using the \code{bin} format, you do not need the \code{ORG} directive, +since the default origin for \code{bin} is zero. Similarly, if you are +using \code{obj}, you do not need the \code{RESB 100h} at the start of +your code segment. + +\code{.SYS} files start with a header structure, containing pointers to +the various routines inside the driver which do the work. This +structure should be defined at the start of the code segment, even +though it is not actually code. + +For more information on the format of \code{.SYS} files, and the data +which has to go in the header structure, a list of books is given in +the Frequently Asked Questions list for the newsgroup +\href{news:comp.os.msdos.programmer}{comp.os.msdos.programmer}. + +\xsection{16c}{Interfacing to 16-bit C Programs} + +This section covers the basics of writing assembly routines that +call, or are called from, C programs. To do this, you would +typically write an assembly module as a \code{.OBJ} file, and link it +with your C modules to produce a \textindex{mixed-language program}. + +\xsubsection{16cunder}{External Symbol Names} + +\index{C symbol names}\index{underscore!in C symbols}C compilers have the +convention that the names of all global symbols (functions or data) +they define are formed by prefixing an underscore to the name as it +appears in the C program. So, for example, the function a C +programmer thinks of as \code{printf} appears to an assembly language +programmer as \code{\_printf}. This means that in your assembly +programs, you can define symbols without a leading underscore, and +not have to worry about name clashes with C symbols. + +If you find the underscores inconvenient, you can define macros to +replace the \code{GLOBAL} and \code{EXTERN} directives as follows: + +\begin{lstlisting} +%macro cglobal 1 + global _%1 + %define %1 _%1 +%endmacro + +%macro cextern 1 + extern _%1 + %define %1 _%1 +%endmacro +\end{lstlisting} + +(These forms of the macros only take one argument at a time; a +\code{\%rep} construct could solve this.) + +If you then declare an external like this: + +\begin{lstlisting} +cextern printf +\end{lstlisting} + +then the macro will expand it as + +\begin{lstlisting} +extern _printf +%define printf _printf +\end{lstlisting} + +Thereafter, you can reference \code{printf} as if it was a symbol, and +the preprocessor will put the leading underscore on where necessary. + +The \code{cglobal} macro works similarly. You must use \code{cglobal} +before defining the symbol in question, but you would have had to do +that anyway if you used \code{GLOBAL}. + +Also see \nref{opt-pfix}. + +\xsubsection{16cmodels}{\textindexlc{Memory Models}} + +NASM contains no mechanism to support the various C memory models +directly; you have to keep track yourself of which one you are +writing for. This means you have to keep track of the following +things: + +\begin{itemize} + \item{In models using a single code segment (tiny, small and compact), + functions are near. This means that function pointers, when stored + in data segments or pushed on the stack as function arguments, are + 16 bits long and contain only an offset field (the \code{CS} register + never changes its value, and always gives the segment part of the + full function address), and that functions are called using ordinary + near \code{CALL} instructions and return using \code{RETN} (which, in + NASM, is synonymous with \code{RET} anyway). This means both that you + should write your own routines to return with \code{RETN}, and that you + should call external C routines with near \code{CALL} instructions.} + + \item{In models using more than one code segment (medium, large and + huge), functions are far. This means that function pointers are 32 + bits long (consisting of a 16-bit offset followed by a 16-bit + segment), and that functions are called using \code{CALL FAR} (or + \code{CALL seg:offset}) and return using \code{RETF}. Again, you should + therefore write your own routines to return with \code{RETF} and use + \code{CALL FAR} to call external routines.} + + \item{In models using a single data segment (tiny, small and medium), + data pointers are 16 bits long, containing only an offset field (the + \code{DS} register doesn't change its value, and always gives the + segment part of the full data item address).} + + \item{In models using more than one data segment (compact, large and + huge), data pointers are 32 bits long, consisting of a 16-bit offset + followed by a 16-bit segment. You should still be careful not to + modify \code{DS} in your routines without restoring it afterwards, but + \code{ES} is free for you to use to access the contents of 32-bit data + pointers you are passed.} + + \item{The huge memory model allows single data items to exceed 64K in + size. In all other memory models, you can access the whole of a data + item just by doing arithmetic on the offset field of the pointer you + are given, whether a segment field is present or not; in huge model, + you have to be more careful of your pointer arithmetic.} + + \item{In most memory models, there is a \emph{default} data segment, whose + segment address is kept in \code{DS} throughout the program. This data + segment is typically the same segment as the stack, kept in \code{SS}, + so that functions' local variables (which are stored on the stack) + and global data items can both be accessed easily without changing + \code{DS}. Particularly large data items are typically stored in other + segments. However, some memory models (though not the standard + ones, usually) allow the assumption that \code{SS} and \code{DS} hold the + same value to be removed. Be careful about functions' local + variables in this latter case.} +\end{itemize} + +In models with a single code segment, the segment is called \codeindex{\_TEXT}, +so your code segment must also go by this name in order to be linked into the +same place as the main code segment. In models with a single data segment, +or with a default data segment, it is called \codeindex{\_DATA}. + +\xsubsection{16cfunc}{Function Definitions and Function Calls} + +\index{functions!C calling convention}The \textindex{C calling convention} +in 16-bit programs is as follows. In the following description, the +words \emph{caller} and \emph{callee} are used to denote the function +doing the calling and the function which gets called. + +\begin{itemize} + \item{The caller pushes the function's parameters on the stack, one + after another, in reverse order (right to left, so that the first + argument specified to the function is pushed last).} + + \item{The caller then executes a \code{CALL} instruction to pass control + to the callee. This \code{CALL} is either near or far depending on the + memory model.} + + \item{The callee receives control, and typically (although this is not + actually necessary, in functions which do not need to access their + parameters) starts by saving the value of \code{SP} in \code{BP} so as to + be able to use \code{BP} as a base pointer to find its parameters on + the stack. However, the caller was probably doing this too, so part + of the calling convention states that \code{BP} must be preserved by + any C function. Hence the callee, if it is going to set up \code{BP} as + a \emph{\textindex{frame pointer}}, must push the previous value first.} + + \item{The callee may then access its parameters relative to \code{BP}. + The word at \code{[BP]} holds the previous value of \code{BP} as it was + pushed; the next word, at \code{[BP+2]}, holds the offset part of the + return address, pushed implicitly by \code{CALL}. In a small-model + (near) function, the parameters start after that, at \code{[BP+4]}; in + a large-model (far) function, the segment part of the return address + lives at \code{[BP+4]}, and the parameters begin at \code{[BP+6]}. The + leftmost parameter of the function, since it was pushed last, is + accessible at this offset from \code{BP}; the others follow, at + successively greater offsets. Thus, in a function such as \code{printf} + which takes a variable number of parameters, the pushing of the + parameters in reverse order means that the function knows where to + find its first parameter, which tells it the number and type of the + remaining ones.} + + \item{The callee may also wish to decrease \code{SP} further, so as to + allocate space on the stack for local variables, which will then be + accessible at negative offsets from \code{BP}.} + + \item{The callee, if it wishes to return a value to the caller, should + leave the value in \code{AL}, \code{AX} or \code{DX:AX} depending + on the size of the value. Floating-point results are sometimes + (depending on the compiler) returned in \code{ST0}.} + + \item{Once the callee has finished processing, it restores \code{SP} from + \code{BP} if it had allocated local stack space, then pops the previous + value of \code{BP}, and returns via \code{RETN} or \code{RETF} depending on + memory model.} + + \item{When the caller regains control from the callee, the function + parameters are still on the stack, so it typically adds an immediate + constant to \code{SP} to remove them (instead of executing a number of + slow \code{POP} instructions). Thus, if a function is accidentally + called with the wrong number of parameters due to a prototype + mismatch, the stack will still be returned to a sensible state since + the caller, which \emph{knows} how many parameters it pushed, does the + removing.} +\end{itemize} + +It is instructive to compare this calling convention with that for +Pascal programs (described in \nref{16bpfunc}). Pascal has +a simpler convention, since no functions have variable numbers of parameters. +Therefore the callee knows how many parameters it should have been +passed, and is able to deallocate them from the stack itself by +passing an immediate argument to the \code{RET} or \code{RETF} +instruction, so the caller does not have to do it. Also, the +parameters are pushed in left-to-right order, not right-to-left, +which means that a compiler can give better guarantees about +sequence points without performance suffering. + +Thus, you would define a function in C style in the following way. +The following example is for small model: + +\begin{lstlisting} +global _myfunc + +_myfunc: + push bp + mov bp,sp + sub sp,0x40 ; 64 bytes of local stack space + mov bx,[bp+4] ; first parameter to function + + ; some more code + + mov sp,bp ; undo "sub sp,0x40" above + pop bp + ret +\end{lstlisting} + +For a large-model function, you would replace \code{RET} by \code{RETF}, +and look for the first parameter at \code{[BP+6]} instead of +\code{[BP+4]}. Of course, if one of the parameters is a pointer, then +the offsets of \emph{subsequent} parameters will change depending on +the memory model as well: far pointers take up four bytes on the +stack when passed as a parameter, whereas near pointers take up two. + +At the other end of the process, to call a C function from your +assembly code, you would do something like this: + +\begin{lstlisting} +extern _printf + ; and then, further down... + + push word [myint] ; one of my integer variables + push word mystring ; pointer into my data segment + call _printf + add sp,byte 4 ; `byte' saves space + + ; then those data items... +segment _DATA + +myint dw 1234 +mystring db 'This number -> %d <- should be 1234',10,0 +\end{lstlisting} + +This piece of code is the small-model assembly equivalent of the C +code + +\begin{lstlisting} + int myint = 1234; + printf("This number -> %d <- should be 1234\n", myint); +\end{lstlisting} + +In large model, the function-call code might look more like this. In +this example, it is assumed that \code{DS} already holds the segment +base of the segment \code{\_DATA}. If not, you would have to initialize +it first. + +\begin{lstlisting} + push word [myint] + push word seg mystring ; Now push the segment, and... + push word mystring ; ... offset of "mystring" + call far _printf + add sp,byte 6 +\end{lstlisting} + +The integer value still takes up one word on the stack, since large +model does not affect the size of the \code{int} data type. The first +argument (pushed last) to \code{printf}, however, is a data pointer, +and therefore has to contain a segment and offset part. The segment +should be stored second in memory, and therefore must be pushed +first. (Of course, \code{PUSH DS} would have been a shorter instruction +than \code{PUSH WORD SEG mystring}, if \code{DS} was set up as the above +example assumed.) Then the actual call becomes a far call, since +functions expect far calls in large model; and \code{SP} has to be +increased by 6 rather than 4 afterwards to make up for the extra +word of parameters. + +\xsubsection{16cdata}{Accessing Data Items} + +To get at the contents of C variables, or to declare variables which +C can access, you need only declare the names as \code{GLOBAL} or +\code{EXTERN}. (Again, the names require leading underscores, as stated +in \nref{16cunder}.) Thus, a C variable declared as \code{int i} +can be accessed from assembler as + +\begin{lstlisting} +extern _i + + mov ax,[_i] +\end{lstlisting} + +And to declare your own integer variable which C programs can access +as \code{extern int j}, you do this (making sure you are assembling in +the \code{\_DATA} segment, if necessary): + +\begin{lstlisting} +global _j + +_j dw 0 +\end{lstlisting} + +To access a C array, you need to know the size of the components of +the array. For example, \code{int} variables are two bytes long, so if +a C program declares an array as \code{int a[10]}, you can access +\code{a[3]} by coding \code{mov ax,[\_a+6]}. (The byte offset 6 is obtained +by multiplying the desired array index, 3, by the size of the array +element, 2.) The sizes of the C base types in 16-bit compilers are: +1 for \code{char}, 2 for \code{short} and \code{int}, 4 for \code{long} +and \code{float}, and 8 for \code{double}. + +To access a C \textindex{data structure}, you need to know the offset from +the base of the structure to the field you are interested in. You +can either do this by converting the C structure definition into a +NASM structure definition (using \codeindex{STRUC}), or by calculating the +one offset and using just that. + +To do either of these, you should read your C compiler's manual to +find out how it organizes data structures. NASM gives no special +alignment to structure members in its own \code{STRUC} macro, so you +have to specify alignment yourself if the C compiler generates it. +Typically, you might find that a structure like + +\begin{lstlisting} +struct { + char c; + int i; +} foo; +\end{lstlisting} + +might be four bytes long rather than three, since the \code{int} field +would be aligned to a two-byte boundary. However, this sort of +feature tends to be a configurable option in the C compiler, either +using command-line options or \code{\#pragma} lines, so you have to find +out how your own compiler does it. + +\xsubsection{16cmacro}{\codeindex{c16.mac}: Helper Macros for the 16-bit C Interface} + +Included in the NASM archives, in the \index{misc subdirectory}\code{misc} +directory, is a file \code{c16.mac} of macros. It defines three macros: +\codeindex{proc}, \codeindex{arg} and \codeindex{endproc}. These are intended +to be used for C-style procedure definitions, and they automate a lot of +the work involved in keeping track of the calling convention. + +(An alternative, TASM compatible form of \code{arg} is also now built +into NASM's preprocessor. See \nref{stackrel} for details.) + +An example of an assembly function using the macro set is given +here: + +\begin{lstlisting} +proc _nearproc +%$i arg +%$j arg + mov ax,[bp + %$i] + mov bx,[bp + %$j] + add ax,[bx] +endproc +\end{lstlisting} + +This defines \code{\_nearproc} to be a procedure taking two arguments, +the first (\code{i}) an integer and the second (\code{j}) a pointer to an +integer. It returns \code{i + *j}. + +Note that the \code{arg} macro has an \code{EQU} as the first line of its +expansion, and since the label before the macro call gets prepended +to the first line of the expanded macro, the \code{EQU} works, defining +\code{\%\$i} to be an offset from \code{BP}. A context-local variable is +used, local to the context pushed by the \code{proc} macro and popped +by the \code{endproc} macro, so that the same argument name can be used +in later procedures. Of course, you don't \emph{have} to do that. + +The macro set produces code for near functions (tiny, small and +compact-model code) by default. You can have it generate far +functions (medium, large and huge-model code) by means of coding +\indexcode{FARCODE}\code{\%define FARCODE}. This changes the kind of +return instruction generated by \code{endproc}, and also changes the +starting point for the argument offsets. The macro set contains no +intrinsic dependency on whether data pointers are far or not. + +\code{arg} can take an optional parameter, giving the size of the +argument. If no size is given, 2 is assumed, since it is likely that +many function parameters will be of type \code{int}. + +The large-model equivalent of the above function would look like this: + +\begin{lstlisting} +%define FARCODE + +proc _farproc +%$i arg +%$j arg 4 + mov ax,[bp + %$i] + mov bx,[bp + %$j] + mov es,[bp + %$j + 2] + add ax,[bx] +endproc +\end{lstlisting} + +This makes use of the argument to the \code{arg} macro to define a +parameter of size 4, because \code{j} is now a far pointer. When we +load from \code{j}, we must load a segment and an offset. + +\xsection{16bp}{Interfacing to \textindex{Borland Pascal} Programs} + +Interfacing to Borland Pascal programs is similar in concept to +interfacing to 16-bit C programs. The differences are: + +\begin{itemize} + \item{The leading underscore required for interfacing to C programs is + not required for Pascal.} + + \item{The memory model is always large: functions are far, data + pointers are far, and no data item can be more than 64K long. + (Actually, some functions are near, but only those functions that + are local to a Pascal unit and never called from outside it. All + assembly functions that Pascal calls, and all Pascal functions that + assembly routines are able to call, are far.) However, all static + data declared in a Pascal program goes into the default data + segment, which is the one whose segment address will be in \code{DS} + when control is passed to your assembly code. The only things that + do not live in the default data segment are local variables (they + live in the stack segment) and dynamically allocated variables. All + data \emph{pointers}, however, are far.} + + \item{The function calling convention is different - described below.} + + \item{Some data types, such as strings, are stored differently.} + + \item{There are restrictions on the segment names you are allowed to + use - Borland Pascal will ignore code or data declared in a segment + it doesn't like the name of. The restrictions are described below.} +\end{itemize} + +\xsubsection{16bpfunc}{The Pascal Calling Convention} + +\index{functions!Pascal calling convention}\index{Pascal calling +convention}The 16-bit Pascal calling convention is as follows. In +the following description, the words \emph{caller} and \emph{callee} are +used to denote the function doing the calling and the function which +gets called. + +\begin{itemize} + \item{The caller pushes the function's parameters on the stack, one + after another, in normal order (left to right, so that the first + argument specified to the function is pushed first).} + + \item{The caller then executes a far \code{CALL} instruction to pass + control to the callee.} + + \item{The callee receives control, and typically (although this is not + actually necessary, in functions which do not need to access their + parameters) starts by saving the value of \code{SP} in \code{BP} so as to + be able to use \code{BP} as a base pointer to find its parameters on + the stack. However, the caller was probably doing this too, so part + of the calling convention states that \code{BP} must be preserved by + any function. Hence the callee, if it is going to set up \code{BP} as a + \textindex{frame pointer}, must push the previous value first.} + + \item{The callee may then access its parameters relative to \code{BP}. + The word at \code{[BP]} holds the previous value of \code{BP} as it was + pushed. The next word, at \code{[BP+2]}, holds the offset part of the + return address, and the next one at \code{[BP+4]} the segment part. The + parameters begin at \code{[BP+6]}. The rightmost parameter of the + function, since it was pushed last, is accessible at this offset + from \code{BP}; the others follow, at successively greater offsets.} + + \item{The callee may also wish to decrease \code{SP} further, so as to + allocate space on the stack for local variables, which will then be + accessible at negative offsets from \code{BP}.} + + \item{The callee, if it wishes to return a value to the caller, should + leave the value in \code{AL}, \code{AX} or \code{DX:AX} depending on + the size of the value. Floating-point results are returned in \code{ST0}. + Results of type \code{Real} (Borland's own custom floating-point data + type, not handled directly by the FPU) are returned in \code{DX:BX:AX}. + To return a result of type \code{String}, the caller pushes a pointer + to a temporary string before pushing the parameters, and the callee + places the returned string value at that location. The pointer is + not a parameter, and should not be removed from the stack by the + \code{RETF} instruction.} + + \item{Once the callee has finished processing, it restores \code{SP} from + \code{BP} if it had allocated local stack space, then pops the previous + value of \code{BP}, and returns via \code{RETF}. It uses the form of + \code{RETF} with an immediate parameter, giving the number of bytes + taken up by the parameters on the stack. This causes the parameters + to be removed from the stack as a side effect of the return + instruction.} + + \item{When the caller regains control from the callee, the function + parameters have already been removed from the stack, so it needs to + do nothing further.} +\end{itemize} + +Thus, you would define a function in Pascal style, taking two +\code{Integer}-type parameters, in the following way: + +\begin{lstlisting} +global myfunc + +myfunc: + push bp + mov bp,sp + sub sp,0x40 ; 64 bytes of local stack space + mov bx,[bp+8] ; first parameter to function + mov bx,[bp+6] ; second parameter to function + + ; some more code + + mov sp,bp ; undo "sub sp,0x40" above + pop bp + retf 4 ; total size of params is 4 +\end{lstlisting} + +At the other end of the process, to call a Pascal function from your +assembly code, you would do something like this: + +\begin{lstlisting} +extern SomeFunc + ; and then, further down... + push word seg mystring ; Now push the segment, and... + push word mystring ; ... offset of "mystring" + push word [myint] ; one of my variables + call far SomeFunc +\end{lstlisting} + +This is equivalent to the Pascal code + +\begin{lstlisting} +procedure SomeFunc(String: PChar; Int: Integer); + SomeFunc(@mystring, myint); +\end{lstlisting} + +\xsubsection{16bpseg}{Borland Pascal Segment Name Restrictions} +\index{segment names!Borland Pascal} + +Since Borland Pascal's internal unit file format is completely +different from \code{OBJ}, it only makes a very sketchy job of actually +reading and understanding the various information contained in a +real \code{OBJ} file when it links that in. Therefore an object file +intended to be linked to a Pascal program must obey a number of +restrictions: + +\begin{itemize} + \item{Procedures and functions must be in a segment whose name is + either \code{CODE}, \code{CSEG}, or something ending in + \code{\_TEXT}.} + + \item{initialized data must be in a segment whose name is either + \code{CONST} or something ending in \code{\_DATA}.} + + \item{Uninitialized data must be in a segment whose name is either + \code{DATA}, \code{DSEG}, or something ending in \code{\_BSS}.} + + \item{Any other segments in the object file are completely ignored. + \code{GROUP} directives and segment attributes are also ignored.} +\end{itemize} + +\xsubsection{16bpmacro}{Using \codeindex{c16.mac} With Pascal Programs} + +The \code{c16.mac} macro package, described in \nref{16cmacro}, +can also be used to simplify writing functions to be called from Pascal +programs, if you code \indexcode{PASCAL}\code{\%define PASCAL}. This +definition ensures that functions are far (it implies \codeindex{FARCODE}), +and also causes procedure return instructions to be generated with +an operand. + +Defining \code{PASCAL} does not change the code which calculates the +argument offsets; you must declare your function's arguments in +reverse order. For example: + +\begin{lstlisting} +%define PASCAL + +proc _pascalproc +%$j arg 4 +%$i arg + mov ax,[bp + %$i] + mov bx,[bp + %$j] + mov es,[bp + %$j + 2] + add ax,[bx] +endproc +\end{lstlisting} + +This defines the same routine, conceptually, as the example in +\nref{16cmacro}: it defines a function taking two arguments, +an integer and a pointer to an integer, which returns the sum of +the integer and the contents of the pointer. The only difference +between this code and the large-model C version is that \code{PASCAL} +is defined instead of \code{FARCODE}, and that the arguments are +declared in reverse order. diff --git a/doc/latex/src/32bit.tex b/doc/latex/src/32bit.tex new file mode 100644 index 00000000..47c27466 --- /dev/null +++ b/doc/latex/src/32bit.tex @@ -0,0 +1,539 @@ +% +% vim: ts=4 sw=4 et +% +\xchapter{32bit}{Writing 32-bit Code (Unix, Win32, DJGPP)} + +This chapter attempts to cover some of the common issues involved +when writing 32-bit code, to run under \textindex{Win32} or Unix, +or to be linked with C code generated by a Unix-style C compiler such as +\textindex{DJGPP}. It covers how to write assembly code to interface with +32-bit C routines, and how to write position-independent code for +shared libraries. + +Almost all 32-bit code, and in particular all code running under +\code{Win32}, \code{DJGPP} or any of the PC Unix variants, runs in +\index{flat memory model}\emph{flat} memory model. This means that +the segment registers and paging have already been set up to give +you the same 32-bit 4Gb address space no matter what segment you +work relative to, and that you should ignore all segment registers +completely. When writing flat-model application code, you never +need to use a segment override or modify any segment register, +and the code-section addresses you pass to \code{CALL} and +\code{JMP} live in the same address space as the data-section addresses +you access your variables by and the stack-section addresses you access +local variables and procedure parameters by. Every address is 32 bits +long and contains only an offset part. + +\xsection{32c}{Interfacing to 32-bit C Programs} + +A lot of the discussion in \nref{16c}, about interfacing to +16-bit C programs, still applies when working in 32 bits. The absence of +memory models or segmentation worries simplifies things a lot. + +\xsubsection{32cunder}{External Symbol Names} + +Most 32-bit C compilers share the convention used by 16-bit +compilers, that the names of all global symbols (functions or data) +they define are formed by prefixing an underscore to the name as it +appears in the C program. However, not all of them do: the \code{ELF} +specification states that C symbols do \emph{not} have a leading +underscore on their assembly-language names. + +The older Linux \code{a.out} C compiler, all \code{Win32} compilers, +\code{DJGPP}, and \code{NetBSD} and \code{FreeBSD}, all use the leading +underscore; for these compilers, the macros \code{cextern} and +\code{cglobal}, as given in \nref{16cunder}, will still work. +For \code{ELF}, though, the leading underscore should not be used. + +See also \nref{opt-pfix}. + +\xsubsection{32cfunc}{Function Definitions and Function Calls} + +\index{functions!C calling convention}The \textindex{C calling convention} +in 32-bit programs is as follows. In the following description, +the words \emph{caller} and \emph{callee} are used to denote +the function doing the calling and the function which gets called. + +\begin{itemize} + \item{The caller pushes the function's parameters on the stack, one + after another, in reverse order (right to left, so that the first + argument specified to the function is pushed last).} + + \item{The caller then executes a near \code{CALL} instruction to pass + control to the callee.} + + \item{The callee receives control, and typically (although this + is not actually necessary, in functions which do not need to + access their parameters) starts by saving the value of \code{ESP} + in \code{EBP} so as to be able to use \code{EBP} as a base pointer + to find its parameters on the stack. However, the caller was + probably doing this too, so part of the calling convention states + that \code{EBP} must be preserved by any C function. Hence the + callee, if it is going to set up \code{EBP} as a \textindex{frame + pointer}, must push the previous value first.} + + \item{The callee may then access its parameters relative to \code{EBP}. + The doubleword at \code{[EBP]} holds the previous value of + \code{EBP} as it was pushed; the next doubleword, at \code{[EBP+4]}, + holds the return address, pushed implicitly by \code{CALL}. + The parameters start after that, at \code{[EBP+8]}. The leftmost + parameter of the function, since it was pushed last, is accessible + at this offset from \code{EBP}; the others follow, at successively + greater offsets. Thus, in a function such as \code{printf} which + takes a variable number of parameters, the pushing of the + parameters in reverse order means that the function knows where + to find its first parameter, which tells it the number and type + of the remaining ones.} + + \item{The callee may also wish to decrease \code{ESP} further, so as + to allocate space on the stack for local variables, which will + then be accessible at negative offsets from \code{EBP}.} + + \item{The callee, if it wishes to return a value to the caller, + should leave the value in \code{AL}, \code{AX} or \code{EAX} + depending on the size of the value. Floating-point results + are typically returned in \code{ST0}.} + + \item{Once the callee has finished processing, it restores + \code{ESP} from \code{EBP} if it had allocated local stack space, + then pops the previous value of \code{EBP}, and returns via + \code{RET} (equivalently, \code{RETN}).} + + \item{When the caller regains control from the callee, the function + parameters are still on the stack, so it typically adds an + immediate constant to \code{ESP} to remove them (instead of + executing a number of slow \code{POP} instructions). Thus, + if a function is accidentally called with the wrong number + of parameters due to a prototype mismatch, the stack will + still be returned to a sensible state since the caller, which + \emph{knows} how many parameters it pushed, does the + removing.} +\end{itemize} + +There is an alternative calling convention used by Win32 programs +for Windows API calls, and also for functions called \emph{by} the +Windows API such as window procedures: they follow what Microsoft +calls the \code{\_\_stdcall} convention. This is slightly closer to the +Pascal convention, in that the callee clears the stack by passing a +parameter to the \code{RET} instruction. However, the parameters are +still pushed in right-to-left order. + +Thus, you would define a function in C style in the following way: + +\begin{lstlisting} +global _myfunc + +_myfunc: + push ebp + mov ebp,esp + sub esp,0x40 ; 64 bytes of local stack space + mov ebx,[ebp+8] ; first parameter to function + + ; some more code + + leave ; mov esp,ebp / pop ebp + ret +\end{lstlisting} + +At the other end of the process, to call a C function from your +assembly code, you would do something like this: + +\begin{lstlisting} +extern _printf + + ; and then, further down... + + push dword [myint] ; one of my integer variables + push dword mystring ; pointer into my data segment + call _printf + add esp,byte 8 ; `byte' saves space + + ; then those data items... + +segment _DATA + +myint dd 1234 +mystring db 'This number -> %d <- should be 1234',10,0 +\end{lstlisting} + +This piece of code is the assembly equivalent of the C code + +\begin{lstlisting} + int myint = 1234; + printf("This number -> %d <- should be 1234\n", myint); +\end{lstlisting} + +\xsubsection{32cdata}{Accessing Data Items} + +To get at the contents of C variables, or to declare variables which +C can access, you need only declare the names as \code{GLOBAL} or +\code{EXTERN}. (Again, the names require leading underscores, as stated +in \nref{32cunder}.) Thus, a C variable declared as \code{int i} +can be accessed from assembler as + +\begin{lstlisting} + extern _i + mov eax,[_i] +\end{lstlisting} + +And to declare your own integer variable which C programs can access +as \code{extern int j}, you do this (making sure you are assembling in +the \code{\_DATA} segment, if necessary): + +\begin{lstlisting} + global _j +_j dd 0 +\end{lstlisting} + +To access a C array, you need to know the size of the components of +the array. For example, \code{int} variables are four bytes long, so if +a C program declares an array as \code{int a[10]}, you can access +\code{a[3]} by coding \code{mov ax,[\_a+12]}. (The byte offset 12 is +obtained by multiplying the desired array index, 3, by the size of +the array element, 4.) The sizes of the C base types in 32-bit compilers +are: 1 for \code{char}, 2 for \code{short}, 4 for \code{int}, \code{long} +and \code{float}, and 8 for \code{double}. Pointers, being 32-bit +addresses, are also 4 bytes long. + +To access a C \textindex{data structure}, you need to know the offset from +the base of the structure to the field you are interested in. You +can either do this by converting the C structure definition into a +NASM structure definition (using \code{STRUC}), or by calculating the +one offset and using just that. + +To do either of these, you should read your C compiler's manual to +find out how it organizes data structures. NASM gives no special +alignment to structure members in its own \codeindex{STRUC} macro, +so you have to specify alignment yourself if the C compiler generates it. +Typically, you might find that a structure like + +\begin{lstlisting} +struct { + char c; + int i; +} foo; +\end{lstlisting} + +might be eight bytes long rather than five, since the \code{int} field +would be aligned to a four-byte boundary. However, this sort of +feature is sometimes a configurable option in the C compiler, either +using command-line options or \code{\#pragma} lines, so you have to find +out how your own compiler does it. + +\xsubsection{32cmacro}{\codeindex{c32.mac}: Helper Macros for the 32-bit C Interface} + +Included in the NASM archives, in the \index{misc directory}\code{misc} +directory, is a file \code{c32.mac} of macros. It defines three macros: +\codeindex{proc}, \codeindex{arg} and \codeindex{endproc}. These are +intended to be used for C-style procedure definitions, and they automate +a lot of the work involved in keeping track of the calling convention. + +An example of an assembly function using the macro set is given +here: + +\begin{lstlisting} +proc _proc32 +%$i arg +%$j arg + mov eax,[ebp + %$i] + mov ebx,[ebp + %$j] + add eax,[ebx] +endproc +\end{lstlisting} + +This defines \code{\_proc32} to be a procedure taking two arguments, the +first (\code{i}) an integer and the second (\code{j}) a pointer to an +integer. It returns \code{i + *j}. + +Note that the \code{arg} macro has an \code{EQU} as the first line of its +expansion, and since the label before the macro call gets prepended +to the first line of the expanded macro, the \code{EQU} works, defining +\code{\%\$i} to be an offset from \code{BP}. A context-local variable is +used, local to the context pushed by the \code{proc} macro and popped +by the \code{endproc} macro, so that the same argument name can be used +in later procedures. Of course, you don't \emph{have} to do that. + +\code{arg} can take an optional parameter, giving the size of the +argument. If no size is given, 4 is assumed, since it is likely that +many function parameters will be of type \code{int} or pointers. + +\xsection{picdll}{Writing NetBSD/FreeBSD/OpenBSD and Linux/ELF} +\index{Shared Libraries} + +\code{ELF} replaced the older \code{a.out} object file format under Linux +because it contains support for \textindex{position-independent code} +(\textindex{PIC}), which makes writing shared libraries much easier. NASM +supports the \code{ELF} position-independent code features, so you can +write Linux \code{ELF} shared libraries in NASM. + +\textindex{NetBSD}, and its close cousins \textindex{FreeBSD} and +\textindex{OpenBSD}, take a different approach by hacking PIC support +into the \code{a.out} format. NASM supports this as the \codeindex{aoutb} +output format, so you can write \textindex{BSD} shared libraries in +NASM too. + +The operating system loads a PIC shared library by memory-mapping +the library file at an arbitrarily chosen point in the address space +of the running process. The contents of the library's code section +must therefore not depend on where it is loaded in memory. + +Therefore, you cannot get at your variables by writing code like +this: + +\begin{lstlisting} + mov eax,[myvar] ; WRONG +\end{lstlisting} + +Instead, the linker provides an area of memory called the +\textindex{global offset table}, or \textindex{GOT}; the GOT is situated +at a constant distance from your library's code, so if you can find out +where your library is loaded (which is typically done using a \code{CALL} +and \code{POP} combination), you can obtain the address of the GOT, and +you can then load the addresses of your variables out of linker-generated +entries in the GOT. + +The \emph{data} section of a PIC shared library does not have these +restrictions: since the data section is writable, it has to be +copied into memory anyway rather than just paged in from the library +file, so as long as it's being copied it can be relocated too. So +you can put ordinary types of relocation in the data section without +too much worry (but see \nref{picglobal} for a caveat). + +\xsubsection{picgot}{Obtaining the Address of the GOT} + +Each code module in your shared library should define the GOT as an +external symbol: + +\begin{lstlisting} +extern _GLOBAL_OFFSET_TABLE_ ; in ELF +extern __GLOBAL_OFFSET_TABLE_ ; in BSD a.out +\end{lstlisting} + +At the beginning of any function in your shared library which plans +to access your data or BSS sections, you must first calculate the +address of the GOT. This is typically done by writing the function +in this form: + +\begin{lstlisting} +func: + push ebp + mov ebp,esp + push ebx + call .get_GOT +.get_GOT: + pop ebx + add ebx,_GLOBAL_OFFSET_TABLE_+$$-.get_GOT wrt ..gotpc + + ; the function body comes here + + mov ebx,[ebp-4] + mov esp,ebp + pop ebp + ret +\end{lstlisting} + +(For BSD, again, the symbol \code{\_GLOBAL\_OFFSET\_TABLE} requires a +second leading underscore.) + +The first two lines of this function are simply the standard C +prologue to set up a stack frame, and the last three lines are +standard C function epilogue. The third line, and the fourth to last +line, save and restore the \code{EBX} register, because PIC shared +libraries use this register to store the address of the GOT. + +The interesting bit is the \code{CALL} instruction and the following +two lines. The \code{CALL} and \code{POP} combination obtains the address +of the label \code{.get\_GOT}, without having to know in advance where +the program was loaded (since the \code{CALL} instruction is encoded +relative to the current position). The \code{ADD} instruction makes use +of one of the special PIC relocation types: \textindex{GOTPC relocation}. +With the \codeindex{WRT ..gotpc} qualifier specified, the symbol +referenced (here \code{\_GLOBAL\_OFFSET\_TABLE\_}, the special symbol +assigned to the GOT) is given as an offset from the beginning of the +section. (Actually, \code{ELF} encodes it as the offset from the operand +field of the \code{ADD} instruction, but NASM simplifies this +deliberately, so you do things the same way for both \code{ELF} and +\code{BSD}.) So the instruction then \emph{adds} the beginning of the +section, to get the real address of the GOT, and subtracts the value of +\code{.get\_GOT} which it knows is in \code{EBX}. Therefore, by the time +that instruction has finished, \code{EBX} contains the address of the GOT. + +If you didn't follow that, don't worry: it's never necessary to +obtain the address of the GOT by any other means, so you can put +those three instructions into a macro and safely ignore them: + +\begin{lstlisting} +%macro get_GOT 0 + call %%getgot +%%getgot: + pop ebx + add ebx,_GLOBAL_OFFSET_TABLE_+$$-%%getgot wrt ..gotpc +%endmacro +\end{lstlisting} + +\xsubsection{piclocal}{Finding Your Local Data Items} + +Having got the GOT, you can then use it to obtain the addresses of +your data items. Most variables will reside in the sections you have +declared; they can be accessed using the \index{GOTOFF relocation} +\code{..gotoff} special \indexcode{WRT ..gotoff}\code{WRT} type. The +way this works is like this: + +\begin{lstlisting} + lea eax,[ebx+myvar wrt ..gotoff] +\end{lstlisting} + +The expression \code{myvar wrt ..gotoff} is calculated, when the shared +library is linked, to be the offset to the local variable \code{myvar} +from the beginning of the GOT. Therefore, adding it to \code{EBX} as +above will place the real address of \code{myvar} in \code{EAX}. + +If you declare variables as \code{GLOBAL} without specifying a size for +them, they are shared between code modules in the library, but do +not get exported from the library to the program that loaded it. +They will still be in your ordinary data and BSS sections, so you +can access them in the same way as local variables, using the above +\code{..gotoff} mechanism. + +Note that due to a peculiarity of the way BSD \code{a.out} format +handles this relocation type, there must be at least one non-local +symbol in the same section as the address you're trying to access. + +\xsubsection{picextern}{Finding External and Common Data Items} + +If your library needs to get at an external variable (external to +the \emph{library}, not just to one of the modules within it), you must +use the \index{GOT relocations}\indexcode{WRT ..got}\code{..got} type +to get at it. The \code{..got} type, instead of giving you the offset from +the GOT base to the variable, gives you the offset from the GOT base to +a GOT \emph{entry} containing the address of the variable. The linker +will set up this GOT entry when it builds the library, and the +dynamic linker will place the correct address in it at load time. So +to obtain the address of an external variable \code{extvar} in \code{EAX}, +you would code + +\begin{lstlisting} + mov eax,[ebx+extvar wrt ..got] +\end{lstlisting} + +This loads the address of \code{extvar} out of an entry in the GOT. The +linker, when it builds the shared library, collects together every +relocation of type \code{..got}, and builds the GOT so as to ensure it +has every necessary entry present. + +Common variables must also be accessed in this way. + +\xsubsection{picglobal}{Exporting Symbols to the Library User} + +If you want to export symbols to the user of the library, you have +to declare whether they are functions or data, and if they are data, +you have to give the size of the data item. This is because the +dynamic linker has to build \index{PLT}\textindex{procedure linkage table} +entries for any exported functions, and also moves exported data +items away from the library's data section in which they were +declared. + +So to export a function to users of the library, you must use + +\begin{lstlisting} +global func:function ; declare it as a function +func: + push ebp + ; etc. +\end{lstlisting} + +And to export a data item such as an array, you would have to code + +\begin{lstlisting} +global array:data array.end-array ; give the size too + array: resd 128 +.end: +\end{lstlisting} + +Be careful: If you export a variable to the library user, by +declaring it as \code{GLOBAL} and supplying a size, the variable will +end up living in the data section of the main program, rather than +in your library's data section, where you declared it. So you will +have to access your own global variable with the \code{..got} mechanism +rather than \code{..gotoff}, as if it were external (which, +effectively, it has become). + +Equally, if you need to store the address of an exported global in +one of your data sections, you can't do it by means of the standard +sort of code: + +\begin{lstlisting} +dataptr: dd global_data_item ; WRONG +\end{lstlisting} + +NASM will interpret this code as an ordinary relocation, in which +\code{global\_data\_item} is merely an offset from the beginning of the +\code{.data} section (or whatever); so this reference will end up +pointing at your data section instead of at the exported global +which resides elsewhere. + +Instead of the above code, then, you must write + +\begin{lstlisting} +dataptr: dd global_data_item wrt ..sym +\end{lstlisting} + +which makes use of the special \code{WRT} type \indexcode{WRT ..sym} +\code{..sym} to instruct NASM to search the symbol table for a particular +symbol at that address, rather than just relocating by section base. + +Either method will work for functions: referring to one of your +functions by means of + +\begin{lstlisting} +funcptr: dd my_function +\end{lstlisting} + +will give the user the address of the code you wrote, whereas + +\begin{lstlisting} +funcptr: dd my_function wrt ..sym +\end{lstlisting} + +will give the address of the procedure linkage table for the +function, which is where the calling program will \emph{believe} the +function lives. Either address is a valid way to call the function. + +\xsubsection{picproc}{Calling Procedures Outside the Library} + +Calling procedures outside your shared library has to be done by +means of a \textindex{procedure linkage table}, or \textindex{PLT}. +The PLT is placed at a known offset from where the library is loaded, +so the library code can make calls to the PLT in a position-independent +way. Within the PLT there is code to jump to offsets contained in +the GOT, so function calls to other shared libraries or to routines +in the main program can be transparently passed off to their real +destinations. + +To call an external routine, you must use another special PIC +relocation type, \index{PLT relocations}\codeindex{WRT ..plt}. This is +much easier than the GOT-based ones: you simply replace calls such as +\code{CALL printf} with the PLT-relative version \code{CALL printf WRT +..plt}. + +\xsubsection{link}{Generating the Library File} + +Having written some code modules and assembled them to \code{.o} files, +you then generate your shared library with a command such as + +\begin{lstlisting} +ld -shared -o library.so module1.o module2.o # for ELF +ld -Bshareable -o library.so module1.o module2.o # for BSD +\end{lstlisting} + +For ELF, if your shared library is going to reside in system +directories such as \code{/usr/lib} or \code{/lib}, it is usually worth +using the \codeindex{-soname} flag to the linker, to store the final +library file name, with a version number, into the library: + +\begin{lstlisting} +ld -shared -soname library.so.1 -o library.so.1.2 *.o +\end{lstlisting} + +You would then copy \code{library.so.1.2} into the library directory, +and create \code{library.so.1} as a symbolic link to it. diff --git a/doc/latex/src/64bit.tex b/doc/latex/src/64bit.tex new file mode 100644 index 00000000..5aaf20f6 --- /dev/null +++ b/doc/latex/src/64bit.tex @@ -0,0 +1,204 @@ +% +% vim: ts=4 sw=4 et +% +\xchapter{64bit}{Writing 64-bit Code (Unix, Win64)} + +This chapter attempts to cover some of the common issues involved when +writing 64-bit code, to run under \textindex{Win64} or Unix. It covers +how to write assembly code to interface with 64-bit C routines, and +how to write position-independent code for shared libraries. + +All 64-bit code uses a flat memory model, since segmentation is not +available in 64-bit mode. The one exception is the \code{FS} and +\code{GS} registers, which still add their bases. + +Position independence in 64-bit mode is significantly simpler, since +the processor supports \code{RIP}-relative addressing directly; see the +\code{REL} keyword (\nref{effaddr}). On most 64-bit platforms, +it is probably desirable to make that the default, using the directive +\code{DEFAULT REL} (\nref{default}). + +64-bit programming is relatively similar to 32-bit programming, but +of course pointers are 64 bits long; additionally, all existing +platforms pass arguments in registers rather than on the stack. +Furthermore, 64-bit platforms use SSE2 by default for floating point. +Please see the ABI documentation for your platform. + +64-bit platforms differ in the sizes of the C/C++ fundamental +datatypes, not just from 32-bit platforms but from each other. If a +specific size data type is desired, it is probably best to use the +types defined in the standard C header \code{<inttypes.h>}. + +All known 64-bit platforms except some embedded platforms require that +the stack is 16-byte aligned at the entry to a function. In order to +enforce that, the stack pointer (\code{RSP}) needs to be aligned on an +\code{odd} multiple of 8 bytes before the \code{CALL} instruction. + +In 64-bit mode, the default instruction size is still 32 bits. When +loading a value into a 32-bit register (but not an 8- or 16-bit +register), the upper 32 bits of the corresponding 64-bit register are +set to zero. + +\xsection{reg64}{Register Names in 64-bit Mode} + +NASM uses the following names for general-purpose registers in 64-bit +mode, for 8-, 16-, 32- and 64-bit references, respectively: + +\begin{lstlisting} +AL/AH, CL/CH, DL/DH, BL/BH, SPL, BPL, SIL, DIL, R8B-R15B +AX, CX, DX, BX, SP, BP, SI, DI, R8W-R15W +EAX, ECX, EDX, EBX, ESP, EBP, ESI, EDI, R8D-R15D +RAX, RCX, RDX, RBX, RSP, RBP, RSI, RDI, R8-R15 +\end{lstlisting} + +This is consistent with the AMD documentation and most other +assemblers. The Intel documentation, however, uses the names +\code{R8L-R15L} for 8-bit references to the higher registers. It is +possible to use those names by definiting them as macros; similarly, +if one wants to use numeric names for the low 8 registers, define them +as macros. The standard macro package \code{altreg} (see +\nref{pkgaltreg}) can be used for this purpose. + +\xsection{id64}{Immediates and Displacements in 64-bit Mode} + +In 64-bit mode, immediates and displacements are generally only 32 +bits wide. NASM will therefore truncate most displacements and +immediates to 32 bits. + +The only instruction which takes a full \textindex{64-bit immediate} is: + +\begin{lstlisting} +mov reg64,imm64 +\end{lstlisting} + +NASM will produce this instruction whenever the programmer uses +\code{MOV} with an immediate into a 64-bit register. If this is not +desirable, simply specify the equivalent 32-bit register, which will +be automatically zero-extended by the processor, or specify the +immediate as \code{DWORD}: + +\begin{lstlisting} +mov rax,foo ; 64-bit immediate +mov rax,qword foo ; (identical) +mov eax,foo ; 32-bit immediate, zero-extended +mov rax,dword foo ; 32-bit immediate, sign-extended +\end{lstlisting} + +The length of these instructions are 10, 5 and 7 bytes, respectively. + +If optimization is enabled and NASM can determine at assembly time +that a shorter instruction will suffice, the shorter instruction will +be emitted unless of course \code{STRICT QWORD} or \code{STRICT DWORD} +is specified (see \nref{strict}): + +\begin{lstlisting} +mov rax,1 ; Assembles as "mov eax,1" (5 bytes) +mov rax,strict qword 1 ; Full 10-byte instruction +mov rax,strict dword 1 ; 7-byte instruction +mov rax,symbol ; 10 bytes, not known at assembly time +lea rax,[rel symbol] ; 7 bytes, usually preferred by the ABI +\end{lstlisting} + +Note that \code{lea rax,[rel symbol]} is position-independent, whereas +\code{mov rax,symbol} is not. Most ABIs prefer or even require +position-independent code in 64-bit mode. However, the \code{MOV} +instruction is able to reference a symbol anywhere in the 64-bit +address space, whereas \code{LEA} is only able to access a symbol within +within 2 GB of the instruction itself (see below.) + +The only instructions which take a full \textindex{64-bit displacement} +is loading or storing, using \code{MOV}, \code{AL}, \code{AX}, \code{EAX} +or \code{RAX} (but no other registers) to an absolute 64-bit address. +Since this is a relatively rarely used instruction (64-bit code +generally uses relative addressing), the programmer has to explicitly +declare the displacement size as \code{ABS QWORD}: + +\begin{lstlisting} +default abs + +mov eax,[foo] ; 32-bit absolute disp, sign-extended +mov eax,[a32 foo] ; 32-bit absolute disp, zero-extended +mov eax,[qword foo] ; 64-bit absolute disp + +default rel + +mov eax,[foo] ; 32-bit relative disp +mov eax,[a32 foo] ; d:o, address truncated to 32 bits(!) +mov eax,[qword foo] ; error +mov eax,[abs qword foo] ; 64-bit absolute disp +\end{lstlisting} + +A sign-extended absolute displacement can access from -2 GB to +2 GB; +a zero-extended absolute displacement can access from 0 to 4 GB. + +\xsection{unix64}{Interfacing to 64-bit C Programs (Unix)} + +On Unix, the 64-bit ABI as well as the x32 ABI (32-bit ABI with the +CPU in 64-bit mode) is defined by the documents at +\href{http://www.nasm.us/abi/unix64}{http://www.nasm.us/abi/unix64} + +Although written for AT\&T-syntax assembly, the concepts apply equally +well for NASM-style assembly. What follows is a simplified summary. + +The first six integer arguments (from the left) are passed in \code{RDI}, +\code{RSI}, \code{RDX}, \code{RCX}, \code{R8}, and \code{R9}, in that +order. Additional integer arguments are passed on the stack. These +registers, plus \code{RAX}, \code{R10} and \code{R11} are destroyed +by function calls, and thus are available for use by the function +without saving. + +Integer return values are passed in \code{RAX} and \code{RDX}, +in that order. + +Floating point is done using SSE registers, except for \code{long double}, +which is 80 bits (\code{TWORD}) on most platforms (Android is +one exception; there \code{long double} is 64 bits and treated the same +as \code{double}.) Floating-point arguments are passed in \code{XMM0} to +\code{XMM7}; return is \code{XMM0} and \code{XMM1}. \code{long double} +are passed on the stack, and returned in \code{ST0} and \code{ST1}. + +All SSE and x87 registers are destroyed by function calls. + +On 64-bit Unix, \code{long} is 64 bits. + +Integer and SSE register arguments are counted separately, so +for the case of + +\begin{lstlisting} +void foo(long a, double b, int c) +\end{lstlisting} + +\code{a} is passed in \code{RDI}, \code{b} in \code{XMM0}, +and \code{c} in \code{ESI}. + +\xsection{win64}{Interfacing to 64-bit C Programs (Win64)} + +The Win64 ABI is described by the document at +\href{http://www.nasm.us/abi/win64}{http://www.nasm.us/abi/win64} + +What follows is a simplified summary. + +The first four integer arguments are passed in \code{RCX}, \code{RDX}, +\code{R8} and \code{R9}, in that order. Additional integer arguments are +passed on the stack. These registers, plus \code{RAX}, \code{R10} and +\code{R11} are destroyed by function calls, and thus are available for +use by the function without saving. + +Integer return values are passed in \code{RAX} only. + +Floating point is done using SSE registers, except for \code{long +double}. Floating-point arguments are passed in \code{XMM0} +to \code{XMM3}; return is \code{XMM0} only. + +On Win64, \code{long} is 32 bits; \code{long long} or \code{\_int64} +is 64 bits. + +Integer and SSE register arguments are counted together, so +for the case of + +\begin{lstlisting} +void foo(long long a, double b, int c) +\end{lstlisting} + +\code{a} is passed in \code{RCX}, \code{b} in \code{XMM1}, +and \code{c} in \code{R8D}. diff --git a/doc/latex/src/changelog.tex b/doc/latex/src/changelog.tex new file mode 100644 index 00000000..4a03a6be --- /dev/null +++ b/doc/latex/src/changelog.tex @@ -0,0 +1,2304 @@ +% +% vim: ts=4 sw=4 et +% +\xchapter{changelog}{\textindexlc{NASM Version History}} + +\xsection{cl-2.xx}{NASM 2 Series} + +The NASM 2 series supports x86-64, and is the production version of NASM +since 2007. + +\xsubsection{cl-2.15}{Version 2.15} + +\begin{itemize} + \item{The state of warnings can now be saved and restored via + the \code{[WARNING PUSH]} and \code{[WARNING POP]} directives. + See \nref{asmdir-warning}}. +\end{itemize} + +\xsubsection{cl-2.14.03}{Version 2.14.03} + +\begin{itemize} + \item{Suppress nuisance "\code{label changed during code + generation}" messages after a real error.} +\end{itemize} + +\xsubsection{cl-2.14.02}{Version 2.14.02} + +\begin{itemize} + \item{Fix crash due to multiple errors or warnings during the code + generation pass if a list file is specified.} +\end{itemize} + +\xsubsection{cl-2.14.01}{Version 2.14.01} + +\begin{itemize} + \item{Create all system-defined macros defore processing command-line + given preprocessing directives (\code{-p}, \code{-d}, \code{-u}, \code{--pragma}, + \code{--before}).} + + \item{If debugging is enabled, define a \code{\_\_DEBUG\_FORMAT\_\_} predefined + macro. See \nref{dfmtm}.} + + \item{Fix an assert for the case in the \code{obj} format when a \code{SEG} + operator refers to an \code{EXTERN} symbol declared further down in the + code.} + + \item{Fix a corner case in the floating-point code where a binary, octal + or hexadecimal floating-point having at least 32, 11, or 8 mantissa + digits could produce slightly incorrect results under very specific + conditions.} + + \item{Support \code{-MD} without a filename, for \code{gcc} compatibility. + \code{-MF} can be used to set the dependencies output filename. + See \nref{opt-MD}.} + + \item{Fix \code{-E} in combination with \code{-MD}. See \nref{opt-E}.} + + \item{Fix missing errors on redefined labels; would cause convergence + failure instead which is very slow and not easy to debug.} + + \item{Duplicate definitions of the same label \emph{with the same value} is now + explicitly permitted (2.14 would allow it in some circumstances.)} + + \item{Add the option \code{--no-line} to ignore \code{\%line} directives in the + source. See \nref{opt-no-line} and \nref{line}.} +\end{itemize} + +\xsubsection{cl-2.14}{Version 2.14} + +\begin{itemize} + \item{Changed \code{-I} option semantics by adding a trailing path + separator unconditionally.} + + \item{Fixed null dereference in corrupted invalid single line macros.} + + \item{Fixed division by zero which may happen if source code is malformed.} + + \item{Fixed out of bound access in processing of malformed segment override.} + + \item{Fixed out of bound access in certain \code{EQU} parsing.} + + \item{Fixed buffer underflow in float parsing.} + + \item{Added \code{SGX} (Intel Software Guard Extensions) instructions.} + + \item{Added \code{+n} syntax for multiple contiguous registers.} + + \item{Fixed \code{subsections\_via\_symbols} for \code{macho} object format.} + + \item{Added the \code{--gprefix}, \code{--gpostfix}, \code{--lprefix}, and + \code{--lpostfix} command line options, to allow command line base symbol + renaming. See \nref{opt-pfix}.} + + \item{Allow label renaming to be specified by \code{\%pragma} in addition to + from the command line. See \nref{mangling}.} + + \item{Supported generic \code{\%pragma} namespaces, \code{output} and \code{debug}. + See \nref{gen-namespace}.} + + \item{Added the \code{--pragma} command line option to inject a \code{\%pragma} + directive. See \nref{opt-pragma}.} + + \item{Added the \code{--before} command line option to accept preprocess + statement before input. See \nref{opt-before}.} + + \item{Added \code{AVX512} \code{VBMI2} (Additional Bit Manipulation), \code{VNNI} + (Vector Neural Network), \code{BITALG} (Bit Algorithm), and \code{GFNI} (Galois + Field New Instruction) instructions.} + + \item{Added the \code{STATIC} directive for local symbols that should be + renamed using global-symbol rules. See \nref{static}.} + + \item{Allow a symbol to be defined as \code{EXTERN} and then later + overridden as \code{GLOBAL} or \code{COMMON}. Furthermore, a symbol + declared \code{EXTERN} and then defined will be treated as \code{GLOBAL}. + See \nref{extern}.} + + \item{The \code{GLOBAL} directive no longer is required to precede the + definition of the symbol.} + + \item{Support \code{private\_extern} as \code{macho} specific extension to the + \code{GLOBAL} directive. See \nref{macho-pext}.} + + \item{Updated \code{UD0} encoding to match with the specification} + + \item{Added the \code{--limit-X} command line option to set execution + limits. See \nref{opt-limit}.} + + \item{Updated the \code{Codeview} version number to be aligned with \code{MASM}.} + + \item{Added the \code{--keep-all} command line option to preserve output + files. See \nref{opt-keep-all}.} + + \item{Added the \code{--include} command line option, an alias to \code{-P} + (\nref{opt-p}).} + + \item{Added the \code{--help} command line option as an alias to \code{-h} + (\nref{syntax}).} + + \item{Added \code{-W}, \code{-D}, and \code{-Q} suffix aliases for \code{RET} + instructions so the operand sizes of these instructions can be + encoded without using \code{o16}, \code{o32} or \code{o64}.} +\end{itemize} + +\xsubsection{cl-2.13.03}{Version 2.13.03} + +\begin{itemize} + \item{Added AVX and AVX512 \code{VAES*} and \code{VPCLMULQDQ} instructions.} + \item{Fixed missing dwarf record in x32 ELF output format.} +\end{itemize} + +\xsubsection{cl-2.13.02}{Version 2.13.02} + +\begin{itemize} + \item{Fix false positive in testing of numeric overflows.} + + \item{Fix generation of \code{PEXTRW} instruction.} + + \item{Fix \code{smartalign} package which could trigger an error during + optimization if the alignment code expanded too much due to + optimization of the previous code.} + + \item{Fix a case where negative value in \code{TIMES} directive causes + panic instead of an error.} + + \item{Always finalize \code{.debug\_abbrev} section with a null in + \code{dwarf} output format.} + + \item{Support \code{debug} flag in section attributes for \code{macho} + output format. See \nref{machosect}.} + + \item{Support up to 16 characters in section names for \code{macho} + output format.} + + \item{Fix missing update of global \code{BITS} setting if \code{SECTION} + directive specified a bit size using output format-specific + extensions (e.g. \code{USE32} for the \code{obj} output format.)} + + \item{Fix the incorrect generation of VEX-encoded instruction when static + mode decorators are specified on scalar instructions, losing the + decorators as they require EVEX encoding.} + + \item{Option \code{-MW} to quote dependency outputs according to Watcom + Make conventions instead of POSIX Make conventions. See \nref{opt-MW}.} + + \item{The \code{obj} output format now contains embedded dependency file + information, unless disabled with \code{\%pragma obj nodepend}. See + \nref{objdepend}.} + + \item{Fix generation of dependency lists.} + + \item{Fix a number of null pointer reference and memory allocation errors.} + + \item{Always generate symbol-relative relocations for the \code{macho64} + output format; at least some versions of the XCode/LLVM linker fails + for section-relative relocations.} +\end{itemize} + +\xsubsection{cl-2.13.01}{Version 2.13.01} + +\begin{itemize} + \item{Fix incorrect output for some types of \code{FAR} or \code{SEG} + references in the \code{obj} output format, and possibly other 16-bit + output formats.} + + \item{Fix the address in the list file for an instruction containing a + \code{TIMES} directive.} + + \item{Fix error with \code{TIMES} used together with an instruction which + can vary in size, e.g. \code{JMP}.} + + \item{Fix breakage on some uses of the \code{DZ} pseudo-op.} +\end{itemize} + +\xsubsection{cl-2.13}{Version 2.13} + +\begin{itemize} + \item{Support the official forms of the \code{UD0} and \code{UD1} instructions.} + + \item{Allow self-segment-relative expressions in immediates and + displacements, even when combined with an external or otherwise + out-of-segment special symbol, e.g.: +\begin{lstlisting} +extern foo +mov eax,[foo - $ + ebx] ; Now legal +\end{lstlisting}} + + \item{Handle a 64-bit origin in NDISASM.} + + \item{NASM can now generate sparse output files for relevant output + formats, if the underlying operating system supports them.} + + \item{The \code{macho} object format now supports the + \code{subsections\_via\_symbols} and \code{no\_dead\_strip} + directives, see \nref{macho-ssvs}.} + + \item{The \code{macho} object format now supports the \code{no\_dead\_strip}, + \code{live\_support} and \code{strip\_static\_syms} section flags, + see \nref{machosect}.} + + \item{The \code{macho} object format now supports the \code{dwarf} debugging + format, as required by newer toolchains.} + + \item{All warnings can now be suppressed if desired; warnings not + otherwise part of any warning class are now considered its own + warning class called \code{other} (e.g. \code{-w-other}). Furthermore, + warning-as-error can now be controlled on a per warning class + basis, using the syntax \code{-w+error=}\emph{warning-class} and its + equivalent for all other warning control options. See \nref{opt-w} + for the command-line options and warning classes and + \nref{asmdir-warning} for the \code{[WARNING]} directive.} + + \item{Fix a number of bugs related to AVX-512 decorators.} + + \item{Significant improvements to building NASM with Microsoft Visual + Studio via \code{Mkfiles/msvc.mak}. It is now possible to build the + full Windows installer binary as long as the necessary + prerequisites are installed; see \code{Mkfiles/README}} + + \item{To build NASM with custom modifications (table changes) or from the + git tree now requires Perl 5.8 at the very minimum, quite possibly + a higher version (Perl 5.24.1 tested.) There is no requirement to + have Perl on your system at all if all you want to do is build + unmodified NASM from source archives.} + + \item{Fix the \code{\{z\}} decorator on AVX-512 \code{VMOVDQ*} + instructions.} + + \item{Add new warnings for certain dangerous constructs which never ought + to have been allowed. In particular, the \code{RESB} family of + instructions should have been taking a critical expression all + along.} + + \item{Fix the EVEX (AVX-512) versions of the \code{VPBROADCAST}, \code{VPEXTR}, + and \code{VPINSR} instructions.} + + \item{Support contracted forms of additional instructions. As a general + rule, if an instruction has a non-destructive source immediately + after a destination register that isn't used as an input, NASM + supports omitting that source register, using the destination + register as that value. This among other things makes it easier to + convert SSE code to the equivalent AVX code: +\begin{lstlisting} +addps xmm1,xmm0 ; SSE instruction +vaddps ymm1,ymm1,ymm0 ; AVX official long form +vaddps ymm1,ymm0 ; AVX contracted form +\end{lstlisting}} + + \item{Fix Codeview malformed compiler version record.} + + \item{Add the \code{CLWB} and \code{PCOMMIT} instructions. Note that the + \code{PCOMMIT} instruction has been deprecated and will never be + included in a shipping product; it is included for completeness + only.} + + \item{Add the \code{\%pragma} preprocessor directive for + soft-error directives.} + + \item{Add the \code{RDPID} instruction.} +\end{itemize} + +\xsubsection{cl-2.12.02}{Version 2.12.02} + +\begin{itemize} + \item{Fix preprocessor errors, especially \code{\%error} and + \code{\%warning}, inside \code{\%if} statements.} + + \item{Fix relative relocations in 32-bit Mach-O.} + + \item{More Codeview debug format fixes.} + + \item{If the MASM \code{PTR} keyword is encountered, issue a warning. This is + much more likely to indicate a MASM-ism encountered in NASM than it + is a valid label. This warning can be suppressed with \code{-w-ptr}, + the \code{[warning]} directive (see \nref{opt-w}) or by the macro + definition \code{\%idefine ptr \$\%} (see \nref{selfref}).} + + \item{When an error or a warning comes from the expansion of a multi-line + macro, display the file and line numbers for the expanded macros. + Macros defined with \code{.nolist} do not get displayed.} + + \item{Add macros \code{ilog2fw()} and \code{ilog2cw()} to the \code{ifunc} macro + package. See \nref{ilog2}.} +\end{itemize} + +\xsubsection{cl-2.12.01}{Version 2.12.01} + +\begin{itemize} + \item{Portability fixes for some platforms.} + \item{Fix error when not specifying a list file.} + \item{Correct the handling of macro-local labels in the Codeview debugging format.} + \item{Add \code{CLZERO}, \code{MONITORX} and \code{MWAITX} instructions.} +\end{itemize} + +\xsubsection{cl-2.12}{Version 2.12} + +\begin{itemize} + \item{Major fixes to the \code{macho} backend (\nref{machofmt}); earlier versions + would produce invalid symbols and relocations on a regular basis.} + + \item{Support for thread-local storage in Mach-O.} + + \item{Support for arbitrary sections in Mach-O.} + + \item{Fix wrong negative size treated as a big positive value passed into + backend causing NASM to crash.} + + \item{Fix handling of zero-extending unsigned relocations, we have been printing + wrong message and forgot to assign segment with predefined value before + passing it into output format.} + + \item{Fix potential write of oversized (with size greater than allowed in + output format) relative relocations.} + + \item{Portability fixes for building NASM with the LLVM compiler.} + + \item{Add support of Codeview version 8 (\code{cv8}) debug format for + \code{win32} and \code{win64} formats in the \code{COFF} backend, + see \nref{codeview}.} + + \item{Allow 64-bit outputs in 16/32-bit only backends. Unsigned 64-bit + relocations are zero-extended from 32-bits with a warning + (suppressible via \code{-w-zext-reloc}); signed 64-bit relocations are + an error.} + + \item{Line numbers in list files now correspond to the lines in the source + files, instead of simply being sequential.} + + \item{There is now an official 64-bit (x64 a.k.a. x86-64) build for Windows.} +\end{itemize} + +\xsubsection{cl-2.11.09}{Version 2.11.09} + +\begin{itemize} + \item{Fix potential stack overwrite in \code{macho32} backend.} + + \item{Fix relocation records in \code{macho64} backend.} + + \item{Fix symbol lookup computation in \code{macho64} backend.} + + \item{Adjust \code{.symtab} and \code{.rela.text} sections alignments to 8 bytes + in \code{elf64} backed.} + + \item{Fix section length computation in \code{bin} backend which leaded in incorrect + relocation records.} +\end{itemize} + +\xsubsection{cl-2.11.08}{Version 2.11.08} + +\begin{itemize} + \item{Fix section length computation in \code{bin} backend which leaded in incorrect + relocation records.} + + \item{Add a warning for numeric preprocessor definitions passed via command + line which might have unexpected results otherwise.} + + \item{Add ability to specify a module name record in \code{rdoff} linker with + \code{-mn} option.} + + \item{Increase label length capacity up to 256 bytes in \code{rdoff} backend for + FreePascal sake, which tends to generate very long labels for procedures.} + + \item{Fix segmentation failure when rip addressing is used in \code{macho64} backend.} + + \item{Fix access on out of memory when handling strings with a single + grave. We have sixed similar problem in previous release but not + all cases were covered.} + + \item{Fix NULL dereference in disassembled on \code{BND} instruction.} +\end{itemize} + +\xsubsection{cl-2.11.07}{Version 2.11.07} + +\begin{itemize} + \item{Fix 256 bit \code{VMOVNTPS} instruction.} + + \item{Fix \code{-MD} option handling, which was rather broken in previous + release changing command line api.} + + \item{Fix access to unitialized space when handling strings with + a single grave.} + + \item{Fix nil dereference in handling memory reference parsing.} +\end{itemize} + +\xsubsection{cl-2.11.06}{Version 2.11.06} + +\begin{itemize} + \item{Update AVX512 instructions based on the Extension Reference (319433-021 Sept 2014).} + \item{Fix the behavior of \code{-MF} and \code{-MD} options (Bugzilla 3392280)} + \item{Updated Win32 Makefile to fix issue with build} +\end{itemize} + +\xsubsection{cl-2.11.05}{Version 2.11.05} + +\begin{itemize} + \item{Add \code{--v} as an alias for \code{-v} (see \nref{opt-v}), for + command-line compatibility with Yasm.} + \item{Fix a bug introduced in 2.11.03 whereby certain instructions would + contain multiple REX prefixes, and thus be corrupt.} +\end{itemize} + +\xsubsection{cl-2.11.04}{Version 2.11.04} + +\begin{itemize} + \item{Removed an invalid error checking code. Sometimes a memref only with + a displacement can also set an evex flag. For example: +\begin{lstlisting} +vmovdqu32 [0xabcd]{k1}, zmm0 +\end{lstlisting}} + + \item{Fixed a bug in disassembler that EVEX.L'L vector length was not matched + when EVEX.b was set because it was simply considered as EVEC.RC. + Separated EVEX.L'L case from EVEX.RC which is ignored in matching.} +\end{itemize} + +\xsubsection{cl-2.11.03}{Version 2.11.03} + +\begin{itemize} + \item{Fix a bug there REX prefixes were missing on instructions + inside a \code{TIMES} statement.} +\end{itemize} + +\xsubsection{cl-2.11.02}{Version 2.11.02} + +\begin{itemize} + \item{Add the \code{XSAVEC}, \code{XSAVES} and \code{XRSTORS} family instructions.} + \item{Add the \code{CLFLUSHOPT} instruction.} +\end{itemize} + +\xsubsection{cl-2.11.01}{Version 2.11.01} + +\begin{itemize} + \item{Allow instructions which implicitly uses \code{XMM0} (\code{VBLENDVPD}, + \code{VBLENDVPS}, \code{PBLENDVB} and \code{SHA256RNDS2}) to be specified + without an explicit \code{xmm0} on the assembly line. In other words, + the following two lines produce the same output: +\begin{lstlisting} +vblendvpd xmm2,xmm1,xmm0 ; Last operand is fixed xmm0 +vblendvpd xmm2,xmm1 ; Implicit xmm0 omitted +\end{lstlisting}} + + \item{In the ELF backends, don't crash the assembler if \code{section align} + is specified without a value.} +\end{itemize} + +\xsubsection{cl-2.11}{Version 2.11} + +\begin{itemize} + \item{Add support for the Intel AVX-512 instruction set:} + + \item{16 new, 512-bit SIMD registers. Total 32 \code{(ZMM0 \textasciitilde ZMM31)}} + + \item{8 new opmask registers \code{(K0 \textasciitilde K7)}. + One of 7 registers \code{(K1 \textasciitilde K7)} can + be used as an opmask for conditional execution.} + + \item{A new EVEX encoding prefix. EVEX is based on VEX and provides more + capabilities: opmasks, broadcasting, embedded rounding and compressed + displacements. +\begin{lstlisting} +; opmask: conditional vector operation +; using opmask k1 and {z} is for zero-masking + VDIVPD zmm0{k1}{z}, zmm1, zmm3 + +; broadcasting: load single-precision float and +; replicate it 16 times. 32 * 16 = 512 + VDIVPS zmm4, zmm5, [rbx]{1to16} + +; embedded rounding: round toward zero. note that +: it is used as if a separate operand. it comes after +; the last SIMD operand + VCVTSI2SD xmm6, xmm7, {rz-sae}, rax +\end{lstlisting}} + + \item{Add support for \code{ZWORD} (512 bits), \code{DZ} and \code{RESZ}.} + + \item{Add support for the MPX and SHA instruction sets.} + + \item{Better handling of section redefinition.} + + \item{Generate manpages when running \code{'make dist'}.} + + \item{Handle all token chains in mmacro params range.} + + \item{Support split [base,index] effective address: +\begin{lstlisting} +; eax=base, ecx=index, 4=scale, 8=disp +mov eax,[eax+8,ecx*4] +\end{lstlisting} + This is expected to be most useful for the MPX instructions.} + + \item{Support \code{BND} prefix for branch instructions (for MPX).} + + \item{The \code{DEFAULT} directive can now take \code{BND} and \code{NOBND} + options to indicate whether all relevant branches should be getting + \code{BND} prefixes. This is expected to be the normal for use in MPX + code.} + + \item{Add \code{{evex}}, \code{{vex3}} and \code{{vex2}} instruction prefixes to + have NASM encode the corresponding instruction, if possible, with an EVEX, + 3-byte VEX, or 2-byte VEX prefix, respectively.} + + \item{Support for section names longer than 8 bytes in Win32/Win64 COFF.} + + \item{The \code{NOSPLIT} directive by itself no longer forces a single + register to become an index register, unless it has an explicit + multiplier. +\begin{lstlisting} +mov eax,[nosplit eax] ; eax as base register +mov eax,[nosplit eax*1] ; eax as index register +\end{lstlisting}} +\end{itemize} + +\xsubsection{cl-2.10.09}{Version 2.10.09} + +\begin{itemize} + \item{Pregenerate man pages.} +\end{itemize} + +\xsubsection{cl-2.10.08}{Version 2.10.08} + +\begin{itemize} + \item{Fix \code{VMOVNTDQA}, \code{MOVNTDQA} and \code{MOVLPD} instructions.} + \item{Fix collision for \code{VGATHERQPS}, \code{VPGATHERQD} instructions.} + \item{Fix \code{VPMOVSXBQ}, \code{VGATHERQPD}, \code{VSPLLW} instructions.} + \item{Add a bunch of AMD TBM instructions.} + \item{Fix potential stack overwrite in numbers conversion.} + \item{Allow byte size in \code{PREFETCHTx} instructions.} + \item{Make manual pages up to date.} + \item{Make \code{F3} and \code{F2} SSE prefixes to override \code{66}.} + \item{Support of AMD SVM instructions in 32 bit mode.} + \item{Fix near offsets code generation for \code{JMP}, \code{CALL} instrictions in long mode.} + \item{Fix preprocessor parse regression when id is expanding to a whitespace.} +\end{itemize} + +\xsubsection{cl-2.10.07}{Version 2.10.07} + +\begin{itemize} + \item{Fix line continuation parsing being broken in previous version.} +\end{itemize} + +\xsubsection{cl-2.10.06}{Version 2.10.06} + +\begin{itemize} + \item{Always quote the dependency source names when using the automatic + dependency generation options.} + \item{If no dependency target name is specified via the \code{-MT} or + \code{-MQ} options, quote the default output name.} + \item{Fix assembly of shift operations in \code{CPU 8086} mode.} + \item{Fix incorrect generation of explicit immediate byte for shift by 1 + under certain circumstances.} + \item{Fix assembly of the \code{VPCMPGTQ} instruction.} + \item{Fix RIP-relative relocations in the \code{macho64} backend.} +\end{itemize} + +\xsubsection{cl-2.10.05}{Version 2.10.05} + +\begin{itemize} + \item{Add the \code{CLAC} and \code{STAC} instructions.} +\end{itemize} + +\xsubsection{cl-2.10.04}{Version 2.10.04} + +\begin{itemize} + \item{Add back the inadvertently deleted 256-bit version of the \code{VORPD} instruction.} + \item{Correct disassembly of instructions starting with byte \code{82} hex.} + \item{Fix corner cases in token pasting, for example: +\begin{lstlisting} +%define N 1e%++%+ 5 +dd N, 1e+5 +\end{lstlisting}} +\end{itemize} + +\xsubsection{cl-2.10.03}{Version 2.10.03} + +\begin{itemize} + \item{Correct the assembly of the instruction: +\begin{lstlisting} +XRELEASE MOV [absolute],AL +\end{lstlisting} + Previous versions would incorrectly generate \code{F3 A2} for this + instruction and issue a warning; correct behavior is to emit \code{F3 88 05}.} +\end{itemize} + +\xsubsection{cl-2.10.02}{Version 2.10.02} + +\begin{itemize} + \item{Add the \code{ifunc} macro package with integer functions, currently + only integer logarithms. See \nref{pkgifunc}.} + \item{Add the \code{RDSEED}, \code{ADCX} and \code{ADOX} instructions.} +\end{itemize} + +\xsubsection{cl-2.10.01}{Version 2.10.01} + +\begin{itemize} + \item{Add missing VPMOVMSKB instruction with reg32, ymmreg operands.} +\end{itemize} + +\xsubsection{cl-2.10}{Version 2.10} + +\begin{itemize} + \item{When optimization is enabled, \code{mov r64,imm} now optimizes to the + shortest form possible between: +\begin{lstlisting} +mov r32,imm32 ; 5 bytes +mov r64,imm32 ; 7 bytes +mov r64,imm64 ; 10 bytes +\end{lstlisting} + To force a specific form, use the \code{STRICT} keyword, see \nref{strict}.} + \item{Add support for the Intel AVX2 instruction set.} + \item{Add support for Bit Manipulation Instructions 1 and 2.} + \item{Add support for Intel Transactional Synchronization Extensions (TSX).} + \item{Add support for x32 ELF (32-bit ELF with the CPU in 64-bit mode.) See \nref{elffmt}.} + \item{Add support for bigendian UTF-16 and UTF-32. See \nref{unicode}.} +\end{itemize} + +\xsubsection{cl-2.09.10}{Version 2.09.10} + +\begin{itemize} + \item{Fix up NSIS script to protect uninstaller against registry keys + absence or corruption. It brings in a few additional questions + to a user during deinstallation procedure but still it is better + than unpredictable file removal.} +\end{itemize} + +\xsubsection{cl-2.09.09}{Version 2.09.09} + +\begin{itemize} + \item{Fix initialization of section attributes of \code{bin} output format.} + \item{Fix \code{mach64} output format bug that crashes NASM due to NULL symbols.} +\end{itemize} + +\xsubsection{cl-2.09.08}{Version 2.09.08} + +\begin{itemize} + \item{Fix \code{\_\_OUTPUT\_FORMAT\_\_} assignment when output driver alias + is used. For example when \code{-f elf} is used \code{\_\_OUTPUT\_FORMAT\_\_} + must be set to \code{elf}, if \code{-f elf32} is used \code{\_\_OUTPUT\_FORMAT\_\_} + must be assigned accordingly, i.e. to \code{elf32}. The rule applies to + all output driver aliases. See \nref{ofmtm}.} +\end{itemize} + +\xsubsection{cl-2.09.07}{Version 2.09.07} + +\begin{itemize} + \item{Fix attempts to close same file several times when \code{-a} option is used.} + \item{Fixes for VEXTRACTF128, VMASKMOVPS encoding.} +\end{itemize} + +\xsubsection{cl-2.09.06}{Version 2.09.06} + +\begin{itemize} + \item{Fix missed section attribute initialization in \code{bin} output target.} +\end{itemize} + +\xsubsection{cl-2.09.05}{Version 2.09.05} + +\begin{itemize} + \item{Fix arguments encoding for VPEXTRW instruction.} + \item{Remove invalid form of VPEXTRW instruction.} + \item{Add \code{VLDDQU} as alias for \code{VLDQQU} to match specification.} +\end{itemize} + +\xsubsection{cl-2.09.04}{Version 2.09.04} + +\begin{itemize} + \item{Fix incorrect labels offset for VEX intructions.} + \item{Eliminate bogus warning on implicit operand size override.} + \item{\code{\%if} term could not handle 64 bit numbers.} + \item{The COFF backend was limiting relocations number to 16 bits even if + in real there were a way more relocations.} +\end{itemize} + +\xsubsection{cl-2.09.03}{Version 2.09.03} + +\begin{itemize} + \item{Print \code{\%macro} name inside \code{\%rep} blocks on error.} + \item{Fix preprocessor expansion behaviour. It happened sometime + too early and sometime simply wrong. Move behaviour back to + the origins (down to NASM 2.05.01).} + \item{Fix unitialized data dereference on OMF output format.} + \item{Issue warning on unterminated \code{\%\{} construct.} + \item{Fix for documentation typo.} +\end{itemize} + +\xsubsection{cl-2.09.02}{Version 2.09.02} + +\begin{itemize} + \item{Fix reversed tokens when \code{\%deftok} produces more than one output token.} + \item{Fix segmentation fault on disassembling some VEX instructions.} + \item{Missing \code{\%endif} did not always cause error.} + \item{Fix typo in documentation.} + \item{Compound context local preprocessor single line macro identifiers + were not expanded early enough and as result lead to unresolved symbols.} +\end{itemize} + +\xsubsection{cl-2.09.01}{Version 2.09.01} + +\begin{itemize} + \item{Fix NULL dereference on missed \code{\%deftok} second parameter.} + \item{Fix NULL dereference on invalid \code{\%substr} parameters.} +\end{itemize} + +\xsubsection{cl-2.09}{Version 2.09} + +\begin{itemize} + \item{Fixed assignment the magnitude of \code{\%rep} counter. + It is limited to 62 bits now.} + \item{Fixed NULL dereference if argument of \code{\%strlen} resolves + to whitespace. For example if nonexistent macro parameter is used.} + \item{\code{\%ifenv}, \code{\%elifenv}, \code{\%ifnenv}, and + \code{\%elifnenv} directives introduced. See \nref{ifenv}.} + \item{Fixed NULL dereference if environment variable is missed.} + \item{Updates of new AVX v7 Intel instructions.} + \item{\code{PUSH imm32} is now officially documented.} + \item{Fix for encoding the LFS, LGS and LSS in 64-bit mode.} + \item{Fixes for compatibility with OpenWatcom compiler and DOS 8.3 file format limitation.} + \item{Macros parameters range expansion introduced. See \nref{mlmacrange}.} + \item{Backward compatibility on expanging of local sigle macros restored.} + \item{8 bit relocations for \code{elf} and \code{bin} output formats are introduced.} + \item{Short intersegment jumps are permitted now.} + \item{An alignment more than 64 bytes are allowed for \code{win32}, + \code{win64} output formats.} + \item{\code{SECTALIGN} directive introduced. See \nref{sectalign}.} + \item{\code{nojmp} option introduced in \code{smartalign} package. See + \nref{pkgsmartalign}.} + \item{Short aliases \code{win}, \code{elf} and \code{macho} for output formats are + introduced. Each stands for \code{win32}, \code{elf32} and \code{macho32} + accordingly.} + \item{Faster handling of missing directives implemented.} + \item{Various small improvements in documentation.} + \item{No hang anymore if unable to open malloc.log file.} + \item{The environments without vsnprintf function are able to build nasm again.} + \item{AMD LWP instructions updated.} + \item{Tighten EA checks. We warn a user if there overflow in EA addressing.} + \item{Make \code{-Ox} the default optimization level. For the legacy + behavior, specify \code{-O0} explicitly. See \nref{opt-O}.} + \item{Environment variables read with \code{\%!} or tested with \code{\%ifenv} + can now contain non-identifier characters if surrounded by quotes. + See \nref{getenv}.} + \item{Add a new standard macro package \code{\%use fp} for floating-point + convenience macros. See \nref{pkgfp}.} +\end{itemize} + +\xsubsection{cl-2.08.02}{Version 2.08.02} + +\begin{itemize} + \item{Fix crash under certain circumstances when using + the \code{\%+} operator.} +\end{itemize} + +\xsubsection{cl-2.08.01}{Version 2.08.01} + +\begin{itemize} + \item{Fix the \code{\%use} statement, which was broken in 2.08.} +\end{itemize} + +\xsubsection{cl-2.08}{Version 2.08} + +\begin{itemize} + \item{A number of enhancements/fixes in macros area.} + \item{Support for converting strings to tokens. See \nref{deftok}.} + \item{Fuzzy operand size logic introduced.} + \item{Fix COFF stack overrun on too long export identifiers.} + \item{Fix Macho-O alignment bug.} + \item{Fix crashes with \code{-fwin32} on file with many exports.} + \item{Fix stack overrun for too long [DEBUG id].} + \item{Fix incorrect sbyte usage in IMUL (hit only if optimization flag passed).} + \item{Append ending token for \code{.stabs} records in the ELF output format.} + \item{New NSIS script which uses ModernUI and MultiUser approach.} + \item{Visual Studio 2008 NASM integration (rules file).} + \item{Warn a user if a constant is too long (and as result will be stripped).} + \item{The obsoleted pre-XOP AMD SSE5 instruction set which was never actualized was removed.} + \item{Fix stack overrun on too long error file name passed from the command line.} + \item{Bind symbols to the .text section by default (ie in case if + \code{SECTION} directive was omitted) in the ELF output format.} + \item{Fix sync points array index wrapping.} + \item{A few fixes for FMA4 and XOP instruction templates.} + \item{Add AMD Lightweight Profiling (LWP) instructions.} + \item{Fix the offset for \code{\%arg} in 64-bit mode.} + \item{An undefined local macro (\code{\%\$}) no longer matches a global macro + with the same name.} + \item{Fix NULL dereference on too long local labels.} +\end{itemize} + +\xsubsection{cl-2.07}{Version 2.07} + +\begin{itemize} + \item{NASM is now under the 2-clause BSD license. See \nref{license}.} + \item{Fix the section type for the \code{.strtab} section in the \code{elf64} + output format.} + \item{Fix the handling of \code{COMMON} directives in the \code{obj} output format.} + \item{New \code{ith} and \code{srec} output formats; these are variants of the + \code{bin} output format which output Intel hex and Motorola S-records, + respectively. See \nref{ithfmt} and \nref{srecfmt}.} + \item{\code{rdf2ihx} replaced with an enhanced \code{rdf2bin}, which can output + binary, COM, Intel hex or Motorola S-records.} + \item{The Windows installer now puts the NASM directory first in the + \code{PATH} of the ``NASM Shell''.} + \item{Revert the early expansion behavior of \code{\%+} to + pre-2.06 behavior: \code{\%+} is only expanded late.} + \item{Yet another Mach-O alignment fix.} + \item{Don't delete the list file on errors. Also, include error and + warning information in the list file.} + \item{Support for 64-bit Mach-O output, see \nref{machofmt}.} + \item{Fix assert failure on certain operations that involve strings with + high-bit bytes.} +\end{itemize} + +\xsubsection{cl-2.06}{Version 2.06} + +\begin{itemize} + \item{This release is dedicated to the memory of Charles A. Crayne, long + time NASM developer as well as moderator of \code{comp.lang.asm.x86} and + author of the book \emph{Serious Assembler}. We miss you, Chuck.} + \item{Support for indirect macro expansion (\code{\%[...]}). See \nref{indmacro}.} + \item{\code{\%pop} can now take an argument, see \nref{pushpop}.} + \item{The argument to \code{\%use} is no longer macro-expanded. Use + \code{\%[...]} if macro expansion is desired.} + \item{Support for thread-local storage in ELF32 and ELF64. See \nref{elftls}.} + \item{Fix crash on \code{\%ifmacro} without an argument.} + \item{Correct the arguments to the \code{POPCNT} instruction.} + \item{Fix section alignment in the Mach-O format.} + \item{Update AVX support to version 5 of the Intel specification.} + \item{Fix the handling of accesses to context-local macros from higher + levels in the context stack.} + \item{Treat \code{WAIT} as a prefix rather than as an instruction, thereby + allowing constructs like \code{O16 FSAVE} to work correctly.} + \item{Support for structures with a non-zero base offset. See \nref{struc}.} + \item{Correctly handle preprocessor token concatenation (see \nref{concat}) + involving floating-point numbers.} + \item{The \code{PINSR} series of instructions have been corrected and rationalized.} + \item{Removed AMD SSE5, replaced with the new XOP/FMA4/CVT16 (rev 3.03) spec.} + \item{The ELF backends no longer automatically generate a \code{.comment} section.} + \item{Add additional "well-known" ELF sections with default attributes. See \nref{elfsect}.} +\end{itemize} + +\xsubsection{cl-2.05.01}{Version 2.05.01} + +\begin{itemize} + \item{Fix the \code{-w}/\code{-W} option parsing, which was broken in NASM 2.05.} +\end{itemize} + +\xsubsection{cl-2.05}{Version 2.05} + +\begin{itemize} + \item{Fix redundant REX.W prefix on \code{JMP reg64}.} + \item{Make the behaviour of \code{-O0} match NASM 0.98 legacy behavior. + See \nref{opt-O}.} + \item{\code{-w-user} can be used to suppress the output of \code{\%warning} directives. + See \nref{opt-w}.} + \item{Fix bug where \code{ALIGN} would issue a full alignment datum instead of + zero bytes.} + \item{Fix offsets in list files.} + \item{Fix \code{\%include} inside multi-line macros or loops.} + \item{Fix error where NASM would generate a spurious warning on valid + optimizations of immediate values.} + \item{Fix arguments to a number of the \code{CVT} SSE instructions.} + \item{Fix RIP-relative offsets when the instruction carries an immediate.} + \item{Massive overhaul of the ELF64 backend for spec compliance.} + \item{Fix the Geode \code{PFRCPV} and \code{PFRSQRTV} instruction.} + \item{Fix the SSE 4.2 \code{CRC32} instruction.} +\end{itemize} + + +\xsubsection{cl-2.04}{Version 2.04} + +\begin{itemize} + \item{Sanitize macro handing in the \code{\%error} directive.} + \item{New \code{\%warning} directive to issue user-controlled warnings.} + \item{\code{\%error} directives are now deferred to the final assembly phase.} + \item{New \code{\%fatal} directive to immediately terminate assembly.} + \item{New \code{\%strcat} directive to join quoted strings together.} + \item{New \code{\%use} macro directive to support standard macro directives. See \nref{use}.} + \item{Excess default parameters to \code{\%macro} now issues a warning by default. + See \nref{mlmacro}.} + \item{Fix \code{\%ifn} and \code{\%elifn}.} + \item{Fix nested \code{\%else} clauses.} + \item{Correct the handling of nested \code{\%rep}s.} + \item{New \code{\%unmacro} directive to undeclare a multi-line macro. + See \nref{unmacro}.} + \item{Builtin macro \code{\_\_PASS\_\_} which expands to the current assembly pass. + See \nref{passdef}.} + \item{\code{\_\_utf16\_\_} and \code{\_\_utf32\_\_} operators to generate + UTF-16 and UTF-32 strings. See \nref{unicode}.} + \item{Fix bug in case-insensitive matching when compiled on platforms that + don't use the \code{configure} script. Of the official release binaries, + that only affected the OS/2 binary.} + \item{Support for x87 packed BCD constants. See \nref{bcdconst}.} + \item{Correct the \code{LTR} and \code{SLDT} instructions in 64-bit mode.} + \item{Fix unnecessary REX.W prefix on indirect jumps in 64-bit mode.} + \item{Add AVX versions of the AES instructions (\code{VAES}...).} + \item{Fix the 256-bit FMA instructions.} + \item{Add 256-bit AVX stores per the latest AVX spec.} + \item{VIA XCRYPT instructions can now be written either with or without + \code{REP}, apparently different versions of the VIA spec wrote them + differently.} + \item{Add missing 64-bit \code{MOVNTI} instruction.} + \item{Fix the operand size of \code{VMREAD} and \code{VMWRITE}.} + \item{Numerous bug fixes, especially to the AES, AVX and VTX instructions.} + \item{The optimizer now always runs until it converges. It also runs even + when disabled, but doesn't optimize. This allows most forward references + to be resolved properly.} + \item{\code{\%push} no longer needs a context identifier; omitting the context + identifier results in an anonymous context.} +\end{itemize} + +\xsubsection{cl-2.03.01}{Version 2.03.01} + +\begin{itemize} + \item{Fix buffer overflow in the listing module.} + \item{Fix the handling of hexadecimal escape codes in `...` strings.} + \item{The Postscript/PDF documentation has been reformatted.} + \item{The \code{-F} option now implies \code{-g}.} +\end{itemize} + +\xsubsection{cl-2.03}{Version 2.03} + +\begin{itemize} + \item{Add support for Intel AVX, CLMUL and FMA instructions, + including YMM registers.} + \item{\code{dy}, \code{resy} and \code{yword} for 32-byte operands.} + \item{Fix some SSE5 instructions.} + \item{Intel \code{INVEPT}, \code{INVVPID} and \code{MOVBE} instructions.} + \item{Fix checking for critical expressions when the optimizer is enabled.} + \item{Support the DWARF debugging format for ELF targets.} + \item{Fix optimizations of signed bytes.} + \item{Fix operation on bigendian machines.} + \item{Fix buffer overflow in the preprocessor.} + \item{\code{SAFESEH} support for Win32, \code{IMAGEREL} for Win64 (SEH).} + \item{\code{\%?} and \code{\%??} to refer to the name of a macro itself. + In particular, \code{\%idefine keyword \$\%?} can be used to make + a keyword "disappear".} + \item{New options for dependency generation: \code{-MD}, \code{-MF}, + \code{-MP}, \code{-MT}, \code{-MQ}.} + \item{New preprocessor directives \code{\%pathsearch} and \code{\%depend}; + \code{INCBIN} reimplemented as a macro.} + \item{\code{\%include} now resolves macros in a sane manner.} + \item{\code{\%substr} can now be used to get other than one-character substrings.} + \item{New type of character/string constants, using backquotes (\code{`...`}), + which support C-style escape sequences.} + \item{\code{\%defstr} and \code{\%idefstr} to stringize macro definitions + before creation.} + \item{Fix forward references used in \code{EQU} statements.} +\end{itemize} + +\xsubsection{cl-2.02}{Version 2.02} + +\begin{itemize} + \item{Additional fixes for MMX operands with explicit \code{qword}, as well as + (hopefully) SSE operands with \code{oword}.} + \item{Fix handling of truncated strings with \code{DO}.} + \item{Fix segfaults due to memory overwrites when floating-point constants were used.} + \item{Fix segfaults due to missing include files.} + \item{Fix OpenWatcom Makefiles for DOS and OS/2.} + \item{Add autogenerated instruction list back into the documentation.} + \item{ELF: Fix segfault when generating stabs, and no symbols have been defined.} + \item{ELF: Experimental support for DWARF debugging information.} + \item{New compile date and time standard macros.} + \item{\code{\%ifnum} now returns true for negative numbers.} + \item{New \code{\%iftoken} test for a single token.} + \item{New \code{\%ifempty} test for empty expansion.} + \item{Add support for the \code{XSAVE} instruction group.} + \item{Makefile for Netware/gcc.} + \item{Fix issue with some warnings getting emitted way too many times.} + \item{Autogenerated instruction list added to the documentation.} +\end{itemize} + +\xsubsection{cl-2.01}{Version 2.01} + +\begin{itemize} + \item{Fix the handling of MMX registers with explicit \code{qword} tags on + memory (broken in 2.00 due to 64-bit changes.)} + \item{Fix the PREFETCH instructions.} + \item{Fix the documentation.} + \item{Fix debugging info when using \code{-f elf} + (backwards compatibility alias for \code{-f elf32}).} + \item{Man pages for rdoff tools (from the Debian project.)} + \item{ELF: handle large numbers of sections.} + \item{Fix corrupt output when the optimizer runs out of passes.} +\end{itemize} + +\xsubsection{cl-2.00}{Version 2.00} + +\begin{itemize} + \item{Added c99 data-type compliance.} + \item{Added general x86-64 support.} + \item{Added win64 (x86-64 COFF) output format.} + \item{Added \code{\_\_BITS\_\_} standard macro.} + \item{Renamed the \code{elf} output format to \code{elf32} for clarity.} + \item{Added \code{elf64} and \code{macho} (MacOS X) output formats.} + \item{Added Numeric constants in \code{dq} directive.} + \item{Added \code{oword}, \code{do} and \code{reso} pseudo operands.} + \item{Allow underscores in numbers.} + \item{Added 8-, 16- and 128-bit floating-point formats.} + \item{Added binary, octal and hexadecimal floating-point.} + \item{Correct the generation of floating-point constants.} + \item{Added floating-point option control.} + \item{Added Infinity and NaN floating point support.} + \item{Added ELF Symbol Visibility support.} + \item{Added setting OSABI value in ELF header directive.} + \item{Added Generate Makefile Dependencies option.} + \item{Added Unlimited Optimization Passes option.} + \item{Added \code{\%ifn} and \code{\%elifn} support.} + \item{Added Logical Negation Operator.} + \item{Enhanced Stack Relative Preprocessor Directives.} + \item{Enhanced ELF Debug Formats.} + \item{Enhanced Send Errors to a File option.} + \item{Added SSSE3, SSE4.1, SSE4.2, SSE5 support.} + \item{Added a large number of additional instructions.} + \item{Significant performance improvements.} + \item{\code{-w+warning} and \code{-w-warning} can now be written + as -Wwarning and -Wno-warning, respectively. See \nref{opt-w}.} + \item{Add \code{-w+error} to treat warnings as errors. See \nref{opt-w}.} + \item{Add \code{-w+all} and \code{-w-all} to enable or disable all suppressible + warnings. See \nref{opt-w}.} +\end{itemize} + +\xsection{cl-0.98.xx}{NASM 0.98 Series} + +The 0.98 series was the production versions of NASM from 1999 to 2007. + +\xsubsection{cl-0.98.39}{Version 0.98.39} + +\begin{itemize} + \item{fix buffer overflow} + \item{fix outas86's \code{.bss} handling} + \item{"make spotless" no longer deletes config.h.in.} + \item{\code{\%(el)if(n)idn} insensitivity to string quotes difference (\#809300).} + \item{(nasm.c)\code{\_\_OUTPUT\_FORMAT\_\_} changed to string value instead of symbol.} +\end{itemize} + +\xsubsection{cl-0.98.38}{Version 0.98.38} + +\begin{itemize} + \item{Add Makefile for 16-bit DOS binaries under OpenWatcom, and modify + \code{mkdep.pl} to be able to generate completely pathless dependencies, as + required by OpenWatcom wmake (it supports path searches, but not + explicit paths.)} + \item{Fix the \code{STR} instruction.} + \item{Fix the ELF output format, which was broken under certain + circumstances due to the addition of stabs support.} + \item{Quick-fix Borland format debug-info for \code{-f obj}} + \item{Fix for \code{\%rep} with no arguments (\#560568)} + \item{Fix concatenation of preprocessor function call (\#794686)} + \item{Fix long label causes coredump (\#677841)} + \item{Use autoheader as well as autoconf to keep configure from generating + ridiculously long command lines.} + \item{Make sure that all of the formats which support debugging output + actually will suppress debugging output when \code{-g} not specified.} +\end{itemize} + +\xsubsection{cl-0.98.37}{Version 0.98.37} + +\begin{itemize} + \item{Paths given in \code{-I} switch searched for \code{incbin}-ed as + well as \code{\%include}-ed files.} + \item{Added stabs debugging for the ELF output format, patch from + Martin Wawro.} + \item{Fix \code{output/outbin.c} to allow origin > 80000000h.} + \item{Make \code{-U} switch work.} + \item{Fix the use of relative offsets with explicit prefixes, e.g. + \code{a32 loop foo}.} + \item{Remove \code{backslash()}.} + \item{Fix the \code{SMSW} and \code{SLDT} instructions.} + \item{\code{-O2} and \code{-O3} are no longer aliases for \code{-O10} and \code{-O15}. + If you mean the latter, please say so! :)} +\end{itemize} + +\xsubsection{cl-0.98.36}{Version 0.98.36} + +\begin{itemize} + \item{Update rdoff - librarian/archiver - common rec - docs!} + \item{Fix signed/unsigned problems.} + \item{Fix \code{JMP FAR label} and \code{CALL FAR label}.} + \item{Add new multisection support - map files - fix align bug} + \item{Fix sysexit, movhps/movlps reg,reg bugs in insns.dat} + \item{\code{Q} or \code{O} suffixes indicate octal} + \item{Support Prescott new instructions (PNI).} + \item{Cyrix \code{XSTORE} instruction.} +\end{itemize} + + +\xsubsection{cl-0.98.35}{Version 0.98.35} + +\begin{itemize} + \item{Fix build failure on 16-bit DOS (Makefile.bc3 workaround for compiler bug.)} + \item{Fix dependencies and compiler warnings.} + \item{Add "const" in a number of places.} + \item{Add -X option to specify error reporting format (use -Xvc to + integrate with Microsoft Visual Studio.)} + \item{Minor changes for code legibility.} + \item{Drop use of tmpnam() in rdoff (security fix.)} +\end{itemize} + +\xsubsection{cl-0.98.34}{Version 0.98.34} + +\begin{itemize} + \item{Correct additional address-size vs. operand-size confusions.} + \item{Generate dependencies for all Makefiles automatically.} + \item{Add support for unimplemented (but theoretically available) + registers such as tr0 and cr5. Segment registers 6 and 7 are called + segr6 and segr7 for the operations which they can be represented.} + \item{Correct some disassembler bugs related to redundant address-size prefixes. + Some work still remains in this area.} + \item{Correctly generate an error for things like "SEG eax".} + \item{Add the JMPE instruction, enabled by "CPU IA64".} + \item{Correct compilation on newer gcc/glibc platforms.} + \item{Issue an error on things like "jmp far eax".} +\end{itemize} + +\xsubsection{cl-0.98.33}{Version 0.98.33} + +\begin{itemize} + \item{New \_\_NASM\_PATCHLEVEL\_\_ and \_\_NASM\_VERSION\_ID\_\_ standard macros + to round out the version-query macros. version.pl now understands + X.YYplWW or X.YY.ZZplWW as a version number, equivalent to + X.YY.ZZ.WW (or X.YY.0.WW, as appropriate).} + \item{New keyword "strict" to disable the optimization of specific operands.} + \item{Fix the handing of size overrides with JMP instructions + (instructions such as "jmp dword foo".)} + \item{Fix the handling of "ABSOLUTE label", where "label" points into a + relocatable segment.} + \item{Fix OBJ output format with lots of externs.} + \item{More documentation updates.} + \item{Add -Ov option to get verbose information about optimizations.} + \item{Undo a braindead change which broke \code{\%elif} directives.} + \item{Makefile updates.} +\end{itemize} + +\xsubsection{cl-0.98.32}{Version 0.98.32} + +\begin{itemize} + \item{Fix NASM crashing when \code{\%macro} directives were left unterminated.} + \item{Lots of documentation updates.} + \item{Complete rewrite of the PostScript/PDF documentation generator.} + \item{The MS Visual C++ Makefile was updated and corrected.} + \item{Recognize .rodata as a standard section name in ELF.} + \item{Fix some obsolete Perl4-isms in Perl scripts.} + \item{Fix configure.in to work with autoconf 2.5x.} + \item{Fix a couple of "make cleaner" misses.} + \item{Make the normal "./configure \&\& make" work with Cygwin.} +\end{itemize} + +\xsubsection{cl-0.98.31}{Version 0.98.31} + +\begin{itemize} + \item{Correctly build in a separate object directory again.} + \item{Derive all references to the version number from the version file.} + \item{New standard macros \code{\_\_NASM\_SUBMINOR\_\_} and + \code{\_\_NASM\_VER\_\_} macros.} + \item{Lots of Makefile updates and bug fixes.} + \item{New \code{\%ifmacro} directive to test for multiline macros.} + \item{Documentation updates.} + \item{Fixes for 16-bit OBJ format output.} + \item{Changed the NASM environment variable to NASMENV.} +\end{itemize} + +\xsubsection{cl-0.98.30}{Version 0.98.30} + +\begin{itemize} + \item{Changed doc files a lot: completely removed old READMExx and + Wishlist files, incorporating all information in CHANGES and TODO.} + \item{I waited a long time to rename zoutieee.c to (original) outieee.c} + \item{moved all output modules to output/ subdirectory.} + \item{Added 'make strip' target to strip debug info from nasm \& ndisasm.} + \item{Added INSTALL file with installation instructions.} + \item{Added -v option description to nasm man.} + \item{Added dist makefile target to produce source distributions.} + \item{16-bit support for ELF output format (GNU extension, but useful.)} +\end{itemize} + + +\xsubsection{cl-0.98.28}{Version 0.98.28} + +\begin{itemize} + \item{Fastcooked this for Debian's Woody release: + Frank applied the \code{INCBIN} bug patch to 0.98.25alt + and called it 0.98.28 to not confuse poor little apt-get.} +\end{itemize} + +\xsubsection{cl-0.98.26}{Version 0.98.26} + +\begin{itemize} + \item{Reorganised files even better from 0.98.25alt} +\end{itemize} + + +\xsubsection{cl-0.98.25alt}{Version 0.98.25alt} + +\begin{itemize} + \item{Prettified the source tree. Moved files to more reasonable places.} + \item{Added findleak.pl script to misc/ directory.} + \item{Attempted to fix doc.} +\end{itemize} + +\xsubsection{cl-0.98.25}{Version 0.98.25} + +\begin{itemize} + \item{Line continuation character \code{\\}.} + \item{Docs inadvertantly reverted - "dos packaging".} +\end{itemize} + + +\xsubsection{cl-0.98.24p1}{Version 0.98.24p1} + +\begin{itemize} + \item{FIXME: Someone, document this please.} +\end{itemize} + +\xsubsection{cl-0.98.24}{Version 0.98.24} + +\begin{itemize} + \item{Documentation - Ndisasm doc added to Nasm.doc.} +\end{itemize} + +\xsubsection{cl-0.98.23}{Version 0.98.23} + +\begin{itemize} + \item{Attempted to remove rdoff version1} + \item{Lino Mastrodomenico's patches to preproc.c (\%\$\$ bug?).} +\end{itemize} + + +\xsubsection{cl-0.98.22}{Version 0.98.22} + +\begin{itemize} + \item{Update rdoff2 - attempt to remove v1.} +\end{itemize} + +\xsubsection{cl-0.98.21}{Version 0.98.21} + +\begin{itemize} + \item{Optimization fixes.} +\end{itemize} + +\xsubsection{cl-0.98.20}{Version 0.98.20} + +\begin{itemize} + \item{Optimization fixes.} +\end{itemize} + +\xsubsection{cl-0.98.19}{Version 0.98.19} + +\begin{itemize} + \item{H. J. Lu's patch back out.} +\end{itemize} + +\xsubsection{cl-0.98.18}{Version 0.98.18} + +\begin{itemize} + \item{Added ".rdata" to "-f win32".} +\end{itemize} + +\xsubsection{cl-0.98.17}{Version 0.98.17} + +\begin{itemize} + \item{H. J. Lu's "bogus elf" patch. (Red Hat problem?)} +\end{itemize} + + +\xsubsection{cl-0.98.16}{Version 0.98.16} + +\begin{itemize} + \item{Fix whitespace before \code{[section \dots]} bug.} +\end{itemize} + +\xsubsection{cl-0.98.15}{Version 0.98.15} + +\begin{itemize} + \item{Rdoff changes (?).} + \item{Fix fixes to memory leaks.} +\end{itemize} + +\xsubsection{cl-0.98.14}{Version 0.98.14} + +\begin{itemize} + \item{Fix memory leaks.} +\end{itemize} + +\xsubsection{cl-0.98.13}{Version 0.98.13} + +\begin{itemize} + \item{There was no 0.98.13} +\end{itemize} + + +\xsubsection{cl-0.98.12}{Version 0.98.12} + +\begin{itemize} + \item{Update optimization (new function of \code{-O1}).} + \item{Changes to test/bintest.asm (?).} +\end{itemize} + +\xsubsection{cl-0.98.11}{Version 0.98.11} + +\begin{itemize} + \item{Optimization changes.} + \item{Ndisasm fixed.} +\end{itemize} + +\xsubsection{cl-0.98.10}{Version 0.98.10} + +\begin{itemize} + \item{There was no 0.98.10} +\end{itemize} + +\xsubsection{cl-0.98.09}{Version 0.98.09} + +\begin{itemize} + \item{Add multiple sections support to \code{-f bin}.} + \item{Changed \code{GLOBAL\_TEMP\_BASE} in outelf.c from 6 to 15.} + \item{Add \code{-v} as an alias to the \code{-r} switch.} + \item{Remove \code{\#ifdef} from Tasm compatibility options.} + \item{Remove redundant size-overrides on \code{mov ds, ex}, etc.} + \item{Fixes to SSE2, other insns.dat (?).} + \item{Enable uppercase "I" and "P" switches.} + \item{Case insinsitive \code{seg} and \code{wrt}.} + \item{Update install.sh (?).} + \item{Allocate tokens in blocks.} + \item{Improve "invalid effective address" messages.} +\end{itemize} + +\xsubsection{cl-0.98.08}{Version 0.98.08} + +\begin{itemize} + \item{Add \code{\%strlen} and \code{\%substr} macro operators.} + \item{Fixed broken c16.mac.} + \item{Unterminated string error reported.} + \item{Fixed bugs as per 0.98bf} +\end{itemize} + +\xsubsection{cl-0.98.09b}{Version 0.98.09b with John Coffman patches released 28-Oct-2001} + +Changes from 0.98.07 release to 98.09b as of 28-Oct-2001 + +\begin{itemize} + \item{More closely compatible with 0.98 when \code{-O0} is implied + or specified. Not strictly identical, since backward + branches in range of short offsets are recognized, and signed + byte values with no explicit size specification will be + assembled as a single byte.} + \item{More forgiving with the PUSH instruction. 0.98 requires + a size to be specified always. 0.98.09b will imply the size + from the current BITS setting (16 or 32).} + \item{Changed definition of the optimization flag + \begin{itemize} + \item{\code{-O0}: strict two-pass assembly, JMP and Jcc are + handled more like 0.98, except that back ward JMPs are + short, if possible.} + \item{\code{-O1}: strict two-pass assembly, but forward + branches are assembled with code guaranteed + to reach; may produce larger code than + \code{-O0}, but will produce successful assembly + more often if branch offset sizes are not + specified.} + \item{\code{-O2}: multi-pass optimization, minimize branch + offsets; also will minimize signed immediate bytes, + overriding size specification.} + \item{\code{-O3}: like \code{-O2}, but more passes taken, + if needed} + \end{itemize}} +\end{itemize} + +\xsubsection{cl-0.98.07}{Version 0.98.07 released 01/28/01} + +\begin{itemize} + \item{Added Stepane Denis' SSE2 instructions to a \emph{working} + version of the code - some earlier versions were based on + broken code - sorry 'bout that. version "0.98.07"} + \item{Cosmetic modifications to nasm.c, nasm.h, AUTHORS, MODIFIED} +\end{itemize} + +\xsubsection{cl-0.98.06f}{Version 0.98.06f released 01/18/01} + +\begin{itemize} + \item{Add "metalbrain"s jecxz bug fix in insns.dat} + \item{Alter nasmdoc.src to match - version "0.98.06f"} +\end{itemize} + +\xsubsection{cl-0.98.06e}{Version 0.98.06e released 01/09/01} + +\begin{itemize} + \item{Removed the "outforms.h" file - it appears to be + someone's old backup of "outform.h". version "0.98.06e"} + \item{fbk - finally added the fix for the "multiple \code{\%include} bug", + known since 7/27/99 - reported originally (?) and sent to + us by Austin Lunnen - he reports that John Fine had a fix + within the day. Here it is...} + \item{Nelson Rush resigns from the group. Big thanks to Nelson for + his leadership and enthusiasm in getting these changes + incorporated into Nasm!} + \item{fbk - \code{[list +]}, \code{[list -]} directives - ineptly implemented, + should be re-written or removed, perhaps.} + \item{Brian Raiter / fbk - "elfso bug" fix - applied to aoutb format + as well - testing might be desirable...} + \item{James Seter - -postfix, -prefix command line switches.} + \item{Yuri Zaporozhets - rdoff utility changes.} +\end{itemize} + +\xsubsection{cl-0.98p1}{Version 0.98p1} + +\begin{itemize} + \item{GAS-like palign (Panos Minos)} + \item{FIXME: Someone, fill this in with details} +\end{itemize} + +\xsubsection{cl-0.98bf}{Version 0.98bf (bug-fixed)} + +\begin{itemize} + \item{Fixed - elf and aoutb bug - shared libraries} + \item{multiple \code{\%include} bug in "-f obj"} + \item{jcxz, jecxz bug} + \item{unrecognized option bug in ndisasm} +\end{itemize} + +\xsubsection{cl-0.98.03}{Version 0.98.03 with John Coffman's changes released 27-Jul-2000} + +\begin{itemize} + \item{Added signed byte optimizations for the 0x81/0x83 class + of instructions: ADC, ADD, AND, CMP, OR, SBB, SUB, XOR: + when used as 'ADD reg16,imm' or 'ADD reg32,imm.' Also + optimization of signed byte form of 'PUSH imm' and 'IMUL + reg,imm'/'IMUL reg,reg,imm.' No size specification is needed.} + \item{Added multi-pass JMP and Jcc offset optimization. Offsets + on forward references will preferentially use the short form, + without the need to code a specific size (short or near) for + the branch. Added instructions for 'Jcc label' to use the + form 'Jnotcc \$+3/JMP label', in cases where a short offset + is out of bounds. If compiling for a 386 or higher CPU, then + the 386 form of Jcc will be used instead. + + This feature is controlled by a new command-line switch: "O", + (upper case letter O). "-O0" reverts the assembler to no + extra optimization passes, "-O1" allows up to 5 extra passes, + and "-O2"(default), allows up to 10 extra optimization passes.} + \item{Added a new directive: 'cpu XXX', where XXX is any of: + 8086, 186, 286, 386, 486, 586, pentium, 686, PPro, P2, P3 or + Katmai. All are case insensitive. All instructions will + be selected only if they apply to the selected cpu or lower. + Corrected a couple of bugs in cpu-dependence in 'insns.dat'.} + \item{Added to 'standard.mac', the "use16" and "use32" forms of + the "bits 16/32" directive. This is nothing new, just conforms + to a lot of other assemblers. (minor)} + \item{Changed label allocation from 320/32 (10000 labels @ 200K+) + to 32/37 (1000 labels); makes running under DOS much easier. + Since additional label space is allocated dynamically, this + should have no effect on large programs with lots of labels. + The 37 is a prime, believed to be better for hashing. (minor)} +\end{itemize} + +\xsubsection{cl-0.98.03}{Version 0.98.03} + +"Integrated patchfile 0.98-0.98.01. I call this version 0.98.03 for +historical reasons: 0.98.02 was trashed." --John Coffman +<johninsd@san.rr.com>, 27-Jul-2000 + +\begin{itemize} + \item{Kendall Bennett's SciTech MGL changes} + \item{Note that you must define "TASM\_COMPAT" at compile-time + to get the Tasm Ideal Mode compatibility.} + \item{All changes can be compiled in and out using the TASM\_COMPAT macros, + and when compiled without TASM\_COMPAT defined we get the exact same + binary as the unmodified 0.98 sources.} + \item{standard.mac, macros.c: Added macros to ignore TASM directives before + first include} + \item{nasm.h: Added extern declaration for tasm\_compatible\_mode} + \item{nasm.c: Added global variable tasm\_compatible\_mode} + \item{Added command line switch for TASM compatible mode (-t)} + \item{Changed version command line to reflect when compiled with TASM additions} + \item{Added response file processing to allow all arguments on a single + line (response file is @resp rather than -@resp for NASM format).} + \item{labels.c: Changes islocal() macro to support TASM style @@local labels.} + \item{Added islocalchar() macro to support TASM style @@local labels.} + \item{parser.c: Added support for TASM style memory references (ie: mov + [DWORD eax],10 rather than the NASM style mov DWORD [eax],10).} + \item{preproc.c: Added new directives, \code{\%arg}, \code{\%local}, + \code{\%stacksize} to directives table} + \item{Added support for TASM style directives without a leading \% symbol.} + \item{Integrated a block of changes from Andrew Zabolotny <bit@eltech.ru>:} + \item{A new keyword \code{\%xdefine} and its case-insensitive counterpart + \code{\%ixdefine}. They work almost the same way as \code{\%define} and + \code{\%idefine} but expand the definition immediately, not on the invocation. + Something like a cross between \code{\%define} and \code{\%assign}. The "x" + suffix stands for "eXpand", so "xdefine" can be deciphered as "expand-and-define". + Thus you can do things like this: +\begin{lstlisting} +%assign ofs 0 + +%macro arg 1 + %xdefine %1 dword [esp+ofs] + %assign ofs ofs+4 +%endmacro +\end{lstlisting}} + \item{Changed the place where the expansion of \%\$name macros are expanded. + Now they are converted into ..@ctxnum.name form when detokenizing, so + there are no quirks as before when using \%\$name arguments to macros, + in macros etc. For example: +\begin{lstlisting} +%macro abc 1 + %define %1 hello +%endm + abc %$here +%$here +\end{lstlisting} + Now last line will be expanded into "hello" as expected. This also allows + for lots of goodies, a good example are extended "proc" macros included + in this archive.} + + \item{Added a check for "cstk" in smacro\_defined() before calling get\_ctx() - + this allows for things like: +\begin{lstlisting} +%ifdef %$abc +%endif +\end{lstlisting} + work without warnings even in no context.} + \item{Added a check for "cstk" in \%if*ctx and \%elif*ctx directives - + this allows to use \code{\%ifctx} without excessive warnings. If there is + no active context, \code{\%ifctx} goes through "false" branch.} + \item{Removed "user error: " prefix with \code{\%error} directive: it just clobbers the + output and has absolutely no functionality. Besides, this allows to write + macros that does not differ from built-in functions in any way.} + \item{Added expansion of string that is output by \code{\%error} directive. Now you + can do things like: +\begin{lstlisting} +%define hello(x) Hello, x! + +%define %$name andy +%error "hello(%$name)" +\end{lstlisting} + Same happened with \code{\%include} directive.} + \item{Now all directives that expect an identifier will try to expand and + concatenate everything without whitespaces in between before usage. + For example, with "unfixed" nasm the commands +\begin{lstlisting} +%define %$abc hello +%define __%$abc goodbye +__%$abc +\end{lstlisting} + would produce "incorrect" output: last line will expand to +\begin{lstlisting} +hello goodbyehello +\end{lstlisting} + Not quite what you expected, eh? :-) The answer is that preprocessor + treats the \code{\%define} construct as if it would be +\begin{lstlisting} +%define __ %$abc goodbye +\end{lstlisting} + (note the white space between \_\_ and \%\$abc). After my "fix" it + will "correctly" expand into +\begin{lstlisting} +goodbye +\end{lstlisting} + as expected. Note that I use quotes around words "correct", "incorrect" + etc because this is rather a feature not a bug; however current behaviour + is more logical (and allows more advanced macro usage :-). + + Same change was applied to: \code{\%push},\code{\%macro},\code{\%imacro}, + \code{\%define},\code{\%idefine},\code{\%xdefine},\code{\%ixdefine}, + \code{\%assign},\code{\%iassign},\code{\%undef}} + \item{A new directive \code{[WARNING {+|-}warning-id]} have been added. It works only + if the assembly phase is enabled (i.e. it doesn't work with nasm -e).} + \item{A new warning type: macro-selfref. By default this warning is disabled; + when enabled NASM warns when a macro self-references itself; for example + the following source: +\begin{lstlisting} +[WARNING macro-selfref] +%macro push 1-* + %rep %0 + push %1 + %rotate 1 + %endrep +%endmacro + + push eax,ebx,ecx +\end{lstlisting} + will produce a warning, but if we remove the first line we won't see it + anymore (which is The Right Thing To Do \texttrademark IMHO since C + preprocessor eats such constructs without warnings at all).} + \item{Added a "error" routine to preprocessor which always will set ERR\_PASS1 + bit in severity\_code. This removes annoying repeated errors on first + and second passes from preprocessor.} + \item{Added the \%+ operator in single-line macros for concatenating two + identifiers. Usage example: +\begin{lstlisting} +%define _myfunc _otherfunc +%define cextern(x) _ %+ x +cextern (myfunc) +\end{lstlisting} + After first expansion, third line will become "\_myfunc". After this + expansion is performed again so it becomes "\_otherunc".} + \item{Now if preprocessor is in a non-emitting state, no warning or error + will be emitted. Example: +\begin{lstlisting} +%if 1 + mov eax,ebx +%else + put anything you want between these two brackets, + even macro-parameter references %1 or local + labels %$zz or macro-local labels %%zz - no + warning will be emitted. +%endif +\end{lstlisting}} + \item{Context-local variables on expansion as a last resort are looked up + in outer contexts. For example, the following piece: +\begin{lstlisting} +%push outer +%define %$a [esp] + + %push inner + %$a + %pop +%pop +\end{lstlisting} + will expand correctly the fourth line to [esp]; if we'll define another + \%\$a inside the "inner" context, it will take precedence over outer + definition. However, this modification has been applied only to + expand\_smacro and not to smacro\_define: as a consequence expansion + looks in outer contexts, but \code{\%ifdef} won't look in outer contexts. + + This behaviour is needed because we don't want nested contexts to + act on already defined local macros. Example: +\begin{lstlisting} +%define %$arg1 [esp+4] +test eax,eax +if nz + mov eax,%$arg1 +endif +\end{lstlisting} + In this example the "if" mmacro enters into the "if" context, so \%\$arg1 + is not valid anymore inside "if". Of course it could be worked around + by using explicitely \%\$\$arg1 but this is ugly IMHO.} + \item{Fixed memory leak in \code{\%undef}. The origline wasn't freed before exiting on success.} + \item{Fixed trap in preprocessor when line expanded to empty set of tokens. + This happens, for example, in the following case: +\begin{lstlisting} +#define SOMETHING +SOMETHING +\end{lstlisting}} +\end{itemize} + +\xsubsection{cl-0.98}{Version 0.98} + +All changes since NASM 0.98p3 have been produced by H. Peter Anvin <hpa@zytor.com>. + +\begin{itemize} + \item{The documentation comment delimiter is \code{\textbackslash \#} not \code{\#}.} + \item{Allow EQU definitions to refer to external labels; reported by Pedro Gimeno.} + \item{Re-enable support for RDOFF v1; reported by Pedro Gimeno.} + \item{Updated License file per OK from Simon and Julian.} +\end{itemize} + +\xsubsection{cl-0.98p9}{Version 0.98p9} + +\begin{itemize} + \item{Update documentation (although the instruction set reference will + have to wait; I don't want to hold up the 0.98 release for it.)} + \item{Verified that the NASM implementation of the PEXTRW and PMOVMSKB + instructions is correct. The encoding differs from what the Intel + manuals document, but the Pentium III behaviour matches NASM, not + the Intel manuals.} + \item{Fix handling of implicit sizes in PSHUFW and PINSRW, reported by + Stefan Hoffmeister.} + \item{Resurrect the -s option, which was removed when changing the + diagnostic output to stdout.} +\end{itemize} + +\xsubsection{cl-0.98p8}{Version 0.98p8} + +\begin{itemize} + \item{Fix for "DB" when NASM is running on a bigendian machine.} + \item{Invoke insns.pl once for each output script, making Makefile.in + legal for "make -j".} + \item{Improve the Unix configure-based makefiles to make package + creation easier.} + \item{Included an RPM .spec file for building RPM (RedHat Package Manager) + packages on Linux or Unix systems.} + \item{Fix Makefile dependency problems.} + \item{Change src/rdsrc.pl to include sectioning information in info + output; required for install-info to work.} + \item{Updated the RDOFF distribution to version 2 from Jules; minor + massaging to make it compile in my environment.} + \item{Split doc files that can be built by anyone with a Perl interpreter off + into a separate archive.} + \item{"Dress rehearsal" release!} +\end{itemize} + +\xsubsection{cl-0.98p7}{Version 0.98p7} + +\begin{itemize} + \item{Fixed opcodes with a third byte-sized immediate argument to not + complain if given "byte" on the immediate.} + \item{Allow \code{\%undef} to remove single-line macros with arguments. This + matches the behaviour of \#undef in the C preprocessor.} + \item{Allow -d, -u, -i and -p to be specified as -D, -U, -I and -P for + compatibility with most C compilers and preprocessors. This allows + Makefile options to be shared between cc and nasm, for example.} + \item{Minor cleanups.} + \item{Went through the list of Katmai instructions and hopefully fixed the + (rather few) mistakes in it.} + \item{(Hopefully) fixed a number of disassembler bugs related to ambiguous + instructions (disambiguated by -p) and SSE instructions with REP.} + \item{Fix for bug reported by Mark Junger: "call dword 0x12345678" should + work and may add an OSP (affected CALL, JMP, Jcc).} + \item{Fix for environments when "stderr" isn't a compile-time constant.} +\end{itemize} + +\xsubsection{cl-0.98p6}{Version 0.98p6} + +\begin{itemize} + \item{Took officially over coordination of the 0.98 release; so drop + the p3.x notation. Skipped p4 and p5 to avoid confusion with John + Fine's J4 and J5 releases.} + \item{Update the documentation; however, it still doesn't include + documentation for the various new instructions. I somehow wonder if + it makes sense to have an instruction set reference in the assembler + manual when Intel et al have PDF versions of their manuals online.} + \item{Recognize "idt" or "centaur" for the -p option to ndisasm.} + \item{Changed error messages back to stderr where they belong, but add an + -E option to redirect them elsewhere (the DOS shell cannot redirect + stderr.)} + \item{-M option to generate Makefile dependencies (based on code from Alex Verstak.)} + \item{\code{\%undef} preprocessor directive, and -u option, that undefines a + single-line macro.} + \item{OS/2 Makefile (Mkfiles/Makefile.os2) for Borland under OS/2; from + Chuck Crayne.} + \item{Various minor bugfixes (reported by): + - Dangling \code{\%s} in preproc.c (Martin Junker)} + \item{THERE ARE KNOWN BUGS IN SSE AND THE OTHER KATMAI INSTRUCTIONS. I am + on a trip and didn't bring the Katmai instruction reference, so I + can't work on them right now.} + \item{Updated the License file per agreement with Simon and Jules to + include a GPL distribution clause.} +\end{itemize} + +\xsubsection{cl-0.98p3.7}{Version 0.98p3.7} + +\begin{itemize} + \item{(Hopefully) fixed the canned Makefiles to include the outrdf2 and + zoutieee modules.} + \item{Renamed changes.asm to changed.asm.} +\end{itemize} + +\xsubsection{cl-0.98p3.6}{Version 0.98p3.6} + +\begin{itemize} + \item{Fixed a bunch of instructions that were added in 0.98p3.5 which had + memory operands, and the address-size prefix was missing from the + instruction pattern.} +\end{itemize} + +\xsubsection{cl-0.98p3.5}{Version 0.98p3.5} + +\begin{itemize} + \item{Merged in changes from John S. Fine's 0.98-J5 release. John's based + 0.98-J5 on my 0.98p3.3 release; this merges the changes.} + \item{Expanded the instructions flag field to a long so we can fit more + flags; mark SSE (KNI) and AMD or Katmai-specific instructions as + such.} + \item{Fix the "PRIV" flag on a bunch of instructions, and create new + "PROT" flag for protected-mode-only instructions (orthogonal to if + the instruction is privileged!) and new "SMM" flag for SMM-only + instructions.} + \item{Added AMD-only SYSCALL and SYSRET instructions.} + \item{Make SSE actually work, and add new Katmai MMX instructions.} + \item{Added a -p (preferred vendor) option to ndisasm so that it can + distinguish e.g. Cyrix opcodes also used in SSE. For example: +\begin{lstlisting} +ndisasm -p cyrix aliased.bin +00000000 670F514310 paddsiw mm0,[ebx+0x10] +00000005 670F514320 paddsiw mm0,[ebx+0x20] +ndisasm -p intel aliased.bin +00000000 670F514310 sqrtps xmm0,[ebx+0x10] +00000005 670F514320 sqrtps xmm0,[ebx+0x20] +\end{lstlisting}} + \item{Added a bunch of Cyrix-specific instructions.} +\end{itemize} + +\xsubsection{cl-0.98p3.4}{Version 0.98p3.4} + +\begin{itemize} + \item{Made at least an attempt to modify all the additional Makefiles (in + the Mkfiles directory). I can't test it, but this was the best I + could do.} + \item{DOS DJGPP+"Opus Make" Makefile from John S. Fine.} + \item{changes.asm changes from John S. Fine.} +\end{itemize} + +\xsubsection{cl-0.98p3.3}{Version 0.98p3.3} + +\begin{itemize} + \item{Patch from Conan Brink to allow nesting of \code{\%rep} directives.} + \item{If we're going to allow INT01 as an alias for INT1/ICEBP (one of + Jules 0.98p3 changes), then we should allow INT03 as an alias for INT3 + as well.} + \item{Updated changes.asm to include the latest changes.} + \item{Tried to clean up the <CR>s that had snuck in from a DOS/Windows + environment into my Unix environment, and try to make sure than + DOS/Windows users get them back.} + \item{We would silently generate broken tools if insns.dat wasn't sorted + properly. Change insns.pl so that the order doesn't matter.} + \item{Fix bug in insns.pl (introduced by me) which would cause conditional + instructions to have an extra "cc" in disassembly, e.g. "jnz" + disassembled as "jccnz".} +\end{itemize} + +\xsubsection{cl-0.98p3.2}{Version 0.98p3.2} + +\begin{itemize} + \item{Merged in John S. Fine's changes from his 0.98-J4 prerelease; see + http://www.csoft.net/cz/johnfine/} + \item{Changed previous "spotless" Makefile target (appropriate for distribution) + to "distclean", and added "cleaner" target which is same as "clean" + except deletes files generated by Perl scripts; "spotless" is union.} + \item{Removed BASIC programs from distribution. Get a Perl interpreter + instead (see below.)} + \item{Calling this "pre-release 3.2" rather than "p3-hpa2" because of + John's contributions.} + \item{Actually link in the IEEE output format (zoutieee.c); fix a bunch of + compiler warnings in that file. Note I don't know what IEEE output + is supposed to look like, so these changes were made "blind".} +\end{itemize} + +\xsubsection{cl-0.98p3-hpa}{Version 0.98p3-hpa} + +\begin{itemize} + \item{Merged nasm098p3.zip with nasm-0.97.tar.gz to create a fully + buildable version for Unix systems (Makefile.in updates, etc.)} + \item{Changed insns.pl to create the instruction tables in nasm.h and + names.c, so that a new instruction can be added by adding it *only* + to insns.dat.} + \item{Added the following new instructions: SYSENTER, SYSEXIT, FXSAVE, + FXRSTOR, UD1, UD2 (the latter two are two opcodes that Intel + guarantee will never be used; one of them is documented as UD2 in + Intel documentation, the other one just as "Undefined Opcode" -- + calling it UD1 seemed to make sense.)} + \item{MAX\_SYMBOL was defined to be 9, but LOADALL286 and LOADALL386 are 10 + characters long. Now MAX\_SYMBOL is derived from insns.dat.} + \item{A note on the BASIC programs included: forget them. insns.bas is + already out of date. Get yourself a Perl interpreter for your + platform of choice at \href{http://www.cpan.org/ports/index.html} + {http://www.cpan.org/ports/index.html}.} +\end{itemize} + +\xsubsection{cl-0.98p3}{Version 0.98 pre-release 3} + +\begin{itemize} + \item{added response file support, improved command line handling, + new layout help screen} + \item{fixed limit checking bug, 'OUT byte nn, reg' bug, and + a couple of rdoff related bugs, updated Wishlist; 0.98 Prerelease 3.} +\end{itemize} + +\xsubsection{cl-0.98p2}{Version 0.98 pre-release 2} + +\begin{itemize} + \item{fixed bug in outcoff.c to do with truncating section names longer + than 8 characters, referencing beyond end of string; 0.98 pre-release 2} +\end{itemize} + +\xsubsection{cl-0.98p1}{Version 0.98 pre-release 1} + +\begin{itemize} + \item{Fixed a bug whereby STRUC didn't work at all in RDF.} + \item{Fixed a problem with group specification in PUBDEFs in OBJ.} + \item{Improved ease of adding new output formats. Contribution due to Fox Cutter.} + \item{Fixed a bug in relocations in the `bin' format: was showing up when + a relocatable reference crossed an 8192-byte boundary in any output + section.} + \item{Fixed a bug in local labels: local-label lookups were inconsistent + between passes one and two if an EQU occurred between the definition + of a global label and the subsequent use of a local label local to + that global.} + \item{Fixed a seg-fault in the preprocessor (again) which happened when + you use a blank line as the first line of a multi-line macro + definition and then defined a label on the same line as a call to + that macro.} + \item{Fixed a stale-pointer bug in the handling of the NASM environment + variable. Thanks to Thomas McWilliams.} + \item{ELF had a hard limit on the number of sections which caused + segfaults when transgressed. Fixed.} + \item{Added ability for ndisasm to read from stdin by using `-' as the + filename.} + \item{ndisasm wasn't outputting the TO keyword. Fixed.} + \item{Fixed error cascade on bogus expression in \code{\%if} - an error in + evaluation was causing the entire \code{\%if} to be discarded, thus creating + trouble later when the \code{\%else} or \code{\%endif} was encountered.} + \item{Forward reference tracking was instruction-granular not operand- + granular, which was causing 286-specific code to be generated + needlessly on code of the form `shr word [forwardref],1'. Thanks to + Jim Hague for sending a patch.} + \item{All messages now appear on stdout, as sending them to stderr serves + no useful purpose other than to make redirection difficult.} + \item{Fixed the problem with EQUs pointing to an external symbol - this + now generates an error message.} + \item{Allowed multiple size prefixes to an operand, of which only the first + is taken into account.} + \item{Incorporated John Fine's changes, including fixes of a large number + of preprocessor bugs, some small problems in OBJ, and a reworking of + label handling to define labels before their line is assembled, rather + than after.} + \item{Reformatted a lot of the source code to be more readable. Included + 'coding.txt' as a guideline for how to format code for contributors.} + \item{Stopped nested \code{\%reps} causing a panic - they now cause a slightly more + friendly error message instead.} + \item{Fixed floating point constant problems (patch by Pedro Gimeno)} + \item{Fixed the return value of insn\_size() not being checked for -1, indicating + an error.} + \item{Incorporated 3Dnow! instructions.} + \item{Fixed the 'mov eax, eax + ebx' bug.} + \item{Fixed the GLOBAL EQU bug in ELF. Released developers release 3.} + \item{Incorporated John Fine's command line parsing changes} + \item{Incorporated David Lindauer's OMF debug support} + \item{Made changes for LCC 4.0 support (\code{\_\_NASM\_CDecl\_\_}, removed register size + specification warning when sizes agree).} +\end{itemize} + +\xsection{cl-0.9x}{NASM 0.9 Series} + +Revisions before 0.98. + +\xsubsection{cl-0.97}{Version 0.97 released December 1997} + +\begin{itemize} + \item{This was entirely a bug-fix release to 0.96, which seems to have got + cursed. Silly me.} + \item{Fixed stupid mistake in OBJ which caused `MOV EAX,<constant>' to + fail. Caused by an error in the `MOV EAX,<segment>' support.} + \item{ndisasm hung at EOF when compiled with lcc on Linux because lcc on + Linux somehow breaks feof(). ndisasm now does not rely on feof().} + \item{A heading in the documentation was missing due to a markup error in + the indexing. Fixed.} + \item{Fixed failure to update all pointers on realloc() within extended- + operand code in parser.c. Was causing wrong behaviour and seg faults + on lines such as `dd 0.0,0.0,0.0,0.0,...'} + \item{Fixed a subtle preprocessor bug whereby invoking one multi-line + macro on the first line of the expansion of another, when the second + had been invoked with a label defined before it, didn't expand the + inner macro.} + \item{Added internal.doc back in to the distribution archives - it was + missing in 0.96 *blush*} + \item{Fixed bug causing 0.96 to be unable to assemble its own test files, + specifically objtest.asm. *blush again*} + \item{Fixed seg-faults and bogus error messages caused by mismatching + \code{\%rep} and \code{\%endrep} within multi-line macro definitions.} + \item{Fixed a problem with buffer overrun in OBJ, which was causing + corruption at ends of long PUBDEF records.} + \item{Separated DOS archives into main-program and documentation to reduce + download size.} +\end{itemize} + +\xsubsection{cl-0.96}{Version 0.96 released November 1997} + +\begin{itemize} + \item{Fixed a bug whereby, if `nasm sourcefile' would cause a filename + collision warning and put output into `nasm.out', then `nasm + sourcefile -o outputfile' still gave the warning even though the + `-o' was honoured. + Fixed name pollution under Digital UNIX: one of its header files + defined R\_SP, which broke the enum in nasm.h.} + \item{Fixed minor instruction table problems: FUCOM and FUCOMP didn't have + two-operand forms; NDISASM didn't recognise the longer register + forms of PUSH and POP (eg FF F3 for PUSH BX); TEST mem,imm32 was + flagged as undocumented; the 32-bit forms of CMOV had 16-bit operand + size prefixes; `AAD imm' and `AAM imm' are no longer flagged as + undocumented because the Intel Architecture reference documents + them.} + \item{Fixed a problem with the local-label mechanism, whereby strange + types of symbol (EQUs, auto-defined OBJ segment base symbols) + interfered with the `previous global label' value and screwed up + local labels.} + \item{Fixed a bug whereby the stub preprocessor didn't communicate with + the listing file generator, so that the -a and -l options in + conjunction would produce a useless listing file.} + \item{Merged `os2' object file format back into `obj', after discovering + that `obj' \emph{also} shouldn't have a link pass separator in a module + containing a non-trivial MODEND. Flat segments are now declared + using the FLAT attribute. `os2' is no longer a valid object format + name: use `obj'.} + \item{Removed the fixed-size temporary storage in the evaluator. Very very + long expressions (like `mov ax,1+1+1+1+...' for two hundred 1s or + so) should now no longer crash NASM.} + \item{Fixed a bug involving segfaults on disassembly of MMX instructions, + by changing the meaning of one of the operand-type flags in nasm.h. + This may cause other apparently unrelated MMX problems; it needs to + be tested thoroughly.} + \item{Fixed some buffer overrun problems with large OBJ output files. + Thanks to DJ Delorie for the bug report and fix.} + \item{Made preprocess-only mode actually listen to the \code{\%line} markers as it + prints them, so that it can report errors more sanely.} + \item{Re-designed the evaluator to keep more sensible track of expressions + involving forward references: can now cope with previously-nightmare + situations such as: +\begin{lstlisting} +mov ax,foo | bar +foo equ 1 +bar equ 2 +\end{lstlisting}} + \item{Added the ALIGN and ALIGNB standard macros.} + \item{Added PIC support in ELF: use of WRT to obtain the four extra + relocation types needed.} + \item{Added the ability for output file formats to define their own + extensions to the GLOBAL, COMMON and EXTERN directives.} + \item{Implemented common-variable alignment, and global-symbol type and + size declarations, in ELF.} + \item{Implemented NEAR and FAR keywords for common variables, plus + far-common element size specification, in OBJ.} + \item{Added a feature whereby EXTERNs and COMMONs in OBJ can be given a + default WRT specification (either a segment or a group).} + \item{Transformed the Unix NASM archive into an auto-configuring package.} + \item{Added a sanity-check for people applying SEG to things which are + already segment bases: this previously went unnoticed by the SEG + processing and caused OBJ-driver panics later.} + \item{Added the ability, in OBJ format, to deal with `MOV EAX,<segment>' + type references: OBJ doesn't directly support dword-size segment + base fixups, but as long as the low two bytes of the constant term + are zero, a word-size fixup can be generated instead and it will + work.} + \item{Added the ability to specify sections' alignment requirements in + Win32 object files and pure binary files.} + \item{Added preprocess-time expression evaluation: the \code{\%assign} (and + \code{\%iassign}) directive and the bare \code{\%if} (and \code{\%elif}) conditional. + Added relational operators to the evaluator, for use only in \code{\%if} + constructs: the standard relationals = < > <= >= <> (and C-like + synonyms == and !=) plus low-precedence logical operators \&\&, + \textasciicircum \textasciicircum and ||.} + \item{Added a preprocessor repeat construct: \code{\%rep}, \code{\%exitrep}, + \code{\%endrep}.} + \item{Added the \_\_FILE\_\_ and \_\_LINE\_\_ standard macros.} + \item{Added a sanity check for number constants being greater than + 0xFFFFFFFF. The warning can be disabled.} + \item{Added the \%0 token whereby a variadic multi-line macro can tell how + many parameters it's been given in a specific invocation.} + \item{Added \code{\%rotate}, allowing multi-line macro parameters to be cycled.} + \item{Added the `*' option for the maximum parameter count on multi-line + macros, allowing them to take arbitrarily many parameters.} + \item{Added the ability for the user-level forms of EXTERN, GLOBAL and + COMMON to take more than one argument.} + \item{Added the IMPORT and EXPORT directives in OBJ format, to deal with + Windows DLLs.} + \item{Added some more preprocessor \code{\%if} constructs: \code{\%ifidn}, + \code{\%ifidni} (exact textual identity), and \code{\%ifid}, + \code{\%ifnum}, \code{\%ifstr} (token type testing).} + \item{Added the ability to distinguish SHL AX,1 (the 8086 version) from + SHL AX,BYTE 1 (the 286-and-upwards version whose constant happens to + be 1).} + \item{Added NetBSD/FreeBSD/OpenBSD's variant of a.out format, complete + with PIC shared library features.} + \item{Changed NASM's idiosyncratic handling of FCLEX, FDISI, FENI, FINIT, + FSAVE, FSTCW, FSTENV, and FSTSW to bring it into line with the + otherwise accepted standard. The previous behaviour, though it was a + deliberate feature, was a deliberate feature based on a + misunderstanding. Apologies for the inconvenience.} + \item{Improved the flexibility of ABSOLUTE: you can now give it an + expression rather than being restricted to a constant, and it can + take relocatable arguments as well.} + \item{Added the ability for a variable to be declared as EXTERN multiple + times, and the subsequent definitions are just ignored.} + \item{We now allow instruction prefixes (CS, DS, LOCK, REPZ etc) to be + alone on a line (without a following instruction).} + \item{Improved sanity checks on whether the arguments to EXTERN, GLOBAL + and COMMON are valid identifiers.} + \item{Added misc/exebin.mac to allow direct generation of .EXE files by + hacking up an EXE header using DB and DW; also added test/binexe.asm + to demonstrate the use of this. Thanks to Yann Guidon for + contributing the EXE header code.} + \item{ndisasm forgot to check whether the input file had been successfully + opened. Now it does. Doh!} + \item{Added the Cyrix extensions to the MMX instruction set.} + \item{Added a hinting mechanism to allow [EAX+EBX] and [EBX+EAX] to be + assembled differently. This is important since [ESI+EBP] and + [EBP+ESI] have different default base segment registers.} + \item{Added support for the PharLap OMF extension for 4096-byte segment + alignment.} +\end{itemize} + +\xsubsection{cl-0.95}{Version 0.95 released July 1997} + +\begin{itemize} + \item{Fixed yet another ELF bug. This one manifested if the user relied on + the default segment, and attempted to define global symbols without + first explicitly declaring the target segment.} + \item{Added makefiles (for NASM and the RDF tools) to build Win32 console + apps under Symantec C++. Donated by Mark Junker.} + \item{Added `macros.bas' and `insns.bas', QBasic versions of the Perl + scripts that convert `standard.mac' to `macros.c' and convert + `insns.dat' to `insnsa.c' and `insnsd.c'. Also thanks to Mark + Junker.} + \item{Changed the diassembled forms of the conditional instructions so + that JB is now emitted as JC, and other similar changes. Suggested + list by Ulrich Doewich.} + \item{Added `@' to the list of valid characters to begin an identifier with.} + \item{Documentary changes, notably the addition of the `Common Problems' + section in nasm.doc.} + \item{Fixed a bug relating to 32-bit PC-relative fixups in OBJ.} + \item{Fixed a bug in perm\_copy() in labels.c which was causing exceptions + in cleanup\_labels() on some systems.} + \item{Positivity sanity check in TIMES argument changed from a warning to + an error following a further complaint.} + \item{Changed the acceptable limits on byte and word operands to allow + things like `\textasciitilde 10111001b' to work.} + \item{Fixed a major problem in the preprocessor which caused seg-faults if + macro definitions contained blank lines or comment-only lines.} + \item{Fixed inadequate error checking on the commas separating the + arguments to `db', `dw' etc.} + \item{Fixed a crippling bug in the handling of macros with operand counts + defined with a `+' modifier.} + \item{Fixed a bug whereby object file formats which stored the input file + name in the output file (such as OBJ and COFF) weren't doing so + correctly when the output file name was specified on the command + line.} + \item{Removed [INC] and [INCLUDE] support for good, since they were + obsolete anyway.} + \item{Fixed a bug in OBJ which caused all fixups to be output in 16-bit + (old-format) FIXUPP records, rather than putting the 32-bit ones in + FIXUPP32 (new-format) records.} + \item{Added, tentatively, OS/2 object file support (as a minor variant + on OBJ).} + \item{Updates to Fox Cutter's Borland C makefile, Makefile.bc2.} + \item{Removed a spurious second fclose() on the output file.} + \item{Added the `-s' command line option to redirect all messages which + would go to stderr (errors, help text) to stdout instead.} + \item{Added the `-w' command line option to selectively suppress some + classes of assembly warning messages.} + \item{Added the `-p' pre-include and `-d' pre-define command-line options.} + \item{Added an include file search path: the `-i' command line option.} + \item{Fixed a silly little preprocessor bug whereby starting a line with a + `\%!' environment-variable reference caused an `unknown directive' + error.} + \item{Added the long-awaited listing file support: the `-l' command line + option.} + \item{Fixed a problem with OBJ format whereby, in the absence of any + explicit segment definition, non-global symbols declared in the + implicit default segment generated spurious EXTDEF records in the + output.} + \item{Added the NASM environment variable.} + \item{From this version forward, Win32 console-mode binaries will be + included in the DOS distribution in addition to the 16-bit binaries. + Added Makefile.vc for this purpose.} + \item{Added `return 0;' to test/objlink.c to prevent compiler warnings.} + \item{Added the \_\_NASM\_MAJOR\_\_ and \_\_NASM\_MINOR\_\_ standard defines.} + \item{Added an alternative memory-reference syntax in which prefixing an + operand with `\&' is equivalent to enclosing it in square brackets, + at the request of Fox Cutter.} + \item{Errors in pass two now cause the program to return a non-zero error + code, which they didn't before.} + \item{Fixed the single-line macro cycle detection, which didn't work at + all on macros with no parameters (caused an infinite loop). Also + changed the behaviour of single-line macro cycle detection to work + like cpp, so that macros like `extrn' as given in the documentation + can be implemented.} + \item{Fixed the implementation of WRT, which was too restrictive in that + you couldn't do `mov ax,[di+abc wrt dgroup]' because (di+abc) wasn't + a relocatable reference.} +\end{itemize} + +\xsubsection{cl-0.94}{Version 0.94 released April 1997} + +\begin{itemize} + \item{Major item: added the macro processor.} + \item{Added undocumented instructions SMI, IBTS, XBTS and LOADALL286. Also + reorganised CMPXCHG instruction into early-486 and Pentium forms. + Thanks to Thobias Jones for the information.} + \item{Fixed two more stupid bugs in ELF, which were causing `ld' to + continue to seg-fault in a lot of non-trivial cases.} + \item{Fixed a seg-fault in the label manager.} + \item{Stopped FBLD and FBSTP from \emph{requiring} the TWORD keyword, which is + the only option for BCD loads/stores in any case.} + \item{Ensured FLDCW, FSTCW and FSTSW can cope with the WORD keyword, if + anyone bothers to provide it. Previously they complained unless no + keyword at all was present.} + \item{Some forms of FDIV/FDIVR and FSUB/FSUBR were still inverted: a + vestige of a bug that I thought had been fixed in 0.92. This was + fixed, hopefully for good this time...} + \item{Another minor phase error (insofar as a phase error can \emph{ever} be + minor) fixed, this one occurring in code of the form +\begin{lstlisting} +rol ax,forward_reference +forward_reference equ 1 +\end{lstlisting}} + \item{The number supplied to TIMES is now sanity-checked for positivity, + and also may be greater than 64K (which previously didn't work on + 16-bit systems).} + \item{Added Watcom C makefiles, and misc/pmw.bat, donated by Dominik Behr.} + \item{Added the INCBIN pseudo-opcode.} + \item{Due to the advent of the preprocessor, the [INCLUDE] and [INC] + directives have become obsolete. They are still supported in this + version, with a warning, but won't be in the next.} + \item{Fixed a bug in OBJ format, which caused incorrect object records to + be output when absolute labels were made global.} + \item{Updates to RDOFF subdirectory, and changes to outrdf.c.} +\end{itemize} + +\xsubsection{cl-0.93}{Version 0.93 released January 1997} + +This release went out in a great hurry after semi-crippling bugs +were found in 0.92. + +\begin{itemize} + \item{Really \emph{did} fix the stack overflows this time. *blush*} + \item{Had problems with EA instruction sizes changing between passes, when + an offset contained a forward reference and so 4 bytes were + allocated for the offset in pass one; by pass two the symbol had + been defined and happened to be a small absolute value, so only 1 + byte got allocated, causing instruction size mismatch between passes + and hence incorrect address calculations. Fixed.} + \item{Stupid bug in the revised ELF section generation fixed (associated + string-table section for .symtab was hard-coded as 7, even when this + didn't fit with the real section table). Was causing `ld' to + seg-fault under Linux.} + \item{Included a new Borland C makefile, Makefile.bc2, donated by Fox + Cutter <lmb@comtch.iea.com>.} +\end{itemize} + +\xsubsection{cl-0.92}{Version 0.92 released January 1997} + +\begin{itemize} + \item{The FDIVP/FDIVRP and FSUBP/FSUBRP pairs had been inverted: this was + fixed. This also affected the LCC driver.} + \item{Fixed a bug regarding 32-bit effective addresses of the form + \code{[other\_register+ESP]}.} + \item{Documentary changes, notably documentation of the fact that Borland + Win32 compilers use `obj' rather than `win32' object format.} + \item{Fixed the COMENT record in OBJ files, which was formatted + incorrectly.} + \item{Fixed a bug causing segfaults in large RDF files.} + \item{OBJ format now strips initial periods from segment and group + definitions, in order to avoid complications with the local label + syntax.} + \item{Fixed a bug in disassembling far calls and jumps in NDISASM.} + \item{Added support for user-defined sections in COFF and ELF files.} + \item{Compiled the DOS binaries with a sensible amount of stack, to + prevent stack overflows on any arithmetic expression containing + parentheses.} + \item{Fixed a bug in handling of files that do not terminate in a newline.} +\end{itemize} + +\xsubsection{cl-0.91}{Version 0.91 released November 1996} + +\begin{itemize} + \item{Loads of bug fixes.} + \item{Support for RDF added.} + \item{Support for DBG debugging format added.} + \item{Support for 32-bit extensions to Microsoft OBJ format added.} + \item{Revised for Borland C: some variable names changed, makefile added.} + \item{LCC support revised to actually work.} + \item{JMP/CALL NEAR/FAR notation added.} + \item{`a16', `o16', `a32' and `o32' prefixes added.} + \item{Range checking on short jumps implemented.} + \item{MMX instruction support added.} + \item{Negative floating point constant support added.} + \item{Memory handling improved to bypass 64K barrier under DOS.} + \item{\code{\$} prefix to force treatment of reserved words as identifiers added.} + \item{Default-size mechanism for object formats added.} + \item{Compile-time configurability added.} + \item{\code{\#}, \code{\@}, \code{\textasciitilde} and \code{?} are now valid characters in labels.} + \item{\code{-e} and \code{-k} options in NDISASM added.} +\end{itemize} + +\xsubsection{cl-0.90} Version 0.90 released October 1996 + +First release version. First support for object file output. Other +changes from previous version (0.3x) too numerous to document. diff --git a/doc/latex/src/contact.tex b/doc/latex/src/contact.tex new file mode 100644 index 00000000..f90631af --- /dev/null +++ b/doc/latex/src/contact.tex @@ -0,0 +1,111 @@ +% +% vim: ts=4 sw=4 et +% +\xchapter{contact}{Contact Information} + +\xsection{website}{Website} + +NASM has a \textindex{website} at \href{http://www.nasm.us/}{http://www.nasm.us/}. + +\textindexlc{New releases}, \textindex{release candidates}, and +\index{snapshots!daily development}\textindex{daily development snapshots} +of NASM are available from the official web site in source form as well +as binaries for a number of common platforms. + +\xsubsection{forums}{User Forums} + +Users of NASM may find the Forums on the website useful. These are, +however, not frequented much by the developers of NASM, so they are +not suitable for reporting bugs. + +\xsubsection{develcom}{Development Community} + +The development of NASM is coordinated primarily though the +\codeindex{nasm-devel} mailing list. If you wish to participate in +development of NASM, please join this mailing list. Subscription +links and archives of past posts are available on the website. + +\xsection{bugs}{Reporting Bugs} +\index{bugs} + +To report bugs in NASM, please use the \textindex{bug tracker} at +\href{http://www.nasm.us/}{http://www.nasm.us/} (click on "Bug Tracker"), +or if that fails then through one of the contacts in \nref{website}. + +Please read \nref{qstart} first, and don't report the bug if it's +listed in there as a deliberate feature. (If you think the feature +is badly thought out, feel free to send us reasons why you think it +should be changed, but don't just send us mail saying `This is a +bug' if the documentation says we did it on purpose.) Then read +\nref{problems}, and don't bother reporting the bug if it's +listed there. + +If you do report a bug, \emph{please} make sure your bug report includes +the following information: + +\begin{itemize} + \item{What operating system you're running NASM under. Linux, + FreeBSD, NetBSD, MacOS X, Win16, Win32, Win64, MS-DOS, OS/2, VMS, + whatever.} + + \item{If you compiled your own executable from a source archive, compiled + your own executable from \code{git}, used the standard distribution + binaries from the website, or got an executable from somewhere else + (e.g. a Linux distribution.) If you were using a locally built + executable, try to reproduce the problem using one of the standard + binaries, as this will make it easier for us to reproduce your problem + prior to fixing it.} + + \item{Which version of NASM you're using, and exactly how you invoked + it. Give us the precise command line, and the contents of the + \code{NASMENV} environment variable if any.} + + \item{Which versions of any supplementary programs you're using, and + how you invoked them. If the problem only becomes visible at link + time, tell us what linker you're using, what version of it you've + got, and the exact linker command line. If the problem involves + linking against object files generated by a compiler, tell us what + compiler, what version, and what command line or options you used. + (If you're compiling in an IDE, please try to reproduce the problem + with the command-line version of the compiler.)} + + \item{If at all possible, send us a NASM source file which exhibits the + problem. If this causes copyright problems (e.g. you can only + reproduce the bug in restricted-distribution code) then bear in mind + the following two points: firstly, we guarantee that any source code + sent to us for the purposes of debugging NASM will be used \emph{only} + for the purposes of debugging NASM, and that we will delete all our + copies of it as soon as we have found and fixed the bug or bugs in + question; and secondly, we would prefer \emph{not} to be mailed large + chunks of code anyway. The smaller the file, the better. A + three-line sample file that does nothing useful \emph{except} + demonstrate the problem is much easier to work with than a + fully fledged ten-thousand-line program. (Of course, some errors + \emph{do} only crop up in large files, so this may not be possible.)} + + \item{A description of what the problem actually \emph{is}. `It doesn't + work' is \emph{not} a helpful description! Please describe exactly what + is happening that shouldn't be, or what isn't happening that should. + Examples might be: `NASM generates an error message saying Line 3 + for an error that's actually on Line 5'; `NASM generates an error + message that I believe it shouldn't be generating at all'; `NASM + fails to generate an error message that I believe it \emph{should} be + generating'; `the object file produced from this source code crashes + my linker'; `the ninth byte of the output file is 66 and I think it + should be 77 instead'.} + + \item{If you believe the output file from NASM to be faulty, send it to + us. That allows us to determine whether our own copy of NASM + generates the same file, or whether the problem is related to + portability issues between our development platforms and yours. We + can handle binary files mailed to us as MIME attachments, uuencoded, + and even BinHex. Alternatively, we may be able to provide an FTP + site you can upload the suspect files to; but mailing them is easier + for us.} + + \item{Any other information or data files that might be helpful. If, + for example, the problem involves NASM failing to generate an object + file while TASM can generate an equivalent file without trouble, + then send us \emph{both} object files, so we can see what TASM is doing + differently from us.} +\end{itemize} diff --git a/doc/latex/src/directive.tex b/doc/latex/src/directive.tex new file mode 100644 index 00000000..964315cd --- /dev/null +++ b/doc/latex/src/directive.tex @@ -0,0 +1,541 @@ +% +% vim: ts=4 sw=4 et +% +\xchapter{directive}{\textindexlc{Assembler Directives}} + +NASM, though it attempts to avoid the bureaucracy of assemblers like +MASM and TASM, is nevertheless forced to support a \emph{few} +directives. These are described in this chapter. + +NASM's directives come in two types: \index{directives!user-level} +\emph{user-level} directives and \index{directives!primitive} +\emph{primitive} directives. Typically, each directive has a +user-level form and a primitive form. In almost all cases, we +recommend that users use the user-level forms of the directives, +which are implemented as macros which call the primitive forms. + +Primitive directives are enclosed in square brackets; user-level +directives are not. + +In addition to the universal directives described in this chapter, +each object file format can optionally supply extra directives in +order to control particular features of that file format. These +\index{directives!format-specific}\emph{format-specific} directives are +documented along with the formats that implement them, in +\nref{outfmt}. + +\xsection{bits}{\codeindex{BITS}: Specifying Target \textindexlc{Processor Mode}} + +The \code{BITS} directive specifies whether NASM should generate code +\index{16-bit mode, versus 32-bit mode}designed to run on a processor +operating in 16-bit mode, 32-bit mode or 64-bit mode. The syntax is +\code{BITS XX}, where XX is 16, 32 or 64. + +In most cases, you should not need to use \code{BITS} explicitly. The +\code{aout}, \code{coff}, \code{elf32}, \code{elf64}, \code{macho32}, +\code{macho64}, \code{win32} and \code{win64} object formats, which +are designed for use in 32-bit or 64-bit operating systems, all cause +NASM to select 32-bit or 64-bit mode, respectively, by default. +The \code{obj} object format allows you to specify each segment +you define as either \code{USE16} or \code{USE32}, and NASM will +set its operating mode accordingly, so the use of the \code{BITS} +directive is once again unnecessary. + +The most likely reason for using the \code{BITS} directive is to write +32-bit or 64-bit code in a flat binary file; this is because the \code{bin} +output format defaults to 16-bit mode in anticipation of it being +used most frequently to write DOS \code{.COM} programs, DOS \code{.SYS} +device drivers and boot loader software. + +The \code{BITS} directive can also be used to generate code for +a different mode than the standard one for the output format. + +You do \emph{not} need to specify \code{BITS 32} merely in order +to use 32-bit instructions in a 16-bit DOS program; if you do, the +assembler will generate incorrect code because it will be writing +code targeted at a 32-bit platform, to be run on a 16-bit one. + +When NASM is in \code{BITS 16} mode, instructions which use 32-bit +data are prefixed with an 0x66 byte, and those referring to 32-bit +addresses have an 0x67 prefix. In \code{BITS 32} mode, the reverse is +true: 32-bit instructions require no prefixes, whereas instructions +using 16-bit data need an 0x66 and those working on 16-bit +addresses need an 0x67. + +When NASM is in \code{BITS 64} mode, most instructions operate the same +as they do for \code{BITS 32} mode. However, there are 8 more general and +SSE registers, and 16-bit addressing is no longer supported. + +The default address size is 64 bits; 32-bit addressing can be selected +with the 0x67 prefix. The default operand size is still 32 bits, +however, and the 0x66 prefix selects 16-bit operand size. +The \code{REX} prefix is used both to select 64-bit operand size, and +to access the new registers. NASM automatically inserts REX prefixes +when necessary. + +When the \code{REX} prefix is used, the processor does not know how to +address the AH, BH, CH or DH (high 8-bit legacy) registers. Instead, +it is possible to access the the low 8-bits of the SP, BP SI and DI +registers as SPL, BPL, SIL and DIL, respectively; but only when the +REX prefix is used. + +The \code{BITS} directive has an exactly equivalent primitive form, +\code{[BITS 16]}, \code{[BITS 32]} and \code{[BITS 64]}. The user-level +form is a macro which has no function other than to call the primitive form. + +Note that the space is neccessary, e.g. \code{BITS32} will \emph{not} work! + +\xsubsection{use163264}{\codeindex{USE16}, \codeindex{USE32} +and \codeindex{USE64}: Aliases for BITS} + +The \code{USE16}, \code{USE32} and \code{USE64} directives can be used +in place of \code{BITS 16}, \code{BITS 32} and \code{BITS 64}, for +compatibility with other assemblers. + +\xsection{default}{\codeindex{DEFAULT}: Change the assembler defaults} + +The \code{DEFAULT} directive changes the assembler defaults. Normally, +NASM defaults to a mode where the programmer is expected to explicitly +specify most features directly. However, this is occasionally obnoxious, +as the explicit form is pretty much the only one one wishes to use. + +Currently, \code{DEFAULT} can be set to \code{REL}, \code{ABS}, \code{BND} +and \code{NOBND}. + +\xsubsection{relabs}{\codeindex{REL} and \codeindex{ABS}: RIP-relative addressing} + +This sets whether registerless instructions in 64-bit mode are +\code{RIP}-relative or not. By default, they are absolute unless +overridden with the \codeindex{REL} specifier (see \nref{effaddr}). +However, if \code{DEFAULT REL} is specified, \code{REL} is default, unless +overridden with the \code{ABS} specifier, \emph{except when used with an +FS or GS segment override}. + +The special handling of \code{FS} and \code{GS} overrides are due to the +fact that these registers are generally used as thread pointers or +other special functions in 64-bit mode, and generating +\code{RIP}-relative addresses would be extremely confusing. + +\code{DEFAULT REL} is disabled with \code{DEFAULT ABS}. + +\xsubsection{bndnobnd}{\codeindex{BND} and \codeindex{NOBND}: \code{BND} prefix} + +If \code{DEFAULT BND} is set, all bnd-prefix available instructions +following this directive are prefixed with bnd. To override it, +\code{NOBND} prefix can be used. + +\begin{lstlisting} +DEFAULT BND + call foo ; BND will be prefixed + nobnd call foo ; BND will NOT be prefixed +\end{lstlisting} + +\code{DEFAULT NOBND} can disable \code{DEFAULT BND} and then +\code{BND} prefix will be added only when explicitly specified +in code. + +\code{DEFAULT BND} is expected to be the normal configuration +for writing MPX-enabled code. + +\xsection{section}{\codeindex{SECTION} or \codeindex{SEGMENT}: Changing and +\textindexlc{Defining Sections}} + +\index{sections!changing}\index{sections!switching between} +The \code{SECTION} directive (\code{SEGMENT} is an exactly equivalent +synonym) changes which section of the output file the code you write +will be assembled into. In some object file formats, the number and +names of sections are fixed; in others, the user may make up as many +as they wish. Hence \code{SECTION} may sometimes give an error message, +or may define a new section, if you try to switch to a section that does +not (yet) exist. + +The Unix object formats, and the \code{bin} object format (but see +\nref{multisec}), all support the \index{sections!standardized names} +standardized names \code{.text}, \code{.data} and \code{.bss} for the code, +data and uninitialized-data sections. The \code{obj} format, by contrast, +does not recognize these section names as being special, and indeed will +strip off the leading period of any section name that has one. + +\xsubsection{sectmac}{The \codeindex{\_\_SECT\_\_} Macro} + +The \code{SECTION} directive is unusual in that its user-level form +functions differently from its primitive form. The primitive form, +\code{[SECTION xyz]}, simply switches the current target section to the +one given. The user-level form, \code{SECTION xyz}, however, first +defines the single-line macro \code{\_\_SECT\_\_} to be the primitive +\code{[SECTION]} directive which it is about to issue, and then issues +it. So the user-level directive + +\begin{lstlisting} + SECTION .text +\end{lstlisting} + +expands to the two lines + +\begin{lstlisting} +%define __SECT__ [SECTION .text] + [SECTION .text] +\end{lstlisting} + +Users may find it useful to make use of this in their own macros. +For example, the \code{writefile} macro defined in \nref{mlmacgre} +can be usefully rewritten in the following more sophisticated form: + +\begin{lstlisting} +%macro writefile 2+ + [section .data] + + %%str: db %2 + %%endstr: + + __SECT__ + + mov dx, %%str + mov cx, %%endstr-%%str + mov bx, %1 + mov ah, 0x40 + int 0x21 +%endmacro +\end{lstlisting} + +This form of the macro, once passed a string to output, first +switches temporarily to the data section of the file, using the +primitive form of the \code{SECTION} directive so as not to modify +\code{\_\_SECT\_\_}. It then declares its string in the data section, +and then invokes \code{\_\_SECT\_\_} to switch back to \emph{whichever} +section the user was previously working in. It thus avoids the need, +in the previous version of the macro, to include a \code{JMP} instruction +to jump over the data, and also does not fail if, in a complicated +\code{OBJ} format module, the user could potentially be assembling the +code in any of several separate code sections. + +\xsection{absolute}{\codeindex{ABSOLUTE}: Defining Absolute Labels} + +The \code{ABSOLUTE} directive can be thought of as an alternative form +of \code{SECTION}: it causes the subsequent code to be directed at no +physical section, but at the hypothetical section starting at the +given absolute address. The only instructions you can use in this +mode are the \code{RESB} family. + +\code{ABSOLUTE} is used as follows: + +\begin{lstlisting} +absolute 0x1A + + kbuf_chr resw 1 + kbuf_free resw 1 + kbuf resw 16 +\end{lstlisting} + +This example describes a section of the PC BIOS data area, at +segment address 0x40: the above code defines \code{kbuf\_chr} to be +0x1A, \code{kbuf\_free} to be 0x1C, and \code{kbuf} to be 0x1E. + +The user-level form of \code{ABSOLUTE}, like that of \code{SECTION}, +redefines the \codeindex{\_\_SECT\_\_} macro when it is invoked. + +\codeindex{STRUC} and \codeindex{ENDSTRUC} are defined as macros +which use \code{ABSOLUTE} (and also \code{\_\_SECT\_\_}). + +\code{ABSOLUTE} doesn't have to take an absolute constant as an +argument: it can take an expression (actually, a \textindex{critical +expression}: see \nref{crit}) and it can be a value in a segment. +For example, a TSR can re-use its setup code as run-time BSS like this: + +\begin{lstlisting} + org 100h ; it's a .COM program + jmp setup ; setup code comes last + ; the resident part of the TSR goes here + ; ... +setup: + ; now write the code that installs the TSR here + ; ... +absolute setup + +runtimevar1 resw 1 +runtimevar2 resd 20 + +tsr_end: +\end{lstlisting} + +This defines some variables ``on top of'' the setup code, so that +after the setup has finished running, the space it took up can be +re-used as data storage for the running TSR. The symbol +\code{tsr\_end} can be used to calculate the total size of +the part of the TSR that needs to be made resident. + +\xsection{extern}{\codeindex{EXTERN}: \textindexlc{Importing Symbols} from Other Modules} + +\code{EXTERN} is similar to the MASM directive \code{EXTRN} and +the C keyword \code{extern}: it is used to declare a symbol which +is not defined anywhere in the module being assembled, but is assumed +to be defined in some other module and needs to be referred to by this +one. Not every object-file format can support external variables: +the \code{bin} format cannot. + +The \code{EXTERN} directive takes as many arguments as you like. +Each argument is the name of a symbol: + +\begin{lstlisting} +extern _printf +extern _sscanf,_fscanf +\end{lstlisting} + +Some object-file formats provide extra features to the \code{EXTERN} +directive. In all cases, the extra features are used by suffixing a +colon to the symbol name followed by object-format specific text. +For example, the \code{obj} format allows you to declare that the +default segment base of an external should be the group \code{dgroup} +by means of the directive + +\begin{lstlisting} +extern _variable:wrt dgroup +\end{lstlisting} + +The primitive form of \code{EXTERN} differs from the user-level form +only in that it can take only one argument at a time: the support +for multiple arguments is implemented at the preprocessor level. + +You can declare the same variable as \code{EXTERN} more than once: NASM +will quietly ignore the second and later redeclarations. + +If a variable is declared both \code{GLOBAL} and \code{EXTERN}, or +if it is declared as \code{EXTERN} and then defined, it will be +treated as \code{GLOBAL}. If a variable is declared both as +\code{COMMON} and \code{EXTERN}, it will be treated as \code{COMMON}. + +\xsection{global}{\codeindex{GLOBAL}: \textindexlc{Exporting Symbols} to Other Modules} + +\code{GLOBAL} is the other end of \code{EXTERN}: if one module declares a +symbol as \code{EXTERN} and refers to it, then in order to prevent +linker errors, some other module must actually \emph{define} the +symbol and declare it as \code{GLOBAL}. Some assemblers use the name +\codeindex{PUBLIC} for this purpose. + +\code{GLOBAL} uses the same syntax as \code{EXTERN}, except that it must +refer to symbols which \emph{are} defined in the same module as the +\code{GLOBAL} directive. For example: + +\begin{lstlisting} +global _main +_main: + ; some code +\end{lstlisting} + +\code{GLOBAL}, like \code{EXTERN}, allows object formats to define private +extensions by means of a colon. The \code{elf} object format, for +example, lets you specify whether global data items are functions or +data: + +\begin{lstlisting} +global hashlookup:function, hashtable:data +\end{lstlisting} + +Like \code{EXTERN}, the primitive form of \code{GLOBAL} differs +from the user-level form only in that it can take only one argument +at a time. + +\xsection{common}{\codeindex{COMMON}: Defining Common Data Areas} + +The \code{COMMON} directive is used to declare \textindex{\emph{common +variables}}. A common variable is much like a global variable declared +in the uninitialized data section, so that + +\begin{lstlisting} +common intvar 4 +\end{lstlisting} + +is similar in function to + +\begin{lstlisting} +global intvar +section .bss + +intvar resd 1 +\end{lstlisting} + +The difference is that if more than one module defines the same +common variable, then at link time those variables will be +\emph{merged}, and references to \code{intvar} in all modules +will point at the same piece of memory. + +Like \code{GLOBAL} and \code{EXTERN}, \code{COMMON} supports +object-format specific extensions. For example, the \code{obj} +format allows common variables to be NEAR or FAR, and the \code{elf} +format allows you to specify the alignment requirements of +a common variable: + +\begin{lstlisting} +common commvar 4:near ; works in OBJ +common intarray 100:4 ; works in ELF: 4 byte aligned +\end{lstlisting} + +Once again, like \code{EXTERN} and \code{GLOBAL}, the primitive form of +\code{COMMON} differs from the user-level form only in that it can take +only one argument at a time. + +\xsection{static}{\codeindex{STATIC}: Local Symbols within Modules} + +Opposite to \code{EXTERN} and \code{GLOBAL}, \code{STATIC} is local +symbol, but should be named according to the global mangling rules +(named by analogy with the C keyword \code{static} as applied to +functions or global variables). + +\begin{lstlisting} +static foo +foo: + ; codes +\end{lstlisting} + +Unlike \code{GLOBAL}, \code{STATIC} does not allow object formats +to accept private extensions mentioned in \nref{global}. + +\xsection{mangling}{\codeindex{(G|L)PREFIX}, \codeindex{(G|L)POSTFIX}: +Mangling Symbols} + +\code{PREFIX}, \code{GPREFIX}, \code{LPREFIX}, \code{POSTFIX}, +\code{GPOSTFIX}, and \code{LPOSTFIX} directives can prepend or +append the given argument to a certain type of symbols. The directive +should be as a preprocess statement. Each usage is: + +\begin{itemize} + \item{\code{PREFIX}|\code{GPREFIX}: Prepend the argument to all + \code{EXTERN} \code{COMMON}, \code{STATIC}, and + \code{GLOBAL} symbols} + + \item{\code{LPREFIX}: Prepend the argument to all other symbols + such as Local Labels, and backend defined symbols} + + \item{\code{POSTFIX}|\code{GPOSTFIX}: Append the argument to + all \code{EXTERN} \code{COMMON}, \code{STATIC}, and + \code{GLOBAL} symbols} + + \item{\code{LPOSTFIX}: Append the argument to all other symbols + such as Local Labels, and backend defined symbols} +\end{itemize} + +This is a macro implemented as a \code{\%pragma}: + +\begin{lstlisting} +%pragma macho lprefix L_ +\end{lstlisting} + +Commandline option is also possible. See also \nref{opt-pfix}. + +Some toolchains is aware of a particular prefix for its own optimization +options, such as code elimination. For instance, Mach-O backend has a +linker that uses a simplistic naming scheme to chunk up sections into a +meta section. When the \code{subsections\_via\_symbols} directive +(\nref{macho-ssvs}) is declared, each symbol is the start of a +separate block. The meta section is, then, defined to include sections +before the one that starts with a 'L'. \code{LPREFIX} is useful here to +mark all local symbols with the 'L' prefix to be excluded to the meta +section. It converts local symbols compatible with the particular +toolchain. Note that local symbols declared with \code{STATIC} +(\nref{static}) are excluded from the symbol mangling and also +not marked as global. + +\xsection{gen-namespace}{\codeindex{OUTPUT}, \codeindex{DEBUG}: +Generic Namespaces} + +\code{OUTPUT} and \code{DEBUG} are generic \code{\%pragma} namespaces +that are supposed to redirect to the current output and debug formats. +For example, when mangling local symbols via the generic namespace: + +\begin{lstlisting} +%pragma output gprefix _ +\end{lstlisting} + +This is useful when the directive is needed to be output format +agnostic. + +The example is also euquivalent to this, when the output format is +\code{elf}: + +\begin{lstlisting} +%pragma elf gprefix _ +\end{lstlisting} + + +\xsection{cpu}{\codeindex{CPU}: Defining CPU Dependencies} + +The \code{CPU} directive restricts assembly to those instructions which +are available on the specified CPU. + +Options are: + +\begin{tabular}{ l l } + \code{CPU 8086} & Assemble only 8086 instruction set \\ + \code{CPU 186} & Assemble instructions up to the 80186 instruction set \\ + \code{CPU 286} & Assemble instructions up to the 286 instruction set \\ + \code{CPU 386} & Assemble instructions up to the 386 instruction set \\ + \code{CPU 486} & 486 instruction set \\ + \code{CPU 586} & Pentium instruction set \\ + \code{CPU PENTIUM} & Same as 586 \\ + \code{CPU 686} & P6 instruction set \\ + \code{CPU PPRO} & Same as 686 \\ + \code{CPU P2} & Same as 686 \\ + \code{CPU P3} & Pentium III (Katmai) instruction sets \\ + \code{CPU KATMAI} & Same as P3 \\ + \code{CPU P4} & Pentium 4 (Willamette) instruction set \\ + \code{CPU WILLAMETTE} & Same as P4 \\ + \code{CPU PRESCOTT} & Prescott instruction set \\ + \code{CPU X64} & x86-64 (x64/AMD64/Intel 64) instruction set \\ + \code{CPU IA64} & IA64 CPU (in x86 mode) instruction set \\ +\end{tabular} + +All options are case insensitive. All instructions will be selected +only if they apply to the selected CPU or lower. By default, all +instructions are available. + +\xsection{float}{\codeindex{FLOAT}: Handling of \index{constants!floating-point} +floating-point constants} + +By default, floating-point constants are rounded to nearest, and IEEE +denormals are supported. The following options can be set to alter +this behaviour: + +\begin{tabular}{ l l } + \code{FLOAT DAZ} & Flush denormals to zero \\ + \code{FLOAT NODAZ} & Do not flush denormals to zero (default) \\ + \code{FLOAT NEAR} & Round to nearest (default) \\ + \code{FLOAT UP} & Round up (toward +Infinity) \\ + \code{FLOAT DOWN} & Round down (toward -Infinity) \\ + \code{FLOAT ZERO} & Round toward zero \\ + \code{FLOAT DEFAULT} & Restore default settings \\ +\end{tabular} + +The standard macros \codeindex{\_\_FLOAT\_DAZ\_\_}, +\codeindex{\_\_FLOAT\_ROUND\_\_}, and \codeindex{\_\_FLOAT\_\_} contain +the current state, as long as the programmer has avoided the use +of the brackeded primitive form, (\code{[FLOAT]}). + +\code{\_\_FLOAT\_\_} contains the full set of floating-point settings; +this value can be saved away and invoked later to restore the setting. + +\xsection{asmdir-warning}{\codeindex{[WARNING]}: Enable or disable warnings} + +The \code{[WARNING]} directive can be used to enable or disable classes +of warnings in the same way as the \code{-w} option, see \nref{opt-w} +for more details about warning classes. + +\begin{itemize} + \item{\code{[warning +\emph{warning-class}]} enables warnings for + \emph{warning-class}}. + + \item{\code{[warning -\emph{warning-class}]} disables warnings for + \emph{warning-class}}. + + \item{\code{[warning *\emph{warning-class}]} restores \emph{warning-class} to + the original value, either the default value or as specified on the + command line.} + + \item{\code{[warning push]} saves the current warning state on a stack.} + + \item{\code{[warning pop]} restores the current warning state from the stack.} +\end{itemize} + +The \code{[WARNING]} directive also accepts the \code{all}, \code{error} and +\code{error=}\emph{warning-class} specifiers. + +No ``user form'' (without the brackets) currently exists. diff --git a/doc/latex/src/idxconf.ist b/doc/latex/src/idxconf.ist new file mode 100644 index 00000000..cb36fe99 --- /dev/null +++ b/doc/latex/src/idxconf.ist @@ -0,0 +1,9 @@ +% +% vim: ts=4 sw=4 et +% +headings_flag 1 +heading_prefix "\\textcolor{hcolor}{\\textbf{" +heading_suffix "}}\\nopagebreak\n" +delim_0 " \\dotfill " +delim_1 " \\dotfill " +delim_2 " \\dotfill " diff --git a/doc/latex/src/inslist.tex b/doc/latex/src/inslist.tex new file mode 100644 index 00000000..fdd75da8 --- /dev/null +++ b/doc/latex/src/inslist.tex @@ -0,0 +1,14 @@ +% +% vim: ts=4 sw=4 et +% +\xchapter{inslist}{\textindexlc{Instruction List}} + +\xsection{inslistintro}{Introduction} + +The following sections show the instructions which NASM currently supports. For each +instruction, there is a separate entry for each supported addressing mode. The third +column shows the processor type in which the instruction was introduced and, +when appropriate, one or more usage flags. + +% +% FIXME: Read instruction list diff --git a/doc/latex/src/intro.tex b/doc/latex/src/intro.tex new file mode 100644 index 00000000..78c0946e --- /dev/null +++ b/doc/latex/src/intro.tex @@ -0,0 +1,55 @@ +% +% vim: ts=4 sw=4 et +% +\xchapter{intro}{Introduction} + +\xsection{whatis}{What Is NASM?} + +The Netwide Assembler, NASM, is an 80x86 and x86-64 assembler designed +for portability and modularity. It supports a range of object file +formats, including Linux and ``*BSD a.out'', ``ELF'', ``COFF'', +``Mach-O'', 16-bit and 32-bit ``OBJ'' (OMF) format, ``Win32'' and +``Win64''. It will also output plain binary files, Intel hex and +Motorola S-Record formats. Its syntax is designed to be simple and +easy to understand, similar to the syntax in the Intel Software +Developer Manual with minimal complexity. It supports all currently +known x86 architectural extensions, and has strong support for macros. + +NASM also comes with a set of utilities for handling the ``RDOFF'' +custom object-file format. + +\xsection{license}{License Conditions} + +Please see the file \index{license} ``LICENSE'', supplied as part +of any NASM distribution archive, for the license conditions under +which you may use NASM. NASM is now under the so-called 2-clause +BSD license, also known as the simplified BSD license. + +Copyright 1996-2017 the NASM Authors - All rights reserved. + +Redistribution and use in source and binary forms, with or without +modification, are permitted provided that the following conditions are +met: + +\begin{itemize} + \item{Redistributions of source code must retain the above copyright + notice, this list of conditions and the following disclaimer.} + + \item{Redistributions in binary form must reproduce the above copyright + notice, this list of conditions and the following disclaimer in the + documentation and/or other materials provided with the distribution.} +\end{itemize} + +THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND +CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, +INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF +MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE +DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR +CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT +NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; +LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) +HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN +CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR +OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, +EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. diff --git a/doc/latex/src/language.tex b/doc/latex/src/language.tex new file mode 100644 index 00000000..e29b8381 --- /dev/null +++ b/doc/latex/src/language.tex @@ -0,0 +1,945 @@ +% +% vim: ts=4 sw=4 et +% +\xchapter{lang}{The NASM Language} + +\xsection{syntax}{Layout of a NASM Source Line} + +Like most assemblers, each NASM source line contains (unless it +is a macro, a preprocessor directive or an assembler directive: see +\nref{preproc} and \nref{directive}) some combination +of the four fields + +\begin{lstlisting} +label: instruction operands ; comment +\end{lstlisting} + +As usual, most of these fields are optional; the presence or absence +of any combination of a label, an instruction and a comment is allowed. +Of course, the operand field is either required or forbidden by the +presence and nature of the instruction field. + +NASM uses backslash (\code{\textbackslash}) as the line continuation character; +if a line ends with backslash, the next line is considered to be +a part of the backslash-ended line. + +NASM places no restrictions on white space within a line: labels may +have white space before them, or instructions may have no space +before them, or anything. The \textindex{colon} after a label is also +optional. (Note that this means that if you intend to code \code{lodsb} +alone on a line, and type \code{lodab} by accident, then that's still a +valid source line which does nothing but define a label. Running +NASM with the command-line option \index{orphan-labels}\code{-w+orphan-labels} +will cause it to warn you if you define a label alone on a line without +a \textindex{trailing colon}.) + +\textindex{Valid characters} in labels are letters, numbers, \code{\_}, +\code{\$}, \code{\#}, \code{\@}, \code{~}, \code{.}, and \code{?}. +The only characters which may be used as the \emph{first} character of +an identifier are letters, \code{\.} (with special meaning: see +\nref{locallab}), \code{\_} and \code{?}. +An identifier may also be prefixed with a \codeindex{\$} to indicate +that it is intended to be read as an identifier and not a reserved word; +thus, if some other module you are linking with defines a symbol called +\code{eax}, you can refer to \code{\$eax} in NASM code to distinguish +the symbol from the register. Maximum length of an identifier is +4095 characters. + +The instruction field may contain any machine instruction: Pentium +and P6 instructions, FPU instructions, MMX instructions and even +undocumented instructions are all supported. The instruction may be +prefixed by \code{LOCK}, \code{REP}, \code{REPE}/\code{REPZ}, +\code{REPNE}/\code{REPNZ}, \code{XACQUIRE}/\code{XRELEASE} or +\code{BND}/\code{NOBND}, in the usual way. Explicit +\index{address-size!prefixes}address-size and \textindex{operand-size!prefixes} +\codeindex{A16}, \codeindex{A32}, \codeindex{A64}, \codeindex{O16} +and \codeindex{O32}, \codeindex{O64} are provided~-- one example of their +use is given in \nref{mixsize}. You can also use the name of a +\index{segment override}segment register as an instruction prefix: coding +\code{es mov [bx],ax} is equivalent to coding \code{mov [es:bx],ax}. +We recommend the latter syntax, since it is consistent with other syntactic +features of the language, but for instructions such as \code{LODSB}, which +has no operands and yet can require a segment override, there is no clean +syntactic way to proceed apart from \code{es lodsb}. + +An instruction is not required to use a prefix: prefixes such as +\code{CS}, \code{A32}, \code{LOCK} or \code{REPE} can appear on +a line by themselves, and NASM will just generate the prefix bytes. + +In addition to actual machine instructions, NASM also supports a +number of pseudo-instructions, described in \k{pseudop}. + +Instruction \textindex{operands} may take a number of forms: they can be +registers, described simply by the register name (e.g. \code{ax}, +\code{bp}, \code{ebx}, \code{cr0}: NASM does not use the \code{gas}-style +syntax in which register names must be prefixed by a \code{\%} sign), +or they can be \textindex{effective addresses} (see \nref{effaddr}), +constants (\nref{const}) or expressions (\nref{expr}). + +For x87 \textindex{floating-point} instructions, NASM accepts a wide +range of syntaxes: you can use two-operand forms like MASM supports, +or you can use NASM's native single-operand forms in most cases. +% Details of all forms of each supported instruction are given in +% \nref{iref}. +For example, you can code: + +\begin{lstlisting} +fadd st1 ; this sets st0 := st0 + st1 +fadd st0,st1 ; so does this + +fadd st1,st0 ; this sets st1 := st1 + st0 +fadd to st1 ; so does this +\end{lstlisting} + +Almost any x87 floating-point instruction that references memory must +use one of the prefixes \codeindex{DWORD}, \codeindex{QWORD} or +\codeindex{TWORD} to indicate what size of \textindex{memory operand} +it refers to. + +\xsection{pseudop}{\textindexlc{Pseudo-Instructions}} + +Pseudo-instructions are things which, though not real x86 machine +instructions, are used in the instruction field anyway because that's +the most convenient place to put them. The current pseudo-instructions +are \codeindex{DB}, \codeindex{DW}, \codeindex{DD}, \codeindex{DQ}, +\codeindex{DT}, \codeindex{DO}, \codeindex{DY} and \codeindex{DZ}; +their \textindex{uninitialized} counterparts \codeindex{RESB}, +\codeindex{RESW}, \codeindex{RESD}, \codeindex{RESQ}, +\codeindex{REST}, \codeindex{RESO}, \codeindex{RESY} and +\codeindex{RESZ}; the \codeindex{INCBIN} command, the \codeindex{EQU} +command, and the \codeindex{TIMES} prefix. + +\xsubsection{db}{DB and Friends: Declaring Initialized Data} + +\codeindex{DB}, \codeindex{DW}, \codeindex{DD}, \codeindex{DQ}, +\codeindex{DT}, \codeindex{DO}, \codeindex{DY} and \codeindex{DZ} +are used, much as in MASM, to declare initialized data in +the output file. They can be invoked in a wide range of ways: +\index{constants!floating-point} +\index{constants!character} +\index{constants!string} + +\begin{lstlisting} +db 0x55 ; just the byte 0x55 +db 0x55,0x56,0x57 ; three bytes in succession +db 'a',0x55 ; character constants are OK +db 'hello',13,10,'$' ; so are string constants +dw 0x1234 ; 0x34 0x12 +dw 'a' ; 0x61 0x00 (it's just a number) +dw 'ab' ; 0x61 0x62 (character constant) +dw 'abc' ; 0x61 0x62 0x63 0x00 (string) +dd 0x12345678 ; 0x78 0x56 0x34 0x12 +dd 1.234567e20 ; floating-point constant +dq 0x123456789abcdef0 ; eight byte constant +dq 1.234567e20 ; double-precision float +dt 1.234567e20 ; extended-precision float +\end{lstlisting} + +\code{DT}, \code{DO}, \code{DY} and \code{DZ} do not accept +numeric constants as operands. +\index{constants!numeric} + +\xsubsection{resb}{RESB and Friends: Declaring \textindexlc{Uninitialized} Data} + +\codeindex{RESB}, \codeindex{RESW}, \codeindex{RESD}, \codeindex{RESQ}, +\codeindex{REST}, \codeindex{RESO}, \codeindex{RESY} and \codeindex{RESZ} +are designed to be used in the BSS section of a module: they declare +\emph{uninitialized} storage space. Each takes a single operand, which is +the number of bytes, words, doublewords or whatever to reserve. As stated +in \nref{qsother}, NASM does not support the MASM/TASM syntax of +reserving uninitialized space by writing \index{?}\code{DW ?} or similar +things: this is what it does instead. The operand to a \code{RESB}-type +pseudo-instruction is a \textindex{critical expression}: +see \nref{crit}. + +For example: + +\begin{lstlisting} +buffer: resb 64 ; reserve 64 bytes +wordvar: resw 1 ; reserve a word +realarray resq 10 ; array of ten reals +ymmval: resy 1 ; one YMM register +zmmvals: resz 32 ; 32 ZMM registers +\end{lstlisting} + +\xsubsection{incbin}{\codeindex{INCBIN}: Including External \textindexlc{Binary Files}} + +\code{INCBIN} is borrowed from the old Amiga assembler \textindex{DevPac}: +it includes a binary file verbatim into the output file. This can be handy +for (for example) including \textindex{graphics} and \textindex{sound} data +directly into a game executable file. It can be called in one of these +three ways: + +\begin{lstlisting} +incbin "file.dat" ; include the whole file +incbin "file.dat",1024 ; skip the first 1024 bytes +incbin "file.dat",1024,512 ; skip the first 1024, and +\end{lstlisting} + +\code{INCBIN} is both a directive and a standard macro; the standard +macro version searches for the file in the include file search path +and adds the file to the dependency lists. This macro can be +overridden if desired. + +\xsubsection{equ}{\codeindex{EQU}: Defining Constants} + +\code{EQU} defines a symbol to a given constant value: when \code{EQU} is +used, the source line must contain a label. The action of \code{EQU} is +to define the given label name to the value of its (only) operand. +This definition is absolute, and cannot change later. So, for +example, + +\begin{lstlisting} +message db 'hello, world' +msglen equ $-message +\end{lstlisting} + +defines \code{msglen} to be the constant 12. \code{msglen} may +not then be redefined later. This is not a \textindex{preprocessor} +definition either: the value of \code{msglen} is evaluated \code{once}, +using the value of \code{\$} (see \nref{expr} for an explanation +of \code{\$}) at the point of definition, rather than being evaluated +wherever it is referenced and using the value of \code{\$} at +the point of reference. + +\xsubsection{times}{\codeindex{TIMES}: \textindexlc{Repeating} Instructions or Data} + +The \code{TIMES} prefix causes the instruction to be assembled multiple +times. This is partly present as NASM's equivalent of the \codeindex{DUP} +syntax supported by \textindex{MASM}-compatible assemblers, in that you can +code + +\begin{lstlisting} +zerobuf: times 64 db 0 +\end{lstlisting} + +or similar things; but \code{TIMES} is more versatile than that. The +argument to \code{TIMES} is not just a numeric constant, but a numeric +\emph{expression}, so you can do things like + +\begin{lstlisting} +buffer: db 'hello, world' + times 64-$+buffer db ' ' +\end{lstlisting} + +which will store exactly enough spaces to make the total length of +\code{buffer} up to 64. Finally, \code{TIMES} can be applied to ordinary +instructions, so you can code trivial \textindex{unrolled loops} in it: + +\begin{lstlisting} +times 100 movsb +\end{lstlisting} + +Note that there is no effective difference between \code{times 100 resb +1} and \code{resb 100}, except that the latter will be assembled about +100 times faster due to the internal structure of the assembler. + +The operand to \code{TIMES} is a critical expression (\nref{crit}). + +Note also that \code{TIMES} can't be applied to \textindex{macros}: the reason +for this is that \code{TIMES} is processed after the macro phase, which +allows the argument to \code{TIMES} to contain expressions such as +\code{64-\$+buffer} as above. To repeat more than one line of code, +or a complex macro, use the preprocessor \codeindex{\%rep} directive. + +\xsection{effaddr}{Effective Addresses} + +An \textindex{effective address} is any operand to an instruction which +\index{memory reference}references memory. Effective addresses, in NASM, +have a very simple syntax: they consist of an expression evaluating +to the desired address, enclosed in \textindex{square brackets}. For +example: + +\begin{lstlisting} +wordvar dw 123 + mov ax,[wordvar] + mov ax,[wordvar+1] + mov ax,[es:wordvar+bx] +\end{lstlisting} + +Anything not conforming to this simple system is not a valid memory +reference in NASM, for example \code{es:wordvar[bx]}. + +More complicated effective addresses, such as those involving more +than one register, work in exactly the same way: + +\begin{lstlisting} +mov eax,[ebx*2+ecx+offset] +mov ax,[bp+di+8] +\end{lstlisting} + +NASM is capable of doing \textindex{algebra} on these effective addresses, +so that things which don't necessarily \emph{look} legal are perfectly +all right: + +\begin{lstlisting} +mov eax,[ebx*5] ; assembles as [ebx*4+ebx] +mov eax,[label1*2-label2] ; ie [label1+(label1-label2)] +\end{lstlisting} + +Some forms of effective address have more than one assembled form; +in most such cases NASM will generate the smallest form it can. For +example, there are distinct assembled forms for the 32-bit effective +addresses \code{[eax*2+0]} and \code{[eax+eax]}, and NASM will +generally generate the latter on the grounds that the former requires +four bytes to store a zero offset. + +NASM has a hinting mechanism which will cause \code{[eax+ebx]} and +\code{[ebx+eax]} to generate different opcodes; this is occasionally +useful because \code{[esi+ebp]} and \code{[ebp+esi]} have different +default segment registers. + +However, you can force NASM to generate an effective address in a +particular form by the use of the keywords \code{BYTE}, \code{WORD}, +\code{DWORD} and \code{NOSPLIT}. If you need \code{[eax+3]} to be +assembled using a double-word offset field instead of the one byte NASM +will normally generate, you can code \code{[dword eax+3]}. Similarly, you +can force NASM to use a byte offset for a small value which it hasn't seen +on the first pass (see \nref{crit} for an example of such a code +fragment) by using \code{[byte eax+offset]}. As special cases, \code{[byte eax]} +will code \code{[eax+0]} with a byte offset of zero, and \code{[dword eax]} +will code it with a double-word offset of zero. The normal form, \code{[eax]}, +will be coded with no offset field. + +The form described in the previous paragraph is also useful if you +are trying to access data in a 32-bit segment from within 16 bit code. +For more information on this see the section on mixed-size addressing +(\nref{mixaddr}). In particular, if you need to access data with +a known offset that is larger than will fit in a 16-bit value, if you don't +specify that it is a dword offset, nasm will cause the high word of +the offset to be lost. + +Similarly, NASM will split \code{[eax*2]} into \code{[eax+eax]} because +that allows the offset field to be absent and space to be saved; in fact, +it will also split \code{[eax*2+offset]} into \code{[eax+eax+offset]}. +You can combat this behaviour by the use of the \code{NOSPLIT} keyword: +\code{[nosplit eax*2]} will force \code{[eax*2+0]} to be generated literally. +\code{[nosplit eax*1]} also has the same effect. In another way, a split EA +form \code{[0, eax*2]} can be used, too. However, \code{NOSPLIT} in +\code{[nosplit eax+eax]} will be ignored because user's intention here +is considered as \code{[eax+eax]}. + +In 64-bit mode, NASM will by default generate absolute addresses. The +\codeindex{REL} keyword makes it produce \code{RIP}-relative addresses. +Since this is frequently the normally desired behaviour, see the \code{DEFAULT} +directive (\nref{default}). The keyword \codeindex{ABS} overrides +\codeindex{REL}. + +A new form of split effective addres syntax is also supported. This is +mainly intended for mib operands as used by MPX instructions, but can +be used for any memory reference. The basic concept of this form is +splitting base and index. + +\begin{lstlisting} +mov eax,[ebx+8,ecx*4] ; ebx=base, ecx=index, 4=scale, 8=disp +\end{lstlisting} + +For mib operands, there are several ways of writing effective address +depending on the tools. NASM supports all currently possible ways of +mib syntax: + +\begin{lstlisting} +; bndstx +; next 5 lines are parsed same +; base=rax, index=rbx, scale=1, displacement=3 +bndstx [rax+0x3,rbx], bnd0 ; NASM - split EA +bndstx [rbx*1+rax+0x3], bnd0 ; GAS - '*1' indecates an index reg +bndstx [rax+rbx+3], bnd0 ; GAS - without hints +bndstx [rax+0x3], bnd0, rbx ; ICC-1 +bndstx [rax+0x3], rbx, bnd0 ; ICC-2 +\end{lstlisting} + +When broadcasting decorator is used, the opsize keyword should match +the size of each element. + +\begin{lstlisting} +vdivps zmm4, zmm5, dword [rbx]{1to16} ; single-precision float +vdivps zmm4, zmm5, zword [rbx] ; packed 512 bit memory +\end{lstlisting} + +\xsection{const}{\textindexlc{Constants}} + +NASM understands four different types of constant: numeric, +character, string and floating-point. + +\xsubsection{numconst}{Numeric Constants} +\index{constants!numeric} +\index{constants!hexadecimal} +\index{constants!decimal} +\index{constants!octal} +\index{constants!binary} + +A numeric constant is simply a number. NASM allows you to specify +numbers in a variety of number bases, in a variety of ways: you can +suffix \code{H} or \code{X}, \code{D} or \code{T}, \code{Q} or +\code{O}, and \code{B} or \code{Y} for hexadecimal, decimal, octal and +binary respectively, or you can prefix \code{0x}, for hexadecimal in +the style of C, or you can prefix \code{\$} for hexadecimal in the style +of Borland Pascal or Motorola Assemblers. Note, though, that the \index{prefix} +\codeindex{\$} prefix does double duty as a prefix on identifiers (see \nref{syntax}), +so a hex number prefixed with a \code{\$} sign must have a digit after the +\code{\$} rather than a letter. In addition, current versions of NASM accept +the prefix \code{0h} for hexadecimal, \code{0d} or \code{0t} for decimal, +\code{0o} or \code{0q} for octal, and \code{0b} or \code{0y} for binary. +Please note that unlike C, a \code{0} prefix by itself does \emph{not} imply +an octal constant! + +Numeric constants can have underscores (\code{\_}) interspersed to break +up long strings. + +Some examples (all producing exactly the same code): + +\begin{lstlisting} +mov ax,200 ; decimal +mov ax,0200 ; still decimal +mov ax,0200d ; explicitly decimal +mov ax,0d200 ; also decimal +mov ax,0c8h ; hex +mov ax,$0c8 ; hex again: the 0 is required +mov ax,0xc8 ; hex yet again +mov ax,0hc8 ; still hex +mov ax,310q ; octal +mov ax,310o ; octal again +mov ax,0o310 ; octal yet again +mov ax,0q310 ; octal yet again +mov ax,11001000b ; binary +mov ax,1100_1000b ; same binary constant +mov ax,1100_1000y ; same binary constant once more +mov ax,0b1100_1000 ; same binary constant yet again +mov ax,0y1100_1000 ; same binary constant yet again +\end{lstlisting} + +\xsubsection{strings}{\index{strings}Character Strings} + +A character string consists of up to eight characters enclosed in +either single quotes (\code{'...'}), double quotes (\code{"..."}) or +backquotes (\code{`...`}). Single or double quotes are equivalent to +NASM (except of course that surrounding the constant with single +quotes allows double quotes to appear within it and vice versa); the +contents of those are represented verbatim. Strings enclosed in +backquotes support C-style \code{\textbackslash}-escapes for +special characters. + +The following \textindex{escape sequences} are recognized by +backquoted strings: + +\begin{lstlisting} +\' single quote (') +\" double quote (") +\` backquote (`) +\\ backslash (\) +\? question mark (?) +\a BEL (ASCII 7) +\b BS (ASCII 8) +\t TAB (ASCII 9) +\n LF (ASCII 10) +\v VT (ASCII 11) +\f FF (ASCII 12) +\r CR (ASCII 13) +\e ESC (ASCII 27) +\377 Up to 3 octal digits - literal byte +\xFF Up to 2 hexadecimal digits - literal byte +\u1234 4 hexadecimal digits - Unicode character +\U12345678 8 hexadecimal digits - Unicode character +\end{lstlisting} + +All other escape sequences are reserved. Note that \code{\textbackslash 0}, +meaning a \code{NUL} character (ASCII 0), is a special case of +the octal escape sequence. + +\textindex{Unicode} characters specified with \code{\textbackslash u} +or \code{\textbackslash U} are converted to \textindex{UTF-8}. +For example, the following lines are all equivalent: + +\begin{lstlisting} +db `\u263a` ; UTF-8 smiley face +db `\xe2\x98\xba` ; UTF-8 smiley face +db 0E2h, 098h, 0BAh ; UTF-8 smiley face +\end{lstlisting} + +\xsubsection{chrconst}{Character Constants} +\index{constants!character} + +A character constant consists of a string up to eight bytes long, used +in an expression context. It is treated as if it was an integer. + +A character constant with more than one byte will be arranged +with \textindex{little-endian} order in mind: if you code + +\begin{lstlisting} +mov eax,'abcd' +\end{lstlisting} + +then the constant generated is not \code{0x61626364}, but \code{0x64636261}, +so that if you were then to store the value into memory, it would read +\code{abcd} rather than \code{dcba}. This is also the sense of character +constants understood by the Pentium's \codeindex{CPUID} instruction. + +\xsubsection{strconst}{String Constants} +\index{constants!string} + +String constants are character strings used in the context of some +pseudo-instructions, namely the \indexcode{DW}\indexcode{DD}\indexcode{DQ} +\indexcode{DT}\indexcode{DO}\indexcode{DY}\codeindex{DB} family and +\codeindex{INCBIN} (where it represents a filename.) They are also used in +certain preprocessor directives. + +A string constant looks like a character constant, only longer. It +is treated as a concatenation of maximum-size character constants +for the conditions. So the following are equivalent: + +\begin{lstlisting} +db 'hello' ; string constant +db 'h','e','l','l','o' ; equivalent character constants +\end{lstlisting} + +And the following are also equivalent: + +\begin{lstlisting} +dd 'ninechars' ; doubleword string constant +dd 'nine','char','s' ; becomes three doublewords +db 'ninechars',0,0,0 ; and really looks like this +\end{lstlisting} + +Note that when used in a string-supporting context, quoted strings are +treated as a string constants even if they are short enough to be a +character constant, because otherwise \code{db 'ab'} would have the same +effect as \code{db 'a'}, which would be silly. Similarly, three-character +or four-character constants are treated as strings when they are +operands to \code{DW}, and so forth. + +\xsubsection{unicode}{Unicode Constants} +\index{constants!unicode} +\index{UTF-16} +\index{UTF-32} + +The special operators \codeindex{\_\_utf16\_\_}, \codeindex{\_\_utf16le\_\_}, +\codeindex{\_\_utf16be\_\_}, \codeindex{\_\_utf32\_\_}, \codeindex{\_\_utf32le\_\_} +and \codeindex{\_\_utf32be\_\_} allows definition of Unicode strings. +They take a string in UTF-8 format and converts it to UTF-16 or UTF-32, +respectively. Unless the \code{be} forms are specified, the output is +littleendian. + +For example: + +\begin{lstlisting} +%define u(x) __utf16__(x) +%define w(x) __utf32__(x) + + dw u('C:\WINDOWS'), 0 ; Pathname in UTF-16 + dd w(`A + B = \u206a`), 0 ; String in UTF-32 +\end{lstlisting} + +The UTF operators can be applied either to strings passed to the +\code{DB} family instructions, or to character constants in an expression +context. + +\xsubsection{fltconst}{Floating-Point Constants} +\index{constants!floating-point} + +\textindexlc{Floating-point} constants are acceptable only as arguments to +\codeindex{DB}, \codeindex{DW}, \codeindex{DD}, \codeindex{DQ}, \codeindex{DT}, +and \codeindex{DO}, or as arguments to the special operators \codeindex{\_\_float8\_\_}, +\codeindex{\_\_float16\_\_}, \codeindex{\_\_float32\_\_}, \codeindex{\_\_float64\_\_}, +\codeindex{\_\_float80m\_\_}, \codeindex{\_\_float80e\_\_}, \codeindex{\_\_float128l\_\_}, +and \codeindex{\_\_float128h\_\_}. + +Floating-point constants are expressed in the traditional form: +digits, then a period, then optionally more digits, then optionally an +\code{E} followed by an exponent. The period is mandatory, so that NASM +can distinguish between \code{dd 1}, which declares an integer constant, +and \code{dd 1.0} which declares a floating-point constant. + +NASM also support C99-style hexadecimal floating-point: \code{0x}, +hexadecimal digits, period, optionally more hexadeximal digits, then +optionally a \code{P} followed by a \emph{binary} (not hexadecimal) +exponent in decimal notation. As an extension, NASM additionally +supports the \code{0h} and \code{\$} prefixes for hexadecimal, +as well binary and octal floating-point, using the \code{0b} or +\code{0y} and \code{0o} or \code{0q} prefixes, respectively. + +Underscores to break up groups of digits are permitted in +floating-point constants as well. + +Some examples: + +\begin{lstlisting} +db -0.2 ; "Quarter precision" +dw -0.5 ; IEEE 754r/SSE5 half precision +dd 1.2 ; an easy one +dd 1.222_222_222 ; underscores are permitted +dd 0x1p+2 ; 1.0x2^2 = 4.0 +dq 0x1p+32 ; 1.0x2^32 = 4 294 967 296.0 +dq 1.e10 ; 10 000 000 000.0 +dq 1.e+10 ; synonymous with 1.e10 +dq 1.e-10 ; 0.000 000 000 1 +dt 3.141592653589793238462 ; pi +do 1.e+4000 ; IEEE 754r quad precision +\end{lstlisting} + +The 8-bit "quarter-precision" floating-point format is +sign:exponent:mantissa = 1:4:3 with an exponent bias of 7. This +appears to be the most frequently used 8-bit floating-point format, +although it is not covered by any formal standard. This is sometimes +called a ``\textindex{minifloat}''. + +The special operators are used to produce floating-point numbers in +other contexts. They produce the binary representation of a specific +floating-point number as an integer, and can use anywhere integer +constants are used in an expression. \code{\_\_float80m\_\_} and +\code{\_\_float80e\_\_} produce the 64-bit mantissa and 16-bit +exponent of an 80-bit floating-point number, and \code{\_\_float128l\_\_} +and \code{\_\_float128h\_\_} produce the lower and upper 64-bit halves +of a 128-bit floating-point number, respectively. + +For example: + +\begin{lstlisting} +mov rax,__float64__(3.141592653589793238462) +\end{lstlisting} + +would assign the binary representation of pi as a 64-bit floating +point number into \code{RAX}. This is exactly equivalent to: + +\begin{lstlisting} +mov rax,0x400921fb54442d18 +\end{lstlisting} + +NASM cannot do compile-time arithmetic on floating-point constants. +This is because NASM is designed to be portable - although it always +generates code to run on x86 processors, the assembler itself can +run on any system with an ANSI C compiler. Therefore, the assembler +cannot guarantee the presence of a floating-point unit capable of +handling the \textindexlc{Intel number formats}, and so for NASM +to be able to do floating arithmetic it would have to include its +own complete set of floating-point routines, which would significantly +increase the size of the assembler for very little benefit. + +The special tokens \codeindex{\_\_Infinity\_\_}, \codeindex{\_\_QNaN\_\_} (or +\codeindex{\_\_NaN\_\_}) and \codeindex{\_\_SNaN\_\_} can be used to generate +\index{infinity}infinities, quiet \textindex{NaN}s, and signalling NaNs, +respectively. These are normally used as macros: + +\begin{lstlisting} +%define Inf __Infinity__ +%define NaN __QNaN__ + + dq +1.5, -Inf, NaN ; Double-precision constants +\end{lstlisting} + +The \code{\%use fp} standard macro package contains a set of convenience +macros. See \nref{pkgfp}. + +\xsubsection{bcdconst}{Packed BCD Constants} +\index{constants!packed BCD} + +x87-style packed BCD constants can be used in the same contexts as +80-bit floating-point numbers. They are suffixed with \code{p} or +prefixed with \code{0p}, and can include up to 18 decimal digits. + +As with other numeric constants, underscores can be used +to separate digits. + +For example: + +\begin{lstlisting} +dt 12_345_678_901_245_678p +dt -12_345_678_901_245_678p +dt +0p33 +dt 33p +\end{lstlisting} + +\xsection{expr}{\textindex{Expressions}} + +Expressions in NASM are similar in syntax to those in C. Expressions +are evaluated as 64-bit integers which are then adjusted to the +appropriate size. + +NASM supports two special tokens in expressions, allowing +calculations to involve the current assembly position: the +\index{\$}\index{here}\code{\$} and \codeindex{\$\$} tokens. +\code{\$} evaluates to the assembly position at the beginning +of the line containing the expression; so you can code an +\textindex{infinite loop} using \code{JMP \$}. \code{\$\$} +evaluates to the beginning of the current section; so you can +tell how far into the section you are by using \code{(\$-\$\$)}. + +The arithmetic \textindex{operators} provided by NASM are listed here, +in increasing order of \textindex{precedence}. + +\xsubsection{expor}{\codeindex{|}: Bitwise OR Operator} +\index{bitwise!OR} + +The \code{|} operator gives a bitwise OR, exactly as performed by the +\code{OR} machine instruction. Bitwise OR is the lowest-priority +arithmetic operator supported by NASM. + +\xsubsection{expxor}{\codeindex{\textasciicircum}: Bitwise XOR Operator} +\index{bitwise!XOR} + +The \code{\textasciicircum} operator provides the bitwise XOR operation. + +\xsubsection{expand}{\codeindex{\&}: Bitwise AND Operator} +\index{bitwise!AND} + +The \code{\&} operator provides the bitwise AND operation. + +\xsubsection{expshift}{\codeindex{<<} and \codeindex{>>}: \textindexlc{Bit Shift} Operators} + +\code{<<} gives a bit-shift to the left, just as it does in C. +So \code{5<<3} evaluates to 5 times 8, or 40. \code{>>} gives +a bit-shift to the right; in NASM, such a shift is \emph{always} +unsigned, so that the bits shifted in from the left-hand end +are filled with zero rather than a sign-extension of the +previous highest bit. + +\xsubsection{expplmi}{\codeindex{+} and \codeindex{-}: +\textindexlc{Addition} and \textindexlc{Subtraction} Operators} + +The \code{+} and \code{-} operators do perfectly ordinary addition +and subtraction. + +\xsubsection{expmul}{\codeindex{*}, \codeindex{/}, +\codeindex{//} and \codeindex{\%\%}: +\textindexlc{Multiplication} and \textindexlc{Division}} + +\code{*} is the multiplication operator. \code{/} and \code{//} are both +division operators: \code{/} is \textindex{unsigned division} and +\code{//} is \textindex{signed division}. Similarly, \code{\%} and +\code{\%\%} provide \index{unsigned modulo}\index{modulo operators}unsigned +and \textindex{signed modulo} operators respectively. + +NASM, like ANSI C, provides no guarantees about the sensible +operation of the signed modulo operator. + +Since the \code{\%} character is used extensively by the macro +\textindex{preprocessor}, you should ensure that both the signed +and unsigned modulo operators are followed by white space wherever +they appear. + +\xsubsection{expunary}{\textindex{Unary Operators}} +\index{unary!+} +\index{unary!-} +\index{unary!\textasciitilde} +\index{unary!seg} + +The highest-priority operators in NASM's expression grammar are those +which only apply to one argument. These are \codeindex{+}, +\codeindex{-}, \codeindex{\textasciitilde}, \codeindex{!}, +\codeindex{SEG}, and the \textindex{integer functions} operators. + +\code{-} negates its operand, \code{+} does nothing (it's provided for +symmetry with \code{-}), \code{\textasciitilde} computes the +\textindex{one's complement} of its operand, \code{!} is the +\textindex{logical negation} operator. + +\code{SEG} provides the \textindex{segment address} +of its operand (explained in more detail in \nref{segwrt}). + +A set of additional operators with leading and trailing double +underscores are used to implement the integer functions of the +\code{ifunc} macro package, see \nref{pkgifunc}. + +\xsection{segwrt}{\codeindex{SEG} and \codeindex{WRT}} + +When writing large 16-bit programs, which must be split into +multiple \textindex{segments}, it is often necessary to be able +to refer to the \index{segment address}segment part of the address +of a symbol. NASM supports the \code{SEG} operator to perform +this function. + +The \code{SEG} operator returns the \emph{\textindex{preferred}} +segment base of a symbol, defined as the segment base relative +to which the offset of the symbol makes sense. So the code + +\begin{lstlisting} +mov ax,seg symbol +mov es,ax +mov bx,symbol +\end{lstlisting} + +will load \code{ES:BX} with a valid pointer to the symbol +\code{symbol}. + +Things can be more complex than this: since 16-bit segments and +\textindex{groups} may \index{overlapping segments}overlap, +you might occasionally want to refer to some symbol using +a different segment base from the preferred one. NASM lets you +do this, by the use of the \code{WRT} (With Reference To) keyword. +So you can do things like + +\begin{lstlisting} +mov ax,weird_seg ; weird_seg is a segment base +mov es,ax +mov bx,symbol wrt weird_seg +\end{lstlisting} + +to load \code{ES:BX} with a different, but functionally equivalent, +pointer to the symbol \code{symbol}. + +NASM supports far (inter-segment) calls and jumps by means of the +syntax \code{call segment:offset}, where \code{segment} +and \code{offset} both represent immediate values. So to call +a far procedure, you could code either of + +\begin{lstlisting} +call (seg procedure):procedure +call weird_seg:(procedure wrt weird_seg) +\end{lstlisting} + +(The parentheses are included for clarity, to show the intended +parsing of the above instructions. They are not necessary in +practice.) + +NASM supports the syntax \indexcode{CALL FAR}\code{call far procedure} +as a synonym for the first of the above usages. \code{JMP} works +identically to \code{CALL} in these examples. + +To declare a \textindex{far pointer} to a data item in a data +segment, you must code + +\begin{lstlisting} +dw symbol, seg symbol +\end{lstlisting} + +NASM supports no convenient synonym for this, though you can always +invent one using the macro processor. + +\xsection{strict}{\codeindex{STRICT}: Inhibiting Optimization} + +When assembling with the optimizer set to level 2 or higher (see +\nref{opt-O}), NASM will use size specifiers (\code{BYTE}, +\code{WORD}, \code{DWORD}, \code{QWORD}, \code{TWORD}, \code{OWORD}, +\code{YWORD} or \code{ZWORD}), but will give them the smallest possible +size. The keyword \code{STRICT} can be used to inhibit optimization +and force a particular operand to be emitted in the specified size. +For example, with the optimizer on, and in \code{BITS 16} mode, + +\begin{lstlisting} +push dword 33 +\end{lstlisting} + +is encoded in three bytes \code{66 6A 21}, whereas + +\begin{lstlisting} +push strict dword 33 +\end{lstlisting} + +is encoded in six bytes, with a full dword immediate operand +\code{66 68 21 00 00 00}. + +With the optimizer off, the same code (six bytes) is generated whether +the \code{STRICT} keyword was used or not. + +\xsection{crit}{\textindexlc{Critical Expressions}} + +Although NASM has an optional multi-pass optimizer, there are some +expressions which must be resolvable on the first pass. These are +called \emph{Critical Expressions}. + +The first pass is used to determine the size of all the assembled +code and data, so that the second pass, when generating all the +code, knows all the symbol addresses the code refers to. So one +thing NASM can't handle is code whose size depends on the value +of a symbol declared after the code in question. For example, + +\begin{lstlisting} +times (label-$) db 0 +label: db 'Where am I?' +\end{lstlisting} + +The argument to \codeindex{TIMES} in this case could equally legally +evaluate to anything at all; NASM will reject this example because +it cannot tell the size of the \code{TIMES} line when it first sees it. +It will just as firmly reject the slightly \index{paradox}paradoxical +code + +\begin{lstlisting} +times (label-$+1) db 0 +label: db 'NOW where am I?' +\end{lstlisting} + +in which \emph{any} value for the \code{TIMES} argument +is by definition wrong! + +NASM rejects these examples by means of a concept called a +\emph{critical expression}, which is defined to be an +expression whose value is required to be computable in +the first pass, and which must therefore depend only +on symbols defined before it. The argument to the \code{TIMES} +prefix is a critical expression. + +\xsection{locallab}{\textindexlc{Local Labels}} + +NASM gives special treatment to symbols beginning with a \textindex{period}. +A label beginning with a single period is treated as a \emph{local} +label, which means that it is associated with the previous non-local +label. So, for example: + +\begin{lstlisting} +label1 ; some code + +.loop + ; some more code + + jne .loop + ret + +label2 ; some code + +.loop + ; some more code + + jne .loop + ret +\end{lstlisting} + +In the above code fragment, each \code{JNE} instruction jumps to the +line immediately before it, because the two definitions of +\code{.loop} are kept separate by virtue of each being associated +with the previous non-local label. + +This form of local label handling is borrowed from the old Amiga +assembler \textindex{DevPac}; however, NASM goes one step further, +in allowing access to local labels from other parts of the code. This +is achieved by means of \emph{defining} a local label in terms of the +previous non-local label: the first definition of \code{.loop} above is +really defining a symbol called \code{label1.loop}, and the second +defines a symbol called \code{label2.loop}. So, if you really needed +to, you could write + +\begin{lstlisting} +label3 ; some more code + ; and some more + + jmp label1.loop +\end{lstlisting} + +Sometimes it is useful - in a macro, for instance - to be able to +define a label which can be referenced from anywhere but which +doesn't interfere with the normal local-label mechanism. Such a +label can't be non-local because it would interfere with subsequent +definitions of, and references to, local labels; and it can't be +local because the macro that defined it wouldn't know the label's +full name. NASM therefore introduces a third type of label, which is +probably only useful in macro definitions: if a label begins with +the \index{label prefix}special prefix \codeindex{..@}, then it +does nothing to the local label mechanism. So you could code + +\begin{lstlisting} +label1: ; a non-local label +.local: ; this is really label1.local +..@foo: ; this is a special symbol +label2: ; another non-local label +.local: ; this is really label2.local + + jmp ..@foo ; this will jump three lines up +\end{lstlisting} + +NASM has the capacity to define other special symbols beginning with +a double period: for example, \code{..start} is used to specify the +entry point in the \code{obj} output format (see \nref{dotdotstart}), +\code{..imagebase} is used to find out the offset from a base address +of the current image in the \code{win64} output format +(see \nref{win64pic}). So just keep in mind that symbols +beginning with a double period are special. diff --git a/doc/latex/src/macropkg.tex b/doc/latex/src/macropkg.tex new file mode 100644 index 00000000..c71b548c --- /dev/null +++ b/doc/latex/src/macropkg.tex @@ -0,0 +1,127 @@ +% +% vim: ts=4 sw=4 et +% +\xchapter{macropkg}{\textindexlc{Standard Macro Packages}} + +The \codeindex{\%use} directive (see \nref{use}) includes one of +the standard macro packages included with the NASM distribution and compiled +into the NASM binary. It operates like the \code{\%include} directive (see +\nref{include}), but the included contents is provided by NASM itself. + +The names of standard macro packages are case insensitive, and can be +quoted or not. + +\xsection{pkgaltreg}{\codeindex{altreg}: \textindexlc{Alternate Register Names}} + +The \code{altreg} standard macro package provides alternate register +names. It provides numeric register names for all registers (not just +\code{R8}-\code{R15}), the Intel-defined aliases \code{R8L}-\code{R15L} +for the low bytes of register (as opposed to the NASM/AMD standard names +\code{R8B}-\code{R15B}), and the names \code{R0H}-\code{R3H} (by analogy +with \code{R0L}-\code{R3L}) for \code{AH}, \code{CH}, \code{DH}, +and \code{BH}. + +Example use: + +\begin{lstlisting} +%use altreg + +proc: + mov r0l,r3h ; mov al,bh + ret +\end{lstlisting} + +See also \nref{reg64}. + +\xsection{pkgsmartalign}{\codeindex{smartalign}\index{align, smart}: Smart \code{ALIGN} Macro} + +The \code{smartalign} standard macro package provides for an +\codeindex{ALIGN} macro which is more powerful than the default (and +backwards-compatible) one (see \nref{align}). When the +\code{smartalign} package is enabled, when \code{ALIGN} is used without +a second argument, NASM will generate a sequence of instructions more +efficient than a series of \code{NOP}. Furthermore, if the padding +exceeds a specific threshold, then NASM will generate a jump over +the entire padding sequence. + +The specific instructions generated can be controlled with the +new \codeindex{ALIGNMODE} macro. This macro takes two parameters: one mode, +and an optional jump threshold override. If (for any reason) you need +to turn off the jump completely just set jump threshold value to -1 +(or set it to \code{nojmp}). The following modes are possible: + +\begin{itemize} + \item{\code{generic}: Works on all x86 CPUs and should have + reasonable performance. The default jump threshold is 8. + This is the default.} + + \item{\code{nop}: Pad out with \code{NOP} instructions. The only + difference compared to the standard \code{ALIGN} macro is that NASM + can still jump over a large padding area. The default jump + threshold is 16.} + + \item{\code{k7}: Optimize for the AMD K7 (Athlon/Althon XP). + These instructions should still work on all x86 CPUs. The default + jump threshold is 16.} + + \item{\code{k8}: Optimize for the AMD K8 (Opteron/Althon 64). + These instructions should still work on all x86 CPUs. The default + jump threshold is 16.} + + \item{\code{p6}: Optimize for Intel CPUs. This uses the long + \code{NOP} instructions first introduced in Pentium Pro. This + is incompatible with all CPUs of family 5 or lower, as well as + some VIA CPUs and several virtualization solutions. The default + jump threshold is 16.} +\end{itemize} + +The macro \codeindex{\_\_ALIGNMODE\_\_} is defined to contain the +current alignment mode. A number of other macros beginning with +\code{\_\_ALIGN\_} are used internally by this macro package. + +\xsection{pkgfp}{\codeindex{fp}: Floating-point macros} + +This packages contains the following floating-point convenience macros: + +\begin{lstlisting} +%define Inf __Infinity__ +%define NaN __QNaN__ +%define QNaN __QNaN__ +%define SNaN __SNaN__ + +%define float8(x) __float8__(x) +%define float16(x) __float16__(x) +%define float32(x) __float32__(x) +%define float64(x) __float64__(x) +%define float80m(x) __float80m__(x) +%define float80e(x) __float80e__(x) +%define float128l(x) __float128l__(x) +%define float128h(x) __float128h__(x) +\end{lstlisting} + +\xsection{pkgifunc}{\codeindex{ifunc}: \textindexlc{Integer functions}} + +This package contains a set of macros which implement integer +functions. These are actually implemented as special operators, but +are most conveniently accessed via this macro package. + +\xsubsection{ilog2}{\textindexlc{Integer logarithms}} + +These functions calculate the integer logarithm base 2 of their +argument, considered as an unsigned integer. The only differences +between the functions is their respective behavior if the argument +provided is not a power of two. + +The function \codeindex{ilog2e()} (alias \codeindex{ilog2()}) generates +an error if the argument is not a power of two. + +The function \codeindex{ilog2f()} rounds the argument down to the nearest +power of two; if the argument is zero it returns zero. + +The function \codeindex{ilog2c()} rounds the argument up to the nearest +power of two. + +The functions \codeindex{ilog2fw()} (alias \codeindex{ilog2w()}) and +\codeindex{ilog2cw()} generate a warning if the argument is not a power of +two, but otherwise behaves like \codeindex{ilog2f()} and \codeindex{ilog2c()}, +respectively. diff --git a/doc/latex/src/mixsize.tex b/doc/latex/src/mixsize.tex new file mode 100644 index 00000000..b8a35ea8 --- /dev/null +++ b/doc/latex/src/mixsize.tex @@ -0,0 +1,185 @@ +% +% vim: ts=4 sw=4 et +% +\xchapter{mixsize}{Mixing 16 and 32 Bit Code} + +This chapter tries to cover some of the issues, largely related to +unusual forms of addressing and jump instructions, encountered when +writing operating system code such as protected-mode initialisation +routines, which require code that operates in mixed segment sizes, +such as code in a 16-bit segment trying to modify data in a 32-bit +one, or jumps between different-size segments. + +\xsection{mixjump}{Mixed-Size Jumps} +\index{jumps!mixed-size} +\index{operating system, writing} +\index{writing operating systems} + +The most common form of \textindex{mixed-size instruction} is the one +used when writing a 32-bit OS: having done your setup in 16-bit mode, +such as loading the kernel, you then have to boot it by switching into +protected mode and jumping to the 32-bit kernel start address. In a +fully 32-bit OS, this tends to be the \emph{only} mixed-size +instruction you need, since everything before it can be done in pure +16-bit code, and everything after it can be pure 32-bit. + +This jump must specify a 48-bit far address, since the target +segment is a 32-bit one. However, it must be assembled in a 16-bit +segment, so just coding, for example, + +\begin{lstlisting} +jmp 0x1234:0x56789ABC ; wrong! +\end{lstlisting} + +will not work, since the offset part of the address will be +truncated to \code{0x9ABC} and the jump will be an ordinary 16-bit far +one. + +The Linux kernel setup code gets round the inability of \code{as86} to +generate the required instruction by coding it manually, using +\code{DB} instructions. NASM can go one better than that, by actually +generating the right instruction itself. Here's how to do it right: + +\begin{lstlisting} +jmp dword 0x1234:0x56789ABC ; right +\end{lstlisting} + +\indexcode{JMP DWORD}The \code{DWORD} prefix (strictly speaking, +it should come \emph{after} the colon, since it is declaring the +\emph{offset} field to be a doubleword; but NASM will accept either +form, since both are unambiguous) forces the offset part to be treated +as far, in the assumption that you are deliberately writing a jump from +a 16-bit segment to a 32-bit one. + +You can do the reverse operation, jumping from a 32-bit segment to a +16-bit one, by means of the \code{WORD} prefix: + +\begin{lstlisting} +jmp word 0x8765:0x4321 ; 32 to 16 bit +\end{lstlisting} + +If the \code{WORD} prefix is specified in 16-bit mode, or the +\code{DWORD} prefix in 32-bit mode, they will be ignored, since each is +explicitly forcing NASM into a mode it was in anyway. + +\xsection{mixaddr}{Addressing Between Different-Size Segments} +\index{addressing!mixed-size} +\index{mixed-size addressing} + +If your OS is mixed 16 and 32-bit, or if you are writing a DOS +extender, you are likely to have to deal with some 16-bit segments +and some 32-bit ones. At some point, you will probably end up +writing code in a 16-bit segment which has to access data in a +32-bit segment, or vice versa. + +If the data you are trying to access in a 32-bit segment lies within +the first 64K of the segment, you may be able to get away with using +an ordinary 16-bit addressing operation for the purpose; but sooner +or later, you will want to do 32-bit addressing from 16-bit mode. + +The easiest way to do this is to make sure you use a register for +the address, since any effective address containing a 32-bit +register is forced to be a 32-bit address. So you can do + +\begin{lstlisting} +mov eax,offset_into_32_bit_segment_specified_by_fs +mov dword [fs:eax],0x11223344 +\end{lstlisting} + +This is fine, but slightly cumbersome (since it wastes an +instruction and a register) if you already know the precise offset +you are aiming at. The x86 architecture does allow 32-bit effective +addresses to specify nothing but a 4-byte offset, so why shouldn't +NASM be able to generate the best instruction for the purpose? + +It can. As in \nref{mixjump}, you need only prefix the address +with the \code{DWORD} keyword, and it will be forced to be a 32-bit +address: + +\begin{lstlisting} +mov dword [fs:dword my_offset],0x11223344 +\end{lstlisting} + +Also as in \nref{mixjump}, NASM is not fussy about whether the +\code{DWORD} prefix comes before or after the segment override, so +arguably a nicer-looking way to code the above instruction is + +\begin{lstlisting} +mov dword [dword fs:my_offset],0x11223344 +\end{lstlisting} + +Don't confuse the \code{DWORD} prefix \emph{outside} the square brackets, +which controls the size of the data stored at the address, with the +one \code{inside} the square brackets which controls the length of the +address itself. The two can quite easily be different: + +\begin{lstlisting} +mov word [dword 0x12345678],0x9ABC +\end{lstlisting} + +This moves 16 bits of data to an address specified by a 32-bit +offset. + +You can also specify \code{WORD} or \code{DWORD} prefixes along with the +\code{FAR} prefix to indirect far jumps or calls. For example: + +\begin{lstlisting} +call dword far [fs:word 0x4321] +\end{lstlisting} + +This instruction contains an address specified by a 16-bit offset; +it loads a 48-bit far pointer from that (16-bit segment and 32-bit +offset), and calls that address. + +\xsection{mixother}{Other Mixed-Size Instructions} + +The other way you might want to access data might be using the +string instructions (\code{LODSx}, \code{STOSx} and so on) or the +\code{XLATB} instruction. These instructions, since they take no +parameters, might seem to have no easy way to make them perform +32-bit addressing when assembled in a 16-bit segment. + +This is the purpose of NASM's \codeindex{a16}, \codeindex{a32} and +\codeindex{a64} prefixes. If you are coding \code{LODSB} in a 16-bit +segment but it is supposed to be accessing a string in a 32-bit segment, +you should load the desired address into \code{ESI} and then code + +\begin{lstlisting} +a32 lodsb +\end{lstlisting} + +The prefix forces the addressing size to 32 bits, meaning that +\code{LODSB} loads from \code{[DS:ESI]} instead of \code{[DS:SI]}. +To access a string in a 16-bit segment when coding in a 32-bit one, +the corresponding \code{a16} prefix can be used. + +The \code{a16}, \code{a32} and \code{a64} prefixes can be applied to +any instruction in NASM's instruction table, but most of them can +generate all the useful forms without them. The prefixes are necessary +only for instructions with implicit addressing: \code{CMPSx}, +\code{SCASx}, \code{LODSx}, \code{STOSx}, \code{MOVSx}, \code{INSx}, +\code{OUTSx}, and \code{XLATB}. Also, the various push and pop +instructions (\code{PUSHA} and \code{POPF} as well as the more usual +\code{PUSH} and \code{POP}) can accept \code{a16}, \code{a32} or +\code{a64} prefixes to force a particular one of \code{SP}, \code{ESP} or +\code{RSP} to be used as a stack pointer, in case the stack segment in +use is a different size from the code segment. + +\code{PUSH} and \code{POP}, when applied to segment registers in 32-bit +mode, also have the slightly odd behaviour that they push and pop 4 +bytes at a time, of which the top two are ignored and the bottom two +give the value of the segment register being manipulated. To force +the 16-bit behaviour of segment-register push and pop instructions, +you can use the operand-size prefix \codeindex{o16}: + +\begin{lstlisting} +o16 push ss +o16 push ds +\end{lstlisting} + +This code saves a doubleword of stack space by fitting two segment +registers into the space which would normally be consumed by pushing +one. + +(You can also use the \codeindex{o32} prefix to force the 32-bit behaviour +when in 16-bit mode, but this seems less useful.) diff --git a/doc/latex/src/nasm.tex b/doc/latex/src/nasm.tex new file mode 100644 index 00000000..6ba1920b --- /dev/null +++ b/doc/latex/src/nasm.tex @@ -0,0 +1,163 @@ +% +% vim: ts=4 sw=4 et +% +\documentclass[oneside,openany]{book} + +\usepackage[a4paper,margin=72pt]{geometry} + +\usepackage{listings} % nasm listings +\usepackage{imakeidx} % indexing +\usepackage{hyperref} % pdf bookmarks and such +\usepackage[Sonny]{fncychap} % chapter style +\usepackage{parskip} % no indent on first line +\usepackage{fontspec} % selecting fonts +\usepackage{xunicode} % unicode support +\usepackage{xcolor} % coloring +\usepackage{xspace} % spacing +\usepackage{appendix} % appendix +%\usepackage{xstring} % strings for code +\usepackage{sectsty} % colors for sections +\usepackage{graphicx} % images +\usepackage[titles]{tocloft} % coloring TOC + +\title{NASM -- The Netwide Assembler} +\author{The NASM Development Team} +\date{1996 -- 2018} +\input{src/version.tex} + +% +% No rectangles +\makeatletter +\hypersetup{ + pdfauthor=\@author, + pdftitle=\@title, + pdfkeywords={NASM,Netwide Assembler}, + hidelinks, +} +\makeatother + +% +% Up to 4 levels nesting in menu +\setcounter{tocdepth}{4} + +% +% Highlight listings +\definecolor{light-gray}{gray}{0.96} + +% +% Setup document fonts +\setmainfont{Source Sans Pro} +\setmonofont{FreeMono} + +% Listings font and settings +\newfontfamily{\lstsansserif}{FreeMono} +\lstset{ + keepspaces=true, + backgroundcolor=\color{light-gray}, + basicstyle=\lstsansserif, + breaklines=true, + breakatwhitespace=true, + framesep=10pt, + framexleftmargin=10pt, + frame=tb, + framerule=0pt, + xleftmargin=10pt, + xrightmargin=10pt, + aboveskip=10pt, + belowskip=5pt, + literate={-}{{-}}1 +} + +% +% Heading colors +\definecolor{hcolor}{RGB}{8,96,168} +\chapterfont{\color{hcolor}} +\sectionfont{\color{hcolor}} +\subsectionfont{\color{hcolor}} + +% +% Formatting macros +\newcommand{\textindex}[1]{#1\index{#1}\xspace} +\newcommand{\textindexlc}[1]{#1\index{\MakeLowercase{#1}}\xspace} +\newcommand{\code}[1]{{\texttt{#1}}\xspace} +\newcommand{\indexcode}[1]{\index{#1@\texttt{#1}}\xspace} +\newcommand{\codeindex}[1]{\texttt{#1}\index{#1@\texttt{#1}}\xspace} +\newcommand{\fullref}[1]{``\hyperref[{#1}]{\ref*{#1}\xspace\nameref*{#1}}''\xspace} +\newcommand{\nref}[1]{\textcolor{hcolor}{\hyperref[{#1}]{\ref*{#1}\xspace}}} + +\newcommand{\xchapter}[2]{\chapter{#2}\label{#1}\xspace} +\newcommand{\xsection}[2]{\section{#2}\label{#1}\xspace} +\newcommand{\xsubsection}[2]{\subsection{#2}\label{#1}\xspace} +% +% Convertion table +% +% \C{name} -> \xchapter{label}{name} +% \H{name} -> \xsection{label}{name} +% \S{name} -> \xsubsection{label}{name} +% \c{name} -> \code{name} +% \c name -> \begin{lstlisting} +% name +% \end{lstlisting} +% \i{name} -> \textindexlc{name} +% \I{name} -> \index{name} +% \I\c{name} -> \indexcode{name} +% \i\c{name} -> \codeindex{name} +% \k{name} -> \nref{name} + +% +% Index into TOC +\makeindex[title=Index,columns=2,intoc,options=-s src/idxconf.ist] + +% +% TOC headers +\renewcommand{\cftchapfont}{\bfseries\color{hcolor}} +\renewcommand{\cfttoctitlefont}{\huge\bfseries\color{hcolor}} + +\begin{document} +\raggedright + +\makeatletter +\begin{titlepage} + \color{hcolor} + \begin{center} \vspace*{\fill} + \begin{flushleft} + {\huge \bfseries {\@title}} \\ + \end{flushleft} + \noindent\makebox[\linewidth]{\rule{\textwidth}{2pt}} \\ + \begin{flushright} + {\large \bfseries \emph{version \version}} \\[8ex] + \end{flushright} + \includegraphics[width=6cm]{src/nasmlogo.eps} + \vspace*{\fill} \end{center} +\end{titlepage} +\makeatother +\thispagestyle{empty} + +\tableofcontents +\addtocontents{toc}{~\hfill\textcolor{hcolor}{\textbf{Page}}\par} + +% +% Document chapters +\input{src/intro.tex} +\input{src/running.tex} +\input{src/language.tex} +\input{src/preproc.tex} +\input{src/macropkg.tex} +\input{src/directive.tex} +\input{src/outfmt.tex} +\input{src/16bit.tex} +\input{src/32bit.tex} +\input{src/mixsize.tex} +\input{src/64bit.tex} +\input{src/trouble.tex} +\begin{appendices} +\input{src/ndisasm.tex} +\input{src/inslist.tex} +\input{src/changelog.tex} +\input{src/source.tex} +\input{src/contact.tex} +\end{appendices} + +\printindex + +\end{document} diff --git a/doc/latex/src/nasmlogo.eps b/doc/latex/src/nasmlogo.eps new file mode 100644 index 00000000..9ec29194 --- /dev/null +++ b/doc/latex/src/nasmlogo.eps @@ -0,0 +1,212 @@ +%!PS-Adobe-3.0 EPSF-3.0 +%%Creator: cairo 1.10.2 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+250.605 166.07 250.605 164.246 c 250.605 141.965 l 250.609 141.547 +250.52 141.172 250.336 140.832 c h +250.336 140.832 m f +Q Q +showpage +%%Trailer +count op_count sub {pop} repeat +countdictstack dict_count sub {end} repeat +cairo_eps_state restore +%%EOF diff --git a/doc/latex/src/ndisasm.tex b/doc/latex/src/ndisasm.tex new file mode 100644 index 00000000..d350a2c9 --- /dev/null +++ b/doc/latex/src/ndisasm.tex @@ -0,0 +1,174 @@ +% +% vim: ts=4 sw=4 et +% +\xchapter{ndisasm}{Ndisasm} + +The Netwide Disassembler, NDISASM. + +\xsection{ndisintro}{Introduction} + +The Netwide Disassembler is a small companion program to the Netwide +Assembler, NASM. It seemed a shame to have an x86 assembler, +complete with a full instruction table, and not make as much use of +it as possible, so here's a disassembler which shares the +instruction table (and some other bits of code) with NASM. + +The Netwide Disassembler does nothing except to produce +disassemblies of \emph{binary} source files. NDISASM does not have any +understanding of object file formats, like \code{objdump}, and it will +not understand \code{DOS .EXE} files like \code{debug} will. It just +disassembles. + +\xsection{ndisrun}{Running NDISASM} + +To disassemble a file, you will typically use a command of the form + +\begin{lstlisting} +ndisasm -b {16|32|64} filename +\end{lstlisting} + +NDISASM can disassemble 16-, 32- or 64-bit code equally easily, +provided of course that you remember to specify which it is to work +with. If no \codeindex{-b} switch is present, NDISASM works in 16-bit mode +by default. The \codeindex{-u} switch (for USE32) also invokes 32-bit mode. + +Two more command line options are \codeindex{-r} which reports the version +number of NDISASM you are running, and \codeindex{-h} which gives a short +summary of command line options. + +\xsubsection{ndiscom}{COM Files: Specifying an Origin} + +To disassemble a \code{DOS .COM} file correctly, a disassembler must +assume that the first instruction in the file is loaded at address +\code{0x100}, rather than at zero. NDISASM, which assumes by default +that any file you give it is loaded at zero, will therefore need +to be informed of this. + +The \codeindex{-o} option allows you to declare a different origin +for the file you are disassembling. Its argument may be expressed +in any of the NASM numeric formats: decimal by default, if it begins +with `\code{\$}' or `\code{0x}' or ends in `\code{H}' it's \code{hex}, +if it ends in `\code{Q}' it's \code{octal}, and if it ends in +`\code{B}' it's \code{binary}. + +Hence, to disassemble a \code{.COM} file: + +\begin{lstlisting} +ndisasm -o100h filename.com +\end{lstlisting} + +will do the trick. + +\xsubsection{ndissync}{Code Following Data: Synchronisation} + +Suppose you are disassembling a file which contains some data which +isn't machine code, and \emph{then} contains some machine code. NDISASM +will faithfully plough through the data section, producing machine +instructions wherever it can (although most of them will look +bizarre, and some may have unusual prefixes, e.g. `\code{FS OR AX,0x240A}'), +and generating `DB' instructions ever so often if it's totally stumped. +Then it will reach the code section. + +Supposing NDISASM has just finished generating a strange machine +instruction from part of the data section, and its file position is +now one byte \emph{before} the beginning of the code section. It's +entirely possible that another spurious instruction will get +generated, starting with the final byte of the data section, and +then the correct first instruction in the code section will not be +seen because the starting point skipped over it. This isn't really +ideal. + +To avoid this, you can specify a `\codeindex{synchronisation}' point, or indeed +as many synchronisation points as you like (although NDISASM can +only handle 2147483647 sync points internally). The definition of a sync +point is this: NDISASM guarantees to hit sync points exactly during +disassembly. If it is thinking about generating an instruction which +would cause it to jump over a sync point, it will discard that +instruction and output a `\code{db}' instead. So it \emph{will} start +disassembly exactly from the sync point, and so you \emph{will} see all +the instructions in your code section. + +Sync points are specified using the \codeindex{-s} option: they are measured +in terms of the program origin, not the file position. So if you +want to synchronize after 32 bytes of a \codeindex{.COM} file, you would have to +do + +\begin{lstlisting} +ndisasm -o100h -s120h file.com +\end{lstlisting} + +rather than + +\begin{lstlisting} +ndisasm -o100h -s20h file.com +\end{lstlisting} + +As stated above, you can specify multiple sync markers if you need +to, just by repeating the \code{-s} option. + + +\xsubsection{ndisisync}{Mixed Code and Data: Automatic (Intelligent) +Synchronisation} +\indexcode{auto-sync} + +Suppose you are disassembling the boot sector of a \code{DOS} floppy (maybe +it has a virus, and you need to understand the virus so that you +know what kinds of damage it might have done you). Typically, this +will contain a \code{JMP} instruction, then some data, then the rest of the +code. So there is a very good chance of NDISASM being \emph{misaligned} +when the data ends and the code begins. Hence a sync point is +needed. + +On the other hand, why should you have to specify the sync point +manually? What you'd do in order to find where the sync point would +be, surely, would be to read the \code{JMP} instruction, and then to use +its target address as a sync point. So can NDISASM do that for you? + +The answer, of course, is yes: using either of the synonymous +switches \codeindex{-a} (for automatic sync) or \codeindex{-i} +(for intelligent sync) will enable \code{auto-sync} mode. Auto-sync +mode automatically generates a sync point for any forward-referring +PC-relative jump or call instruction that NDISASM encounters. (Since +NDISASM is one-pass, if it encounters a PC-relative jump whose target +has already been processed, there isn't much it can do about it...) + +Only PC-relative jumps are processed, since an absolute jump is +either through a register (in which case NDISASM doesn't know what +the register contains) or involves a segment address (in which case +the target code isn't in the same segment that NDISASM is working +in, and so the sync point can't be placed anywhere useful). + +For some kinds of file, this mechanism will automatically put sync +points in all the right places, and save you from having to place +any sync points manually. However, it should be stressed that +auto-sync mode is \emph{not} guaranteed to catch all the sync points, and +you may still have to place some manually. + +Auto-sync mode doesn't prevent you from declaring manual sync +points: it just adds automatically generated ones to the ones you +provide. It's perfectly feasible to specify \code{-i} \emph{and} +some \code{-s} options. + +Another caveat with auto-sync mode is that if, by some unpleasant +fluke, something in your data section should disassemble to a +PC-relative call or jump instruction, NDISASM may obediently place a +sync point in a totally random place, for example in the middle of +one of the instructions in your code section. So you may end up with +a wrong disassembly even if you use auto-sync. Again, there isn't +much I can do about this. If you have problems, you'll have to use +manual sync points, or use the \code{-k} option (documented below) to +suppress disassembly of the data area. + +\xsubsection{ndisother}{Other Options} + +The \codeindex{-e} option skips a header on the file, by ignoring the first N +bytes. This means that the header is \emph{not} counted towards the +disassembly offset: if you give \code{-e10 -o10}, disassembly will start +at byte 10 in the file, and this will be given offset 10, not 20. + +The \codeindex{-k} option is provided with two comma-separated numeric +arguments, the first of which is an assembly offset and the second +is a number of bytes to skip. This \emph{will} count the skipped bytes +towards the assembly offset: its use is to suppress disassembly of a +data section which wouldn't contain anything you wanted to see +anyway. diff --git a/doc/latex/src/outfmt.tex b/doc/latex/src/outfmt.tex new file mode 100644 index 00000000..7f4cb976 --- /dev/null +++ b/doc/latex/src/outfmt.tex @@ -0,0 +1,1606 @@ +% +% vim: ts=4 sw=4 et +% +\xchapter{outfmt}{\textindexlc{Output Formats}} + +NASM is a portable assembler, designed to be able to compile on any +ANSI C-supporting platform and produce output to run on a variety of +Intel x86 operating systems. For this reason, it has a large number +of available output formats, selected using the \codeindex{-f} option +on the NASM \textindex{command line}. Each of these formats, along with +its extensions to the base NASM syntax, is detailed in this chapter. + +\xsection{binfmt}{\codeindex{bin}: \textindexlc{Flat-Form Binary}\index{pure binary} Output} +\index{file extension!bin} + +The \code{bin} format does not produce object files: it generates +nothing in the output file except the code you wrote. Such ``pure +binary'' files are used by \textindex{MS-DOS}: \codeindex{.COM} +executables and \codeindex{.SYS} device drivers are pure binary +files. Pure binary output is also useful for \textindex{operating system} +and \textindex{boot loader} development. + +The \code{bin} format supports \textindex{multiple section names}. +For details of how NASM handles sections in the \code{bin} format, +see \nref{multisec}. + +Using the \code{bin} format puts NASM by default into 16-bit mode +(see \nref{bits}). In order to use \code{bin} to write 32-bit +or 64-bit code, such as an OS kernel, you need to explicitly issue +the \indexcode{BITS}\code{BITS 32} or \indexcode{BITS}\code{BITS 64} +directive. + +\code{bin} has no default output file name extension: instead, it +leaves your file name as it is once the original extension has been +removed. Thus, the default is for NASM to assemble \code{binprog.asm} +into a binary file called \code{binprog}. + +\xsubsection{binorg}{\codeindex{ORG}: Binary File \textindexlc{Program Origin}} + +The \code{bin} format provides an additional directive to the list +given in \nref{directive}: \code{ORG}. The function of the +\code{ORG} directive is to specify the origin address which NASM +will assume the program begins at when it is loaded into memory. + +For example, the following code will generate the longword +\code{0x00000104}: + +\begin{lstlisting} +org 0x100 +dd label +label: +\end{lstlisting} + +Unlike the \code{ORG} directive provided by MASM-compatible assemblers, +which allows you to jump around in the object file and overwrite +code you have already generated, NASM's \code{ORG} does exactly what +the directive says: \emph{origin}. Its sole function is to specify one +offset which is added to all internal address references within the +section; it does not permit any of the trickery that MASM's version +does. See \nref{proborg} for further comments. + +\xsubsection{binseg}{\code{bin} Extensions to the \code{SECTION} Directive} +\index{section!bin extensions to} + +The \code{bin} output format extends the \code{SECTION} (or \code{SEGMENT}) +directive to allow you to specify the alignment requirements of segments. +This is done by appending the \codeindex{ALIGN} qualifier to the end of +the section-definition line. For example, + +\begin{lstlisting} +section .data align=16 +\end{lstlisting} + +switches to the section \code{.data} and also specifies that it must be +aligned on a 16-byte boundary. + +The parameter to \code{ALIGN} specifies how many low bits of the +section start address must be forced to zero. The alignment value +given may be any power of two. +\index{section alignment!in bin} +\index{segment alignment!in bin} +\index{alignment!in bin sections} + +\xsubsection{multisec}{\textindexlc{Multisection} Support for the \code{bin} Format} +\index{bin!multisection} + +The \code{bin} format allows the use of multiple sections, of arbitrary names, +besides the ``known'' \code{.text}, \code{.data}, and \code{.bss} names. + +\begin{itemize} + \item{Sections may be designated \codeindex{progbits} or \codeindex{nobits}. + Default is \code{progbits} (except \code{.bss}, which defaults to + \code{nobits}, of course).} + + \item{Sections can be aligned at a specified boundary following the previous + section with \code{align=}, or at an arbitrary byte-granular position with + \codeindex{start=}.} + + \item{Sections can be given a virtual start address, which will be used + for the calculation of all memory references within that section + with \codeindex{vstart=}.} + + \item{Sections can be ordered using \codeindex{follows=}\code{<section>} or + \codeindex{vfollows=}\code{<section>} as an alternative to specifying + an explicit start address.} + + \item{Arguments to \code{org}, \code{start}, \code{vstart}, and \code{align=} + are critical expressions. See \nref{crit}. E.g. + \code{align=(1 << ALIGN\_SHIFT)} - \code{ALIGN\_SHIFT} must be defined + before it is used here.} + + \item{Any code which comes before an explicit \code{SECTION} directive + is directed by default into the \code{.text} section.} + + \item{If an \code{ORG} statement is not given, \code{ORG 0} is used by default.} + + \item{The \code{.bss} section will be placed after the last \code{progbits} + section, unless \code{start=}, \code{vstart=}, \code{follows=}, or + \code{vfollows=} has been specified.} + + \item{All sections are aligned on dword boundaries, unless a different + alignment has been specified.} + + \item{Sections may not overlap.} + + \item{NASM creates the \code{section.<secname>.start} for each section, + which may be used in your code.} +\end{itemize} + +\xsubsection{map}{\textindexlc{Map Files}} +\index{file extension!map} + +Map files can be generated in \code{-f bin} format by means of the \code{[map]} +option. Map types of \code{all} (default), \code{brief}, \code{sections}, +\code{segments}, or \code{symbols} may be specified. Output may be directed +to \code{stdout} (default), \code{stderr}, or a specified file. E.g. +\code{[map symbols myfile.map]}. No ``user form'' exists, the square +brackets must be used. + +\xsection{ithfmt}{\codeindex{ith}: \textindexlc{Intel Hex} Output} +\index{file extension!ith} + +The \code{ith} file format produces Intel hex-format files. Just as the +\code{bin} format, this is a flat memory image format with no support for +relocation or linking. It is usually used with ROM programmers and +similar utilities. + +All extensions supported by the \code{bin} file format is also supported by +the \code{ith} file format. + +\code{ith} provides a default output file-name extension of \code{.ith}. + +\xsection{srecfmt}{\codeindex{srec}: \textindexlc{Motorola S-Records} Output} +\index{file extension!srec} + +The \code{srec} file format produces Motorola S-records files. Just as the +\code{bin} format, this is a flat memory image format with no support for +relocation or linking. It is usually used with ROM programmers and similar +utilities. + +All extensions supported by the \code{bin} file format is also supported by +the \code{srec} file format. + +\code{srec} provides a default output file-name extension of \code{.srec}. + +\xsection{objfmt}{\codeindex{obj}: \textindexlc{Microsoft OMF}\index{OMF} Object Files} +\index{file extension!obj} + +The \code{obj} file format (NASM calls it \code{obj} rather than +\code{omf} for historical reasons) is the one produced by \textindex{MASM} +and \textindex{TASM}, which is typically fed to 16-bit DOS linkers +to produce \codeindex{.EXE} files. It is also the format used by +\textindex{OS/2}. + +\code{obj} provides a default output file-name extension of \code{.obj}. + +\code{obj} is not exclusively a 16-bit format, though: NASM has full +support for the 32-bit extensions to the format. In particular, +32-bit \code{obj} format files are used by \textindex{Borland's Win32 +compilers}, instead of using Microsoft's newer \codeindex{win32} object +file format. + +The \code{obj} format does not define any special segment names: you +can call your segments anything you like. Typical names for segments +in \code{obj} format files are \code{CODE}, \code{DATA} and \code{BSS}. + +If your source file contains code before specifying an explicit +\code{SEGMENT} directive, then NASM will invent its own segment called +\codeindex{\_\_NASMDEFSEG} for you. + +When you define a segment in an \code{obj} file, NASM defines the +segment name as a symbol as well, so that you can access the segment +address of the segment. So, for example: + +\begin{lstlisting} +segment data + +dvar: dw 1234 + +segment code + +function: + mov ax,data ; get segment address of data + mov ds,ax ; and move it into DS + inc word [dvar] ; now this reference will work + ret +\end{lstlisting} + +The \code{obj} format also enables the use of the \codeindex{SEG} +and \codeindex{WRT} operators, so that you can write code which +does things like + +\begin{lstlisting} +extern foo + + mov ax,seg foo ; get preferred segment of foo + mov ds,ax + mov ax,data ; a different segment + mov es,ax + mov ax,[ds:foo] ; this accesses `foo' + mov [es:foo wrt data],bx ; so does this +\end{lstlisting} + +\xsubsection{objseg}{\code{obj} Extensions to the \code{SEGMENT} Directive} +\index{SEGMENT!obj extensions to} + +The \code{obj} output format extends the \code{SEGMENT} (or \code{SECTION}) +directive to allow you to specify various properties of the segment +you are defining. This is done by appending extra qualifiers to the +end of the segment-definition line. For example, + +\begin{lstlisting} +segment code private align=16 +\end{lstlisting} + +defines the segment \code{code}, but also declares it to be a private +segment, and requires that the portion of it described in this code +module must be aligned on a 16-byte boundary. + +The available qualifiers are: + +%\begin{tabular}{ l l } +%\codeindex{CLASS} & +%\begin{minipage}[t]{0.8\columnwidth} +%can be used to specify the segment class; this feature indicates to +%the linker that segments of the same class should be placed near each +%other in the output file. The class name can be any word, e.g. +%\code{CLASS=CODE}. +%\end{minipage} \\ +% +%\codeindex{OVERLAY} & +%\begin{minipage}[t]{0.8\columnwidth} +%like \code{CLASS}, is specified with an arbitrary word as an argument, +%and provides overlay information to an overlay-capable linker. +%\end{minipage} +%\end{tabular} + +\begin{itemize} + \item{\codeindex{PRIVATE}, \codeindex{PUBLIC}, \codeindex{COMMON} + and \codeindex{STACK} specify the combination characteristics + of the segment. \code{PRIVATE} segments do not get combined + with any others by the linker; \code{PUBLIC} and \code{STACK} + segments get concatenated together at link time; and \code{COMMON} + segments all get overlaid on top of each other rather than stuck + end-to-end.} + + \item{\codeindex{ALIGN} is used, as shown above, to specify how many + low bits of the segment start address must be forced to zero. + The alignment value given may be any power of two from 1 to 4096; + in reality, the only values supported are 1, 2, 4, 16, 256 and 4096, + so if 8 is specified it will be rounded up to 16, and 32, 64 and 128 + will all be rounded up to 256, and so on. Note that alignment to + 4096-byte boundaries is a \textindex{PharLap} extension to the + format and may not be supported by all linkers. + \index{section alignment!in OBJ} + \index{segment alignment!in OBJ} + \index{alignment!in OBJ sections}} + + \item{\codeindex{CLASS} can be used to specify the segment class; + this feature indicates to the linker that segments of the same + class should be placed near each other in the output file. + The class name can be any word, e.g. \code{CLASS=CODE}.} + + \item{\codeindex{OVERLAY}, like \code{CLASS}, is specified with + an arbitrary word as an argument, and provides overlay information + to an overlay-capable linker.} + + \item{Segments can be declared as \codeindex{USE16} or \codeindex{USE32}, + which has the effect of recording the choice in the object file + and also ensuring that NASM's default assembly mode when assembling + in that segment is 16-bit or 32-bit respectively.} + + \item{When writing \textindex{OS/2} object files, you should declare + 32-bit segments as \codeindex{FLAT}, which causes the default + segment base for anything in the segment to be the special group + \code{FLAT}, and also defines the group if it is not already defined.} + + \item{The \code{obj} file format also allows segments to be declared as + having a pre-defined absolute segment address, although no linkers + are currently known to make sensible use of this feature; + nevertheless, NASM allows you to declare a segment such as + \code{SEGMENT SCREEN ABSOLUTE=0xB800} if you need to. The + \codeindex{ABSOLUTE} and \code{ALIGN} keywords are mutually + exclusive.} +\end{itemize} + +NASM's default segment attributes are \code{PUBLIC}, \code{ALIGN=1}, no +class, no overlay, and \code{USE16}. + +\xsubsection{group}{\codeindex{GROUP}: Defining Groups of Segments} +\index{segments!groups of} + +The \code{obj} format also allows segments to be grouped, so that a +single segment register can be used to refer to all the segments in +a group. NASM therefore supplies the \code{GROUP} directive, whereby +you can code + +\begin{lstlisting} +segment data + ; some data +segment bss + ; some uninitialized data +group dgroup data bss +\end{lstlisting} + +which will define a group called \code{dgroup} to contain the segments +\code{data} and \code{bss}. Like \code{SEGMENT}, \code{GROUP} causes +the group name to be defined as a symbol, so that you can refer to +a variable \code{var} in the \code{data} segment as \code{var wrt data} +or as \code{var wrt dgroup}, depending on which segment value is +currently in your segment register. + +If you just refer to \code{var}, however, and \code{var} is declared +in a segment which is part of a group, then NASM will default to giving +you the offset of \code{var} from the beginning of the \emph{group}, +not the \emph{segment}. Therefore \code{SEG var}, also, will return +the group base rather than the segment base. + +NASM will allow a segment to be part of more than one group, but +will generate a warning if you do this. Variables declared in a +segment which is part of more than one group will default to being +relative to the first group that was defined to contain the segment. + +A group does not have to contain any segments; you can still make +\code{WRT} references to a group which does not contain the variable +you are referring to. OS/2, for example, defines the special group +\code{FLAT} with no segments in it. + +\xsubsection{uppercase}{\codeindex{UPPERCASE}: Disabling Case Sensitivity in Output} + +Although NASM itself is \textindex{case sensitive}, some OMF linkers are +not; therefore it can be useful for NASM to output single-case +object files. The \code{UPPERCASE} format-specific directive causes all +segment, group and symbol names that are written to the object file +to be forced to upper case just before being written. Within a +source file, NASM is still case-sensitive; but the object file can +be written entirely in upper case if desired. + +\code{UPPERCASE} is used alone on a line; it requires no parameters. + +\xsubsection{import}{\codeindex{IMPORT}: Importing DLL Symbols} +\index{DLL symbols!importing} +\index{symbols!importing from DLLs} + +The \code{IMPORT} format-specific directive defines a symbol to be +imported from a DLL, for use if you are writing a DLL's +\textindex{import library} in NASM. You still need to declare the +symbol as \code{EXTERN} as well as using the \code{IMPORT} +directive. + +The \code{IMPORT} directive takes two required parameters, separated +by white space, which are (respectively) the name of the symbol you +wish to import and the name of the library you wish to import it +from. For example: + +\begin{lstlisting} +import WSAStartup wsock32.dll +\end{lstlisting} + +A third optional parameter gives the name by which the symbol is +known in the library you are importing it from, in case this is not +the same as the name you wish the symbol to be known by to your code +once you have imported it. For example: + +\begin{lstlisting} +import asyncsel wsock32.dll WSAAsyncSelect +\end{lstlisting} + +\xsubsection{export}{\codeindex{EXPORT}: Exporting DLL Symbols} +\index{DLL symbols!exporting} +\index{symbols!exporting from DLLs} + +The \code{EXPORT} format-specific directive defines a global +symbol to be exported as a DLL symbol, for use if you are +writing a DLL in NASM. You still need to declare the symbol +as \code{GLOBAL} as well as using the \code{EXPORT} directive. + +\code{EXPORT} takes one required parameter, which is the name of the +symbol you wish to export, as it was defined in your source file. An +optional second parameter (separated by white space from the first) +gives the \emph{external} name of the symbol: the name by which you +wish the symbol to be known to programs using the DLL. If this name +is the same as the internal name, you may leave the second parameter +off. + +Further parameters can be given to define attributes of the exported +symbol. These parameters, like the second, are separated by white +space. If further parameters are given, the external name must also +be specified, even if it is the same as the internal name. The +available attributes are: + +\begin{itemize} + \item{\code{resident} indicates that the exported name is + to be kept resident by the system loader. This is + an optimisation for frequently used symbols imported + by name.} + + \item{\code{nodata} indicates that the exported symbol + is a function which does not make use of any initialized + data.} + + \item{\code{parm=NNN}, where \code{NNN} is an integer, sets + the number of parameter words for the case in which + the symbol is a call gate between 32-bit and 16-bit + segments.} + + \item{An attribute which is just a number indicates that + the symbol should be exported with an identifying + number (ordinal), and gives the desired number.} +\end{itemize} + +For example: + +\begin{lstlisting} +export myfunc +export myfunc TheRealMoreFormalLookingFunctionName +export myfunc myfunc 1234 ; export by ordinal +export myfunc myfunc resident parm=23 nodata +\end{lstlisting} + +\xsubsection{dotdotstart}{\codeindex{..start}: Defining the \textindexlc{Program Entry Point}} + +\code{OMF} linkers require exactly one of the object files being linked to +define the program entry point, where execution will begin when the +program is run. If the object file that defines the entry point is +assembled using NASM, you specify the entry point by declaring the +special symbol \code{..start} at the point where you wish execution to +begin. + +\xsubsection{objextern}{\code{obj} Extensions to the \code{EXTERN} Directive} +\index{EXTERN!obj extensions to} + +If you declare an external symbol with the directive + +\begin{lstlisting} +extern foo +\end{lstlisting} + +then references such as \code{mov ax,foo} will give you the offset of +\code{foo} from its preferred segment base (as specified in whichever +module \code{foo} is actually defined in). So to access the contents of +\code{foo} you will usually need to do something like + +\begin{lstlisting} +mov ax,seg foo ; get preferred segment base +mov es,ax ; move it into ES +mov ax,[es:foo] ; and use offset `foo' from it +\end{lstlisting} + +This is a little unwieldy, particularly if you know that an external +is going to be accessible from a given segment or group, say +\code{dgroup}. So if \code{DS} already contained \code{dgroup}, +you could simply code + +\begin{lstlisting} +mov ax,[foo wrt dgroup] +\end{lstlisting} + +However, having to type this every time you want to access \code{foo} +can be a pain; so NASM allows you to declare \code{foo} in the +alternative form + +\begin{lstlisting} +extern foo:wrt dgroup +\end{lstlisting} + +This form causes NASM to pretend that the preferred segment base of +\code{foo} is in fact \code{dgroup}; so the expression \code{seg foo} +will now return \code{dgroup}, and the expression \code{foo} is +equivalent to \code{foo wrt dgroup}. + +This \index{default-WRT mechanism}default-\code{WRT} mechanism can be used +to make externals appear to be relative to any group or segment in +your program. It can also be applied to common variables: see +\nref{objcommon}. + +\xsubsection{objcommon}{\code{obj} Extensions to the \code{COMMON} Directive} +\index{COMMON!obj extensions to} + +The \code{obj} format allows common variables to be either near +\index{common variables!near} or far\index{common variables!far}; +NASM allows you to specify which your variables should be by the +use of the syntax + +\begin{lstlisting} +common nearvar 2:near ; nearvar is a near common +common farvar 10:far ; and farvar is far +\end{lstlisting} + +Far common variables may be greater in size than 64Kb, and so the +OMF specification says that they are declared as a number of +\emph{elements} of a given size. So a 10-byte far common variable could +be declared as ten one-byte elements, five two-byte elements, two +five-byte elements or one ten-byte element. + +Some \code{OMF} linkers require the \index{element size!in common +variables}\index{common variables!element size}element size, as well as +the variable size, to match when resolving common variables declared +in more than one module. Therefore NASM must allow you to specify +the element size on your far common variables. This is done by the +following syntax: + +\begin{lstlisting} +common c_5by2 10:far 5 ; two five-byte elements +common c_2by5 10:far 2 ; five two-byte elements +\end{lstlisting} + +If no element size is specified, the default is 1. Also, the \code{FAR} +keyword is not required when an element size is specified, since +only far commons may have element sizes at all. So the above +declarations could equivalently be + +\begin{lstlisting} +common c_5by2 10:5 ; two five-byte elements +common c_2by5 10:2 ; five two-byte elements +\end{lstlisting} + +In addition to these extensions, the \code{COMMON} directive +in \code{obj} also supports default-\code{WRT} specification +like \code{EXTERN} does (explained in \nref{objextern}). +So you can also declare things like + +\begin{lstlisting} +common foo 10:wrt dgroup +common bar 16:far 2:wrt data +common baz 24:wrt data:6 +\end{lstlisting} + +\xsubsection{objdepend}{Embedded File Dependency Information} + +Since NASM 2.13.02, \code{obj} files contain embedded dependency file +information. To suppress the generation of dependencies, use + +\begin{lstlisting} +%pragma obj nodepend +\end{lstlisting} + +\xsection{win32fmt}{\codeindex{win32}: Microsoft Win32 Object Files} + +The \code{win32} output format generates Microsoft Win32 object files, +suitable for passing to Microsoft linkers such as \emph{Visual C++}. +Note that Borland Win32 compilers do not use this format, but use +\code{obj} instead (see \nref{objfmt}). + +\code{win32} provides a default output file-name extension of \code{.obj}. + +Note that although Microsoft say that Win32 object files follow the +COFF (Common Object File Format) standard, the object files produced +by Microsoft Win32 compilers are not compatible with COFF linkers such +as DJGPP's, and vice versa. This is due to a difference of opinion over +the precise semantics of PC-relative relocations. To produce COFF files +suitable for DJGPP, use NASM's \code{coff} output format; conversely, +the \code{coff} format does not produce object files that Win32 linkers +can generate correct output from. + +\xsubsection{win32sect}{\code{win32} Extensions to the \code{SECTION} Directive} +\index{SECTION!win32 extensions to} + +Like the \code{obj} format, \code{win32} allows you to specify additional +information on the \code{SECTION} directive line, to control the type +and properties of sections you declare. Section types and properties +are generated automatically by NASM for the \textindex{standard section names} +\code{.text}, \code{.data} and \code{.bss}, but may still be overridden by +these qualifiers. + +The available qualifiers are: + +\begin{itemize} + \item{\code{code}, or equivalently \code{text}, defines the section + to be a code section. This marks the section as readable and + executable, but not writable, and also indicates to the linker + that the type of the section is code.} + + \item{\code{data} and \code{bss} define the section to be a data + section, analogously to \code{code}. Data sections are marked + as readable and writable, but not executable. \code{data} + declares an initialized data section, whereas \code{bss} declares + an uninitialized data section.} + + \item{\code{rdata} declares an initialized data section that is + readable but not writable. Microsoft compilers use this section + to place constants in it.} + + \item{\code{info} defines the section to be an \textindex{informational section}, + which is not included in the executable file by the linker, but may + (for example) pass information \emph{to} the linker. For example, + declaring an \code{info}-type section called \codeindex{.drectve} causes + the linker to interpret the contents of the section as command-line + options.} + + \item{\code{align=}, used with a trailing number as in \code{obj}, gives the + \index{section alignment!in win32} \index{alignment!in win32 sections} + alignment requirements of the section. The maximum you may + specify is 64: the Win32 object file format contains no means to + request a greater section alignment than this. If alignment is not + explicitly specified, the defaults are 16-byte alignment for code + sections, 8-byte alignment for rdata sections and 4-byte alignment + for data (and BSS) sections. + Informational sections get a default alignment of 1 byte (no + alignment), though the value does not matter.} +\end{itemize} + +The defaults assumed by NASM if you do not specify the above +qualifiers are: + +\begin{lstlisting} +section .text code align=16 +section .data data align=4 +section .rdata rdata align=8 +section .bss bss align=4 +\end{lstlisting} + +Any other section name is treated by default like \code{.text}. + +\xsubsection{win32safeseh}{\code{win32} Safe Structured Exception Handling} + +Among other improvements in Windows XP SP2 and Windows Server 2003 +Microsoft has introduced concept of "safe structured exception +handling." General idea is to collect handlers' entry points in +designated read-only table and have alleged entry point verified +against this table prior exception control is passed to the handler. In +order for an executable module to be equipped with such "safe exception +handler table," all object modules on linker command line has to comply +with certain criteria. If one single module among them does not, then +the table in question is omitted and above mentioned run-time checks +will not be performed for application in question. Table omission is by +default silent and therefore can be easily overlooked. One can instruct +linker to refuse to produce binary without such table by passing +\code{/safeseh} command line option. + +Without regard to this run-time check merits it's natural to expect +NASM to be capable of generating modules suitable for \code{/safeseh} +linking. From developer's viewpoint the problem is two-fold: + +\begin{itemize} + \item{how to adapt modules not deploying exception handlers of their own;} + \item{how to adapt/develop modules utilizing custom exception handling.} +\end{itemize} + +Former can be easily achieved with any NASM version by adding following +line to source code: + +\begin{lstlisting} +$@feat.00 equ 1 +\end{lstlisting} + +As of version 2.03 NASM adds this absolute symbol automatically. If +it's not already present to be precise. I.e. if for whatever reason +developer would choose to assign another value in source file, it would +still be perfectly possible. + +Registering custom exception handler on the other hand requires certain +"magic." As of version 2.03 additional directive is implemented, +\code{safeseh}, which instructs the assembler to produce appropriately +formatted input data for above mentioned "safe exception handler +table." Its typical use would be: + +\begin{lstlisting} +section .text +extern _MessageBoxA@16 +%if __NASM_VERSION_ID__ >= 0x02030000 +safeseh handler ; register handler as "safe handler" +%endif +handler: + push DWORD 1 ; MB_OKCANCEL + push DWORD caption + push DWORD text + push DWORD 0 + call _MessageBoxA@16 + sub eax,1 ; incidentally suits as return value + ; for exception handler + ret +global _main +_main: + push DWORD handler + push DWORD [fs:0] + mov DWORD [fs:0],esp ; engage exception handler + xor eax,eax + mov eax,DWORD[eax] ; cause exception + pop DWORD [fs:0] ; disengage exception handler + add esp,4 + ret +text: db 'OK to rethrow, CANCEL to generate core dump',0 +caption:db 'SEGV',0 + +section .drectve info + db '/defaultlib:user32.lib /defaultlib:msvcrt.lib ' +\end{lstlisting} + +As you might imagine, it's perfectly possible to produce .exe binary +with "safe exception handler table" and yet engage unregistered +exception handler. Indeed, handler is engaged by simply manipulating +\code{[fs:0]} location at run-time, something linker has no power over, +run-time that is. It should be explicitly mentioned that such failure +to register handler's entry point with \code{safeseh} directive has +undesired side effect at run-time. If exception is raised and +unregistered handler is to be executed, the application is abruptly +terminated without any notification whatsoever. One can argue that +system could at least have logged some kind "non-safe exception +handler in x.exe at address n" message in event log, but no, literally +no notification is provided and user is left with no clue on what +caused application failure. + +Finally, all mentions of linker in this paragraph refer to Microsoft +linker version 7.x and later. Presence of \code{@feat.00} symbol and input +data for "safe exception handler table" causes no backward +incompatibilities and "safeseh" modules generated by NASM 2.03 and +later can still be linked by earlier versions or non-Microsoft linkers. + +\xsubsection{codeview}{Debugging formats for Windows} +\index{Windows debugging formats} + +The \code{win32} and \code{win64} formats support the Microsoft CodeView +debugging format. Currently CodeView version 8 format is supported +(\codeindex{cv8}), but newer versions of the CodeView debugger should be +able to handle this format as well. + +\xsection{win64fmt}{\codeindex{win64}: Microsoft Win64 Object Files} + +The \code{win64} output format generates Microsoft Win64 object files, +which is nearly 100\% identical to the \code{win32} object format +(\nref{win32fmt}) with the exception that it is meant to target +64-bit code and the x86-64 platform altogether. This object file is used +exactly the same as the \code{win32} object format, in NASM, with regard to this exception. + +\xsubsection{win64pic}{\code{win64}: Writing Position-Independent Code} + +While \code{REL} takes good care of RIP-relative addressing, there is one +aspect that is easy to overlook for a Win64 programmer: indirect +references. Consider a switch dispatch table: + +\begin{lstlisting} + jmp qword [dsptch+rax*8] + ... +dsptch: dq case0 + dq case1 + ... +\end{lstlisting} + +Even a novice Win64 assembler programmer will soon realize that the code +is not 64-bit savvy. Most notably linker will refuse to link it with + +\begin{lstlisting} +'ADDR32' relocation to '.text' invalid without /LARGEADDRESSAWARE:NO +\end{lstlisting} + +So [s]he will have to split jmp instruction as following: + +\begin{lstlisting} + lea rbx,[rel dsptch] + jmp qword [rbx+rax*8] +\end{lstlisting} + +What happens behind the scene is that effective address in \code{lea} is +encoded relative to instruction pointer, or in perfectly position-independent +manner. But this is only part of the problem! Trouble is that in .dll context +\code{caseN} relocations will make their way to the final module and might +have to be adjusted at .dll load time. To be specific when it can't be loaded +at preferred address. And when this occurs, pages with such relocations will +be rendered private to current process, which kind of undermines the idea +of sharing .dll. But no worry, it's trivial to fix: + +\begin{lstlisting} + lea rbx,[rel dsptch] + add rbx,[rbx+rax*8] + jmp rbx + ... +dsptch: dq case0-dsptch + dq case1-dsptch + ... +\end{lstlisting} + +NASM version 2.03 and later provides another alternative, \code{wrt +..imagebase} operator, which returns offset from base address of the +current image, be it .exe or .dll module, therefore the name. For those +acquainted with PE-COFF format base address denotes start of +\code{IMAGE\_DOS\_HEADER} structure. Here is how to implement switch with +these image-relative references: + +\begin{lstlisting} + lea rbx,[rel dsptch] + mov eax,[rbx+rax*4] + sub rbx,dsptch wrt ..imagebase + add rbx,rax + jmp rbx + ... +dsptch: dd case0 wrt ..imagebase + dd case1 wrt ..imagebase +\end{lstlisting} + +One can argue that the operator is redundant. Indeed, snippet before +last works just fine with any NASM version and is not even Windows +specific... The real reason for implementing \code{wrt ..imagebase} will +become apparent in next paragraph. + +It should be noted that \code{wrt ..imagebase} is defined as 32-bit +operand only: + +\begin{lstlisting} +dd label wrt ..imagebase ; ok +dq label wrt ..imagebase ; bad +mov eax,label wrt ..imagebase ; ok +mov rax,label wrt ..imagebase ; bad +\end{lstlisting} + +\xsubsection{win64seh}{\code{win64}: Structured Exception Handling} + +Structured exception handing in Win64 is completely different matter +from Win32. Upon exception program counter value is noted, and +linker-generated table comprising start and end addresses of all the +functions [in given executable module] is traversed and compared to the +saved program counter. Thus so called \code{UNWIND\_INFO} structure is +identified. If it's not found, then offending subroutine is assumed to +be "leaf" and just mentioned lookup procedure is attempted for its +caller. In Win64 leaf function is such function that does not call any +other function \emph{nor} modifies any Win64 non-volatile registers, +including stack pointer. The latter ensures that it's possible to +identify leaf function's caller by simply pulling the value from the +top of the stack. + +While majority of subroutines written in assembler are not calling any +other function, requirement for non-volatile registers' immutability +leaves developer with not more than 7 registers and no stack frame, +which is not necessarily what [s]he counted with. Customarily one would +meet the requirement by saving non-volatile registers on stack and +restoring them upon return, so what can go wrong? If [and only if] an +exception is raised at run-time and no \code{UNWIND\_INFO} structure is +associated with such "leaf" function, the stack unwind procedure will +expect to find caller's return address on the top of stack immediately +followed by its frame. Given that developer pushed caller's +non-volatile registers on stack, would the value on top point at some +code segment or even addressable space? Well, developer can attempt +copying caller's return address to the top of stack and this would +actually work in some very specific circumstances. But unless developer +can guarantee that these circumstances are always met, it's more +appropriate to assume worst case scenario, i.e. stack unwind procedure +going berserk. Relevant question is what happens then? Application is +abruptly terminated without any notification whatsoever. Just like in +Win32 case, one can argue that system could at least have logged +"unwind procedure went berserk in x.exe at address n" in event log, but +no, no trace of failure is left. + +Now, when we understand significance of the \code{UNWIND\_INFO} structure, +let's discuss what's in it and/or how it's processed. First of all it +is checked for presence of reference to custom language-specific +exception handler. If there is one, then it's invoked. Depending on the +return value, execution flow is resumed (exception is said to be +"handled"), \emph{or} rest of \code{UNWIND\_INFO} structure is processed as +following. Beside optional reference to custom handler, it carries +information about current callee's stack frame and where non-volatile +registers are saved. Information is detailed enough to be able to +reconstruct contents of caller's non-volatile registers upon call to +current callee. And so caller's context is reconstructed, and then +unwind procedure is repeated, i.e. another \code{UNWIND\_INFO} structure is +associated, this time, with caller's instruction pointer, which is then +checked for presence of reference to language-specific handler, etc. +The procedure is recursively repeated till exception is handled. As +last resort system "handles" it by generating memory core dump and +terminating the application. + +As for the moment of this writing NASM unfortunately does not +facilitate generation of above mentioned detailed information about +stack frame layout. But as of version 2.03 it implements building +blocks for generating structures involved in stack unwinding. As +simplest example, here is how to deploy custom exception handler for +leaf function: + +\begin{lstlisting} +default rel +section .text +extern MessageBoxA +handler: + sub rsp,40 + mov rcx,0 + lea rdx,[text] + lea r8,[caption] + mov r9,1 ; MB_OKCANCEL + call MessageBoxA + sub eax,1 ; incidentally suits as return value + ; for exception handler + add rsp,40 + ret +global main +main: + xor rax,rax + mov rax,QWORD[rax] ; cause exception + ret +main_end: +text: db 'OK to rethrow, CANCEL to generate core dump',0 +caption:db 'SEGV',0 + +section .pdata rdata align=4 + dd main wrt ..imagebase + dd main_end wrt ..imagebase + dd xmain wrt ..imagebase +section .xdata rdata align=8 +xmain: db 9,0,0,0 + dd handler wrt ..imagebase +section .drectve info + db '/defaultlib:user32.lib /defaultlib:msvcrt.lib ' +\end{lstlisting} + +What you see in \code{.pdata} section is element of the "table comprising +start and end addresses of function" along with reference to associated +\code{UNWIND\_INFO} structure. And what you see in \code{.xdata} section is +\code{UNWIND\_INFO} structure describing function with no frame, but with +designated exception handler. References are \emph{required} to be +image-relative (which is the real reason for implementing \code{wrt +..imagebase} operator). It should be noted that \code{rdata align=n}, as +well as \code{wrt ..imagebase}, are optional in these two segments' +contexts, i.e. can be omitted. Latter means that \emph{all} 32-bit +references, not only above listed required ones, placed into these two +segments turn out image-relative. Why is it important to understand? +Developer is allowed to append handler-specific data to \code{UNWIND\_INFO} +structure, and if [s]he adds a 32-bit reference, then [s]he will have +to remember to adjust its value to obtain the real pointer. + +As already mentioned, in Win64 terms leaf function is one that does not +call any other function \emph{nor} modifies any non-volatile register, +including stack pointer. But it's not uncommon that assembler +programmer plans to utilize every single register and sometimes even +have variable stack frame. Is there anything one can do with bare +building blocks? I.e. besides manually composing fully-fledged +\code{UNWIND\_INFO} structure, which would surely be considered +error-prone? Yes, there is. Recall that exception handler is called +first, before stack layout is analyzed. As it turned out, it's +perfectly possible to manipulate current callee's context in custom +handler in manner that permits further stack unwinding. General idea is +that handler would not actually "handle" the exception, but instead +restore callee's context, as it was at its entry point and thus mimic +leaf function. In other words, handler would simply undertake part of +unwinding procedure. Consider following example: + +\begin{lstlisting} +function: + mov rax,rsp ; copy rsp to volatile register + push r15 ; save non-volatile registers + push rbx + push rbp + mov r11,rsp ; prepare variable stack frame + sub r11,rcx + and r11,-64 + mov QWORD[r11],rax ; check for exceptions + mov rsp,r11 ; allocate stack frame + mov QWORD[rsp],rax ; save original rsp value +magic_point: + ... + mov r11,QWORD[rsp] ; pull original rsp value + mov rbp,QWORD[r11-24] + mov rbx,QWORD[r11-16] + mov r15,QWORD[r11-8] + mov rsp,r11 ; destroy frame + ret +\end{lstlisting} + +The keyword is that up to \code{magic\_point} original \code{rsp} value +remains in chosen volatile register and no non-volatile register, +except for \code{rsp}, is modified. While past \code{magic\_point} +\code{rsp} remains constant till the very end of the \code{function}. +In this case custom language-specific exception handler would look like this: + +\begin{lstlisting} +EXCEPTION_DISPOSITION +handler(EXCEPTION_RECORD *rec, ULONG64 frame, + CONTEXT *context, DISPATCHER_CONTEXT *disp) +{ + ULONG64 *rsp; + + if (context->Rip < (ULONG64)magic_point) + rsp = (ULONG64 *)context->Rax; + else { + rsp = ((ULONG64 **)context->Rsp)[0]; + context->Rbp = rsp[-3]; + context->Rbx = rsp[-2]; + context->R15 = rsp[-1]; + } + context->Rsp = (ULONG64)rsp; + + memcpy(disp->ContextRecord, context, sizeof(CONTEXT)); + RtlVirtualUnwind(UNW_FLAG_NHANDLER, disp->ImageBase, + dips->ControlPc, disp->FunctionEntry, + disp->ContextRecord, + &disp->HandlerData, + &disp->EstablisherFrame, + NULL); + + return ExceptionContinueSearch; +} +\end{lstlisting} + +As custom handler mimics leaf function, corresponding \code{UNWIND\_INFO} +structure does not have to contain any information about stack frame +and its layout. + +\xsection{cofffmt}{\codeindex{coff}: \textindexlc{Common Object File Format}} + +The \code{coff} output type produces \code{COFF} object files suitable for +linking with the \textindex{DJGPP} linker. + +\code{coff} provides a default output file-name extension of \code{.o}. + +The \code{coff} format supports the same extensions to the \code{SECTION} +directive as \code{win32} does, except that the \code{align} qualifier and +the \code{info} section type are not supported. + +\xsection{machofmt}{\codeindex{macho32} and \codeindex{macho64}: +\textindexlc{Mach Object File Format}} +\index{Mach-O} + +The \code{macho32}, \code{macho64} output formts produces Mach-O +object files suitable for linking with the \textindex{MacOS X} linker. +\codeindex{macho} is a synonym for \code{macho32}. + +\code{macho} provides a default output file-name extension of \code{.o}. + +\xsubsection{machosect}{\code{macho} extensions to the \code{SECTION} Directive} +\index{SECTION!macho extensions to} + +The \code{macho} output format specifies section names in the format +"\emph{segment}\code{,}\emph{section}". No spaces are allowed around the +comma. The following flags can also be specified: + +\begin{itemize} + \item{\code{data} - this section contains initialized data items} + \item{\code{code} - this section contains code exclusively} + \item{\code{mixed} - this section contains both code and data} + \item{\code{bss} - this section is uninitialized and filled with zero} + \item{\code{zerofill} - same as \code{bss}} + \item{\code{no\_dead\_strip} - inhibit dead code stripping for this section} + \item{\code{live\_support} - set the live support flag for this section} + \item{\code{strip\_static\_syms} - strip static symbols for this section} + \item{\code{debug} - this section contains debugging information} + \item{\code{align=}\emph{alignment} - specify section alignment} +\end{itemize} + +The default is \code{data}, unless the section name is \code{\_\_text} or +\code{\_\_bss} in which case the default is \code{text} or \code{bss}, +respectively. + +For compatibility with other Unix platforms, the following standard +names are also supported: + +\begin{lstlisting} +.text = __TEXT,__text text +.rodata = __DATA,__const data +.data = __DATA,__data data +.bss = __DATA,__bss bss +\end{lstlisting} + +If the \code{.rodata} section contains no relocations, it is instead put +into the \code{\_\_TEXT,\_\_const} section unless this section has already +been specified explicitly. However, it is probably better to specify +\code{\_\_TEXT,\_\_const} and \code{\_\_DATA,\_\_const} explicitly as appropriate. + +\xsubsection{machotls}{\textindexlc{Thread Local Storage in Mach-O}\index{TLS}: +\code{macho} special symbols and \codeindex{WRT}} + +Mach-O defines the following special symbols that can be used on the +right-hand side of the \code{WRT} operator: + +\begin{itemize} + \item{\code{..tlvp} is used to specify access to thread-local storage.} + \item{\code{..gotpcrel} is used to specify references to the Global Offset Table. + The GOT is supported in the \code{macho64} format only.} +\end{itemize} + +\xsubsection{macho-ssvs}{\code{macho} specfic directive +\codeindex{subsections\_via\_symbols}} + +The directive \code{subsections\_via\_symbols} sets the +\code{MH\_SUBSECTIONS\_VIA\_SYMBOLS} flag in the Mach-O header, +that effectively separates a block (or a subsection) based on a symbol. +It is often used for eliminating dead codes by a linker. + +This directive takes no arguments. + +This is a macro implemented as a \code{\%pragma}. It can also be +specified in its \code{\%pragma} form, in which case it will not affect +non-Mach-O builds of the same source code: + +\begin{lstlisting} +%pragma macho subsections_via_symbols +\end{lstlisting} + +\xsubsection{macho-snds}{\code{macho} specfic directive \codeindex{no\_dead\_strip}} + +The directive \code{no\_dead\_strip} sets the Mach-O \code{SH\_NO\_DEAD\_STRIP} +section flag on the section containing a a specific symbol. This directive takes +a list of symbols as its arguments. + +This is a macro implemented as a \code{\%pragma}. It can also be +specified in its \code{\%pragma} form, in which case it will not affect +non-Mach-O builds of the same source code: + +\begin{lstlisting} +%pragma macho no_dead_strip symbol... +\end{lstlisting} + +\xsubsection{macho-pext}{\code{macho} specific extensions to the +\code{GLOBAL} Directive: \codeindex{private\_extern}} + +The directive extension to \code{GLOBAL} marks the symbol with limited +global scope. For example, you can specify the global symbol with +this extension: + +\begin{lstlisting} +global foo:private_extern +foo: + ; codes +\end{lstlisting} + +Using with static linker will clear the private extern attribute. +But linker option like \code{-keep\_private\_externs} can avoid it. + +\xsection{elffmt}{\codeindex{elf32}, \codeindex{elf64}, \codeindex{elfx32}: +\textindexlc{Executable and Linkable Format} Object Files} +\index{ELF}\index{linux!elf} + +The \code{elf32}, \code{elf64} and \code{elfx32} output formats generate +\code{ELF32} and \code{ELF64} (Executable and Linkable Format) object files, +as used by Linux as well as \textindex{Unix System V}, including +\textindex{Solaris x86}, \textindex{UnixWare} and \textindex{SCO Unix}. +\code{elf} provides a default output file-name extension of \code{.o}. +\code{elf} is a synonym for \code{elf32}. + +The \code{elfx32} format is used for the \textindex{x32} ABI, which is +a 32-bit ABI with the CPU in 64-bit mode. + +\xsubsection{abisect}{ELF specific directive \codeindex{osabi}} + +The ELF header specifies the application binary interface for the +target operating system (OSABI). This field can be set by using the +\code{osabi} directive with the numeric value (0-255) of the target +system. If this directive is not used, the default value will be "UNIX +System V ABI" (0) which will work on most systems which support ELF. + +\xsubsection{elfsect}{\code{elf} extensions to the \code{SECTION} Directive} +\index{SECTION!elf extensions to} + +Like the \code{obj} format, \code{elf} allows you to specify additional +information on the \code{SECTION} directive line, to control the type +and properties of sections you declare. Section types and properties +are generated automatically by NASM for the \textindexlc{standard section +names}, but may still be overridden by these qualifiers. + +The available qualifiers are: + +\begin{itemize} + \item{\codeindex{alloc} defines the section to be one which is loaded into + memory when the program is run. \codeindex{noalloc} defines it to be one + which is not, such as an informational or comment section.} + + \item{\codeindex{exec} defines the section to be one which should have execute + permission when the program is run. \codeindex{noexec} defines it as one + which should not.} + + \item{\codeindex{write} defines the section to be one which should be writable + when the program is run. \codeindex{nowrite} defines it as one which should + not.} + + \item{\codeindex{progbits} defines the section to be one with explicit contents + stored in the object file: an ordinary code or data section, for + example, \codeindex{nobits} defines the section to be one with no explicit + contents given, such as a BSS section.} + + \item{\code{align=}, used with a trailing number as in \code{obj}, gives the + \index{section alignment!in elf}\index{alignment!in elf sections}alignment + requirements of the section.} + + \item{\codeindex{tls} defines the section to be one which contains + thread local variables.} +\end{itemize} + +The defaults assumed by NASM if you do not specify the above +qualifiers are: +\indexcode{.text} \indexcode{.rodata} \indexcode{.lrodata} +\indexcode{.data} \indexcode{.ldata} \indexcode{.bss} +\indexcode{.lbss} \indexcode{.tdata} \indexcode{.tbss} +\indexcode{.comment} + +\begin{lstlisting} +section .text progbits alloc exec nowrite align=16 +section .rodata progbits alloc noexec nowrite align=4 +section .lrodata progbits alloc noexec nowrite align=4 +section .data progbits alloc noexec write align=4 +section .ldata progbits alloc noexec write align=4 +section .bss nobits alloc noexec write align=4 +section .lbss nobits alloc noexec write align=4 +section .tdata progbits alloc noexec write align=4 tls +section .tbss nobits alloc noexec write align=4 tls +section .comment progbits noalloc noexec nowrite align=1 +section other progbits alloc noexec nowrite align=1 +\end{lstlisting} + +(Any section name other than those in the above table is treated by +default like \code{other} in the above. Please note that section +names are case sensitive.) + +\xsubsection{elfwrt}{\textindexlc{Position-Independent Code}: \code{elf} +Special Symbols and \codeindex{WRT}} +\index{PIC} + +Since \code{ELF} does not support segment-base references, the \code{WRT} +operator is not used for its normal purpose; therefore NASM's \code{elf} +output format makes use of \code{WRT} for a different purpose, namely the +PIC-specific \index{relocations!PIC-specific}relocation types. + +\code{elf} defines five special symbols which you can use as the +right-hand side of the \code{WRT} operator to obtain PIC relocation +types. They are \codeindex{..gotpc}, \codeindex{..gotoff}, \codeindex{..got}, +\codeindex{..plt} and \codeindex{..sym}. Their functions are summarized here: + +\begin{itemize} + \item{Referring to the symbol marking the global offset table base + using \code{wrt ..gotpc} will end up giving the distance from the + beginning of the current section to the global offset table. + (\codeindex{\_GLOBAL\_OFFSET\_TABLE\_} is the standard symbol name + used to refer to the \textindex{GOT}.) So you would then need to add + \codeindex{\$\$} to the result to get the real address of the GOT.} + + \item{Referring to a location in one of your own sections using + \code{wrt ..gotoff} will give the distance from the beginning of + the GOT to the specified location, so that adding on the address + of the GOT would give the real address of the location you wanted.} + + \item{Referring to an external or global symbol using \code{wrt ..got} + causes the linker to build an entry \emph{in} the GOT containing the + address of the symbol, and the reference gives the distance from the + beginning of the GOT to the entry; so you can add on the address of + the GOT, load from the resulting address, and end up with the + address of the symbol.} + + \item{Referring to a procedure name using \code{wrt ..plt} causes the + linker to build a \textindex{procedure linkage table} entry for the symbol, + and the reference gives the address of the \textindex{PLT} entry. You can + only use this in contexts which would generate a PC-relative + relocation normally (i.e. as the destination for \code{CALL} or + \code{JMP}), since ELF contains no relocation type to refer to PLT + entries absolutely.} + + \item{Referring to a symbol name using \code{wrt ..sym} causes NASM to + write an ordinary relocation, but instead of making the relocation + relative to the start of the section and then adding on the offset + to the symbol, it will write a relocation record aimed directly at + the symbol in question. The distinction is a necessary one due to a + peculiarity of the dynamic linker.} +\end{itemize} + +A fuller explanation of how to use these relocation types to write +shared libraries entirely in NASM is given in \nref{picdll}. + +\xsubsection{elftls}{\textindexlc{Thread Local Storage in ELF}: +\code{elf} Special Symbols and \codeindex{WRT}} +\index{TLS} + +In ELF32 mode, referring to an external or global symbol using +\code{wrt ..tlsie}\indexcode{..tlsie} causes the linker to build +an entry \emph{in} the GOT containing the +offset of the symbol within the TLS block, so you can access the value +of the symbol with code such as: + +\begin{lstlisting} +mov eax,[tid wrt ..tlsie] +mov [gs:eax],ebx +\end{lstlisting} + +In ELF64 or ELFx32 mode, referring to an external or global symbol using +\code{wrt ..gottpoff}\indexcode{..gottpoff} causes the linker to build an +entry \emph{in} the GOT containing the offset of the symbol within the TLS +block, so you can access the value of the symbol with code such as: + +\begin{lstlisting} +mov rax,[rel tid wrt ..gottpoff] +mov rcx,[fs:rax] +\end{lstlisting} + +\xsubsection{elfglob}{\code{elf} Extensions to the \code{GLOBAL} Directive} +\index{GLOBAL!elf extensions to} + +\code{ELF} object files can contain more information about a global symbol +than just its address: they can contain the \index{symbol sizes!specifying} +\index{size!of symbols}size of the symbol and its \index{symbol types!specifying} +\index{type!of symbols}type as well. These are not merely debugger conveniences, +but are actually necessary when the program being written is a +\textindexlc{shared library}. NASM therefore supports some extensions to the +\code{GLOBAL} directive, allowing you to specify these features. + +You can specify whether a global variable is a function or a data +object by suffixing the name with a colon and the word +\codeindex{function} or \codeindex{data}. (\codeindex{object} is +a synonym for \code{data}.) For example: + +\begin{lstlisting} +global hashlookup:function, hashtable:data +\end{lstlisting} + +exports the global symbol \code{hashlookup} as a function and +\code{hashtable} as a data object. + +Optionally, you can control the ELF visibility of the symbol. Just +add one of the visibility keywords: \codeindex{default}, +\codeindex{internal}, \codeindex{hidden}, or \codeindex{protected}. +The default is \code{default} of course. For example, to make +\code{hashlookup} hidden: + +\begin{lstlisting} +global hashlookup:function hidden +\end{lstlisting} + +You can also specify the size of the data associated with the +symbol, as a numeric expression (which may involve labels, and even +forward references) after the type specifier. Like this: + +\begin{lstlisting} +global hashtable:data (hashtable.end - hashtable) + +hashtable: + db this,that,theother ; some data here +.end: +\end{lstlisting} + +This makes NASM automatically calculate the length of the table and +place that information into the \code{ELF} symbol table. + +Declaring the type and size of global symbols is necessary when +writing shared library code. For more information, see +\nref{picglobal}. + +\xsubsection{elfcomm}{\code{elf} Extensions to the \code{COMMON} Directive} +\index{COMMON!elf extensions to} + +\code{ELF} also allows you to specify alignment requirements +\index{common variables!alignment in elf} +\index{alignment!of elf common variables} on common variables. +This is done by putting a number (which must be a power of two) +after the name and size of the common variable, separated (as usual) +by a colon. For example, an array of doublewords would benefit from +4-byte alignment: + +\begin{lstlisting} +common dwordarray 128:4 +\end{lstlisting} + +This declares the total size of the array to be 128 bytes, and +requires that it be aligned on a 4-byte boundary. + +\xsubsection{elf16}{16-bit code and ELF} +\index{ELF!16-bit code and} + +The \code{ELF32} specification doesn't provide relocations for 8- and +16-bit values, but the GNU \code{ld} linker adds these as an extension. +NASM can generate GNU-compatible relocations, to allow 16-bit code to +be linked as ELF using GNU \code{ld}. If NASM is used with the +\code{-w+gnu-elf-extensions} option, a warning is issued when one of +these relocations is generated. + +\xsubsection{elfdbg}{Debug formats and ELF} +\index{ELF!Debug formats} + +ELF provides debug information in \code{STABS} and \code{DWARF} formats. +Line number information is generated for all executable sections, but please +note that only the ".text" section is executable by default. + +\xsection{aoutfmt}{\codeindex{aout}: Linux \code{a.out} Object Files} +\index{a.out!Linux version} +\index{linux!a.out} + +The \code{aout} format generates \code{a.out} object files, in the +form used by early Linux systems (current Linux systems use ELF, see +\nref{elffmt}.) These differ from other \code{a.out} object +files in that the magic number in the first four bytes of the file is +different; also, some implementations of \code{a.out}, for example +NetBSD's, support position-independent code, which Linux's +implementation does not. + +\code{a.out} provides a default output file-name extension of \code{.o}. + +\code{a.out} is a very simple object format. It supports no special +directives, no special symbols, no use of \code{SEG} or \code{WRT}, and no +extensions to any standard directives. It supports only the three +\textindexlc{standard section names} \codeindex{.text}, \codeindex{.data} +and \codeindex{.bss}. + +\xsection{aoutbfmt}{\codeindex{aoutb}: \textindex{NetBSD}/\textindex{FreeBSD}/\textindex{OpenBSD} +\code{a.out} Object Files} +\index{a.out!BSD version} + +The \code{aoutb} format generates \code{a.out} object files, in the form +used by the various free \code{BSD Unix} clones, \code{NetBSD}, \code{FreeBSD} +and \code{OpenBSD}. For simple object files, this object format is exactly +the same as \code{aout} except for the magic number in the first four bytes +of the file. However, the \code{aoutb} format supports +\index{PIC}\textindexlc{position-independent code} in the same way as the +\code{elf} format, so you can use it to write \code{BSD} +\textindexlc{shared libraries}. + +\code{aoutb} provides a default output file-name extension of \code{.o}. + +\code{aoutb} supports no special directives, no special symbols, and +only the three \textindexlc{standard section names} \codeindex{.text}, +\codeindex{.data} and \codeindex{.bss}. However, it also supports the same +use of \codeindex{WRT} as \code{elf} does, to provide position-independent +code relocation types. See \nref{elfwrt} for full documentation +of this feature. + +\code{aoutb} also supports the same extensions to the \code{GLOBAL} +directive as \code{elf} does: see \nref{elfglob} for +documentation of this. + +\xsection{as86fmt}{\code{as86}: \textindex{Minix}/Linux \codeindex{as86} Object Files} +\index{linux!as86} + +The Minix/Linux 16-bit assembler \code{as86} has its own non-standard +object file format. Although its companion linker \codeindex{ld86} +produces something close to ordinary \code{a.out} binaries as output, +the object file format used to communicate between \code{as86} and +\code{ld86} is not itself \code{a.out}. + +NASM supports this format, just in case it is useful, as \code{as86}. +\code{as86} provides a default output file-name extension of \code{.o}. + +\code{as86} is a very simple object format (from the NASM user's point +of view). It supports no special directives, no use of \code{SEG} or +\code{WRT}, and no extensions to any standard directives. It supports +only the three \textindexlc{standard section names} \codeindex{.text}, +\codeindex{.data} and \codeindex{.bss}. The only special symbol supported +is \code{..start}. + +\xsection{rdffmt}{\index{RDOFF}\codeindex{rdf}: \textindexlc{Relocatable Dynamic +Object File Format}} + +The \code{rdf} output format produces \code{RDOFF} object files. +\code{RDOFF} (Relocatable Dynamic Object File Format) is a home-grown +object-file format, designed alongside NASM itself and reflecting in +its file format the internal structure of the assembler. + +\code{RDOFF} is not used by any well-known operating systems. Those +writing their own systems, however, may well wish to use \code{RDOFF} +as their object format, on the grounds that it is designed primarily +for simplicity and contains very little file-header bureaucracy. + +The Unix NASM archive, and the DOS archive which includes sources, +both contain an \index{rdoff subdirectory}\code{rdoff} subdirectory +holding a set of RDOFF utilities: an RDF linker, an \code{RDF} +static-library manager, an RDF file dump utility, and a program +which will load and execute an RDF executable under Linux. + +\code{rdf} supports only the \index{standard section names} +\codeindex{.text}, \codeindex{.data} and \codeindex{.bss}. + +\xsubsection{rdflib}{Requiring a Library: The \codeindex{LIBRARY} Directive} + +\code{RDOFF} contains a mechanism for an object file to demand a given +library to be linked to the module, either at load time or run time. +This is done by the \code{LIBRARY} directive, which takes one argument +which is the name of the module: + +\begin{lstlisting} +library mylib.rdl +\end{lstlisting} + +\xsubsection{rdfmod}{Specifying a Module Name: The \codeindex{MODULE} Directive} + +Special \code{RDOFF} header record is used to store the name of the module. +It can be used, for example, by run-time loader to perform dynamic +linking. \code{MODULE} directive takes one argument which is the name +of current module: + +\begin{lstlisting} +module mymodname +\end{lstlisting} + +Note that when you statically link modules and tell linker to strip +the symbols from output file, all module names will be stripped too. +To avoid it, you should start module names with \index{\$!prefix}\code{\$}, +like: + +\begin{lstlisting} +module $kernel.core +\end{lstlisting} + +\xsubsection{rdfglob}{\code{rdf} Extensions to the \code{GLOBAL} Directive} +\index{GLOBAL!rdf extensions to} + +\code{RDOFF} global symbols can contain additional information needed by +the static linker. You can mark a global symbol as exported, thus +telling the linker do not strip it from target executable or library +file. Like in \code{ELF}, you can also specify whether an exported symbol +is a procedure (function) or data object. + +Suffixing the name with a colon and the word \codeindex{export} you make the +symbol exported: + +\begin{lstlisting} +global sys_open:export +\end{lstlisting} + +To specify that exported symbol is a procedure (function), you add the +word \codeindex{proc} or \codeindex{function} after declaration: + +\begin{lstlisting} +global sys_open:export proc +\end{lstlisting} + +Similarly, to specify exported data object, add the word \codeindex{data} +or \codeindex{object} to the directive: + +\begin{lstlisting} +global kernel_ticks:export data +\end{lstlisting} + +\xsubsection{rdfimpt}{\code{rdf} Extensions to the \code{EXTERN} Directive} +\index{EXTERN!rdf extensions to} + +By default the \code{EXTERN} directive in \code{RDOFF} declares a "pure external" +symbol (i.e. the static linker will complain if such a symbol is not resolved). +To declare an "imported" symbol, which must be resolved later during a dynamic +linking phase, \code{RDOFF} offers an additional \code{import} modifier. As in +\code{GLOBAL}, you can also specify whether an imported symbol is a procedure +(function) or data object. For example: + +\begin{lstlisting} +library $libc +extern _open:import +extern _printf:import proc +extern _errno:import data +\end{lstlisting} + +Here the directive \code{LIBRARY} is also included, which gives the dynamic linker +a hint as to where to find requested symbols. + +\xsection{dbgfmt}{\codeindex{dbg}: Debugging Format} + +The \code{dbg} format does not output an object file as such; instead, +it outputs a text file which contains a complete list of all the +transactions between the main body of NASM and the output-format +back end module. It is primarily intended to aid people who want to +write their own output drivers, so that they can get a clearer idea +of the various requests the main program makes of the output driver, +and in what order they happen. + +For simple files, one can easily use the \code{dbg} format like this: + +\begin{lstlisting} +nasm -f dbg filename.asm +\end{lstlisting} + +which will generate a diagnostic file called \code{filename.dbg}. +However, this will not work well on files which were designed for a +different object format, because each object format defines its own +macros (usually user-level forms of directives), and those macros +will not be defined in the \code{dbg} format. Therefore it can be +useful to run NASM twice, in order to do the preprocessing with the +native object format selected: + +\begin{lstlisting} +nasm -e -f rdf -o rdfprog.i rdfprog.asm +nasm -a -f dbg rdfprog.i +\end{lstlisting} + +This preprocesses \code{rdfprog.asm} into \code{rdfprog.i}, keeping the +\code{rdf} object format selected in order to make sure RDF special +directives are converted into primitive form correctly. Then the +preprocessed source is fed through the \code{dbg} format to generate +the final diagnostic output. + +This workaround will still typically not work for programs intended +for \code{obj} format, because the \code{obj}- \code{SEGMENT} and \code{GROUP} +directives have side effects of defining the segment and group names +as symbols; \code{dbg} will not do this, so the program will not +assemble. You will have to work around that by defining the symbols +yourself (using \code{EXTERN}, for example) if you really need to get a +\code{dbg} trace of an \code{obj}-specific source file. + +\code{dbg} accepts any section name and any directives at all, and logs +them all to its output file. + +\code{dbg} accepts and logs any \code{\%pragma}, but the specific \code{\%pragma}: + +\begin{lstlisting} +%pragma dbg maxdump <size> +\end{lstlisting} + +where \code{<size>} is either a number or \code{unlimited}, can be +used to control the maximum size for dumping the full contents of a +\code{rawdata} output object. diff --git a/doc/latex/src/preproc.tex b/doc/latex/src/preproc.tex new file mode 100644 index 00000000..17468602 --- /dev/null +++ b/doc/latex/src/preproc.tex @@ -0,0 +1,2400 @@ +% +% vim: ts=4 sw=4 et +% +\xchapter{preproc}{The NASM \textindexlc{Preprocessor}} + +NASM contains a powerful \textindex{macro processor}, which supports +conditional assembly, multi-level file inclusion, two forms of macro +(single-line and multi-line), and a ``context stack'' mechanism for +extra macro power. Preprocessor directives all begin with a \code{\%} +sign. + +The preprocessor collapses all lines which end with a backslash +\code{\textbackslash} character into a single line. +Thus: + +\begin{lstlisting} +%define THIS_VERY_LONG_MACRO_NAME_IS_DEFINED_TO \ + THIS_VALUE +\end{lstlisting} + +will work like a single-line macro without the backslash-newline +sequence. + +\xsection{slmacro}{\textindexlc{Single-Line Macros}} + +\xsubsection{define}{The Normal Way: \indexcode{\%idefine}\codeindex{\%define}} + +Single-line macros are defined using the \code{\%define} preprocessor +directive. The definitions work in a similar way to C; so you can do +things like + +\begin{lstlisting} +%define ctrl 0x1F & +%define param(a,b) ((a)+(a)*(b)) + + mov byte [param(2,ebx)], ctrl 'D' +\end{lstlisting} + +which will expand to + +\begin{lstlisting} + mov byte [(2)+(2)*(ebx)], 0x1F & 'D' +\end{lstlisting} + +When the expansion of a single-line macro contains tokens which +invoke another macro, the expansion is performed at invocation time, +not at definition time. Thus the code + +\begin{lstlisting} +%define a(x) 1+b(x) +%define b(x) 2*x + + mov ax,a(8) +\end{lstlisting} + +will evaluate in the expected way to \code{mov ax,1+2*8}, even though +the macro \code{b} wasn't defined at the time of definition of \code{a}. + +Macros defined with \code{\%define} are \textindex{case sensitive}: after +\code{\%define foo bar}, only \code{foo} will expand to \code{bar}: +\code{Foo} or \code{FOO} will not. By using \code{\%idefine} instead of +\code{\%define} (the ``i'' stands for ``insensitive'') you can define +all the case variants of a macro at once, so that \code{\%idefine foo bar} +would cause \code{foo}, \code{Foo}, \code{FOO}, \code{fOO} and so on +all to expand to \code{bar}. + +There is a mechanism which detects when a macro call has occurred as +a result of a previous expansion of the same macro, to guard against +\textindex{circular references} and infinite loops. If this happens, +the preprocessor will only expand the first occurrence of the macro. +Hence, if you code + +\begin{lstlisting} +%define a(x) 1+a(x) + + mov ax,a(3) +\end{lstlisting} + +the macro \code{a(3)} will expand once, becoming \code{1+a(3)}, and will +then expand no further. This behaviour can be useful: see \nref{32c} +for an example of its use. + +You can \index{overloading!single-line macros}overload single-line +macros: if you write + +\begin{lstlisting} +%define foo(x) 1+x +%define foo(x,y) 1+x*y +\end{lstlisting} + +the preprocessor will be able to handle both types of macro call, +by counting the parameters you pass; so \code{foo(3)} will become +\code{1+3} whereas \code{foo(ebx,2)} will become \code{1+ebx*2}. +However, if you define + +\begin{lstlisting} +%define foo bar +\end{lstlisting} + +then no other definition of \code{foo} will be accepted: a macro with +no parameters prohibits the definition of the same name as a macro +\emph{with} parameters, and vice versa. + +This doesn't prevent single-line macros being \emph{redefined}: +you can perfectly well define a macro with + +\begin{lstlisting} +%define foo bar +\end{lstlisting} + +and then re-define it later in the same source file with + +\begin{lstlisting} +%define foo baz +\end{lstlisting} + +Then everywhere the macro \code{foo} is invoked, it will be expanded +according to the most recent definition. This is particularly useful +when defining single-line macros with \code{\%assign} +(see \nref{assign}). + +You can \textindex{pre-define} single-line macros using the \code{-d} +option on the NASM command line: see \nref{opt-d}. + +\xsubsection{xdefine}{Resolving \code{\%define}: \indexcode{\%ixdefine}\codeindex{\%xdefine}} + +To have a reference to an embedded single-line macro resolved at the +time that the embedding macro is \emph{defined}, as opposed to when the +embedding macro is \emph{expanded}, you need a different mechanism to the +one offered by \code{\%define}. The solution is to use \code{\%xdefine}, or +it's \index{case sensitive}case-insensitive counterpart \code{\%ixdefine}. + +Suppose you have the following code: + +\begin{lstlisting} +%define isTrue 1 +%define isFalse isTrue +%define isTrue 0 + +val1: db isFalse + +%define isTrue 1 + +val2: db isFalse +\end{lstlisting} + +In this case, \code{val1} is equal to 0, and \code{val2} is equal to 1. +This is because, when a single-line macro is defined using \code{\%define}, +it is expanded only when it is called. As \code{isFalse} expands to \code{isTrue}, +the expansion will be the current value of \code{isTrue}. The first time it is called +that is 0, and the second time it is 1. + +If you wanted \code{isFalse} to expand to the value assigned to the +embedded macro \code{isTrue} at the time that \code{isFalse} was defined, +you need to change the above code to use \code{\%xdefine}. + +\begin{lstlisting} +%xdefine isTrue 1 +%xdefine isFalse isTrue +%xdefine isTrue 0 + +val1: db isFalse + +%xdefine isTrue 1 + +val2: db isFalse +\end{lstlisting} + +Now, each time that \code{isFalse} is called, it expands to 1, +as that is what the embedded macro \code{isTrue} expanded to at +the time that \code{isFalse} was defined. + +% FIXME the keys +\xsubsection{indmacro}{\textindexlc{Macro Indirection}: \indexcode{\%[}\code{\%[...]}} + +The \code{\%[...]} construct can be used to expand macros in contexts +where macro expansion would otherwise not occur, including in the +names other macros. For example, if you have a set of macros named +\code{Foo16}, \code{Foo32} and \code{Foo64}, you could write: + +\begin{lstlisting} +mov ax,Foo%[__BITS__] ; The Foo value +\end{lstlisting} + +to use the builtin macro \code{\_\_BITS\_\_} (see \nref{bitsm}) +to automatically select between them. Similarly, the two statements: + +\begin{lstlisting} +%xdefine Bar Quux ; Expands due to %xdefine +%define Bar %[Quux] ; Expands due to %[...] +\end{lstlisting} + +have, in fact, exactly the same effect. + +\code{\%[...]} concatenates to adjacent tokens in the same way that +multi-line macro parameters do, see \nref{concat} for details. + +% FIXME concatmacro key +\xsubsection{concatmacro}{Concatenating Single Line Macro Tokens: \codeindex{\%+}} + +Individual tokens in single line macros can be concatenated, to produce +longer tokens for later processing. This can be useful if there are +several similar macros that perform similar functions. + +Please note that a space is required after \code{\%+}, in order to +disambiguate it from the syntax \code{\%+1} used in multiline macros. + +As an example, consider the following: + +\begin{lstlisting} +%define BDASTART 400h ; Start of BIOS data area + +struc tBIOSDA ; its structure + .COM1addr RESW 1 + .COM2addr RESW 1 + ; ..and so on +endstruc +\end{lstlisting} + +Now, if we need to access the elements of tBIOSDA in different places, +we can end up with: + +\begin{lstlisting} +mov ax,BDASTART + tBIOSDA.COM1addr +mov bx,BDASTART + tBIOSDA.COM2addr +\end{lstlisting} + +This will become pretty ugly (and tedious) if used in many places, and +can be reduced in size significantly by using the following macro: + +\begin{lstlisting} +; Macro to access BIOS variables by their names (from tBDA): + +%define BDA(x) BDASTART + tBIOSDA. %+ x +\end{lstlisting} + +Now the above code can be written as: + +\begin{lstlisting} +mov ax,BDA(COM1addr) +mov bx,BDA(COM2addr) +\end{lstlisting} + +Using this feature, we can simplify references to a lot of macros +(and, in turn, reduce typing errors). + +% FIXME they key +\xsubsection{selfref}{The Macro Name Itself: \codeindex{\%?} and \codeindex{\%??}} + +The special symbols \code{\%?} and \code{\%??} can be used to +reference the macro name itself inside a macro expansion, +this is supported for both single-and multi-line macros. +\code{\%?} refers to the macro name as \emph{invoked}, whereas +\code{\%??} refers to the macro name as \emph{declared}. +The two are always the same for case-sensitive macros, but +for case-insensitive macros, they can differ. + +For example: + +\begin{lstlisting} +%idefine Foo mov %?,%?? + + foo + FOO +\end{lstlisting} + +will expand to: + +\begin{lstlisting} + mov foo,Foo + mov FOO,Foo +\end{lstlisting} + +The sequence: + +\begin{lstlisting} +%idefine keyword $%? +\end{lstlisting} + +can be used to make a keyword ``disappear'', for example in case a new +instruction has been used as a label in older code. For example: + +\begin{lstlisting} +%idefine pause $%? ; Hide the PAUSE instruction +\end{lstlisting} + +\xsubsection{undef}{Undefining Single-Line Macros: \codeindex{\%undef}} + +Single-line macros can be removed with the \code{\%undef} directive. +For example, the following sequence: + +\begin{lstlisting} +%define foo bar +%undef foo + + mov eax, foo +\end{lstlisting} + +will expand to the instruction \code{mov eax, foo}, since after +\code{\%undef} the macro \code{foo} is no longer defined. + +Macros that would otherwise be pre-defined can be undefined on the +command-line using the \code{-u} option on the NASM command line: +see \nref{opt-u}. + +\xsubsection{assign}{\textindex{Preprocessor Variables}: \codeindex{\%assign}} + +An alternative way to define single-line macros is by means of the +\code{\%assign} command (and its \index{case sensitive}case-insensitive +counterpart \codeindex{\%iassign}, which differs from \code{\%assign} in +exactly the same way that \code{\%idefine} differs from \code{\%define}). + +\code{\%assign} is used to define single-line macros which take no +parameters and have a numeric value. This value can be specified in +the form of an expression, and it will be evaluated once, when the +\code{\%assign} directive is processed. + +Like \code{\%define}, macros defined using \code{\%assign} can be +re-defined later, so you can do things like + +\begin{lstlisting} +%assign i i+1 +\end{lstlisting} + +to increment the numeric value of a macro. + +\code{\%assign} is useful for controlling the termination of \code{\%rep} +preprocessor loops: see \nref{rep} for an example of this. Another +use for \code{\%assign} is given in \nref{16c} and \nref{32c}. + +The expression passed to \code{\%assign} is a \textindex{critical expression} +(see \nref{crit}), and must also evaluate to a pure number +(rather than a relocatable reference such as a code or data address, +or anything involving a register). + +\xsubsection{defstr}{Defining Strings: \indexcode{\%idefstr}\codeindex{\%defstr}} + +\code{\%defstr}, and its case-insensitive counterpart \code{\%idefstr}, +define or redefine a single-line macro without parameters but converts +the entire right-hand side, after macro expansion, to a quoted string +before definition. + +For example: + +\begin{lstlisting} +%defstr test TEST +\end{lstlisting} + +is equivalent to + +\begin{lstlisting} +%define test 'TEST' +\end{lstlisting} + +This can be used, for example, with the \code{\%!} construct +(see \nref{getenv}): + +\begin{lstlisting} +%defstr PATH %!PATH ; The operating system PATH variable +\end{lstlisting} + +\xsubsection{deftok}{Defining Tokens: \indexcode{\%ideftok}\codeindex{\%deftok}} + +\code{\%deftok}, and its case-insensitive counterpart \code{\%ideftok}, +define or redefine a single-line macro without parameters but converts +the second parameter, after string conversion, to a sequence of tokens. + +For example: + +\begin{lstlisting} +%deftok test 'TEST' +\end{lstlisting} + +is equivalent to + +\begin{lstlisting} +%define test TEST +\end{lstlisting} + +\xsection{strmanip}{\textindexlc{String Manipulation in Macros}} + +It's often useful to be able to handle strings in macros. NASM +supports a few simple string handling macro operators from which +more complex operations can be constructed. + +All the string operators define or redefine a value (either a string +or a numeric value) to a single-line macro. When producing a string +value, it may change the style of quoting of the input string or +strings, and possibly use \code{\textbackslash}-escapes inside +\code{`}-quoted strings. + +\xsubsection{strcat}{\textindexlc{Concatenating Strings}: \codeindex{\%strcat}} + +The \code{\%strcat} operator concatenates quoted strings and assign +them to a single-line macro. + +For example: + +\begin{lstlisting} +%strcat alpha "Alpha: ", '12" screen' +\end{lstlisting} + +would assign the value \code{'Alpha: 12" screen'} to \code{alpha}. +Similarly: + +\begin{lstlisting} +%strcat beta '"foo"\', "'bar'" +\end{lstlisting} + +would assign the value \code{`"foo" \textbackslash \textbackslash 'bar'`} +to \code{beta}. + +The use of commas to separate strings is permitted but optional. + +\xsubsection{strlen}{\textindexlc{String Length}: \codeindex{\%strlen}} + +The \code{\%strlen} operator assigns the length of a string to a macro. +For example: + +\begin{lstlisting} +%strlen charcnt 'my string' +\end{lstlisting} + +In this example, \code{charcnt} would receive the value 9, just as +if an \code{\%assign} had been used. In this example, \code{'my string'} +was a literal string but it could also have been a single-line +macro that expands to a string, as in the following example: + +\begin{lstlisting} +%define sometext 'my string' +%strlen charcnt sometext +\end{lstlisting} + +As in the first case, this would result in \code{charcnt} being +assigned the value of 9. + +\xsubsection{substr}{\textindexlc{Extracting Substrings}: \codeindex{\%substr}} + +Individual letters or substrings in strings can be extracted using the +\code{\%substr} operator. An example of its use is probably more useful +than the description: + +\begin{lstlisting} +%substr mychar 'xyzw' 1 ; equivalent to %define mychar 'x' +%substr mychar 'xyzw' 2 ; equivalent to %define mychar 'y' +%substr mychar 'xyzw' 3 ; equivalent to %define mychar 'z' +%substr mychar 'xyzw' 2,2 ; equivalent to %define mychar 'yz' +%substr mychar 'xyzw' 2,-1 ; equivalent to %define mychar 'yzw' +%substr mychar 'xyzw' 2,-2 ; equivalent to %define mychar 'yz' +\end{lstlisting} + +As with \code{\%strlen} (see \nref{strlen}), the first +parameter is the single-line macro to be created and the second +is the string. The third parameter specifies the first character +to be selected, and the optional fourth parameter (preceeded by comma) +is the length. Note that the first index is 1, not 0 and the last +index is equal to the value that \code{\%strlen} would assign given +the same string. Index values out of range result in an empty string. +A negative length means ``until N-1 characters before the end of string'', +i.e. \code{-1} means until end of string, \code{-2} until one character +before, etc. + +\xsection{mlmacro}{\textindexlc{Multi-Line Macros}: \indexcode{\%imacro}\codeindex{\%macro}} + +Multi-line macros are much more like the type of macro seen in MASM +and TASM: a multi-line macro definition in NASM looks something like +this. + +\begin{lstlisting} +%macro prologue 1 + + push ebp + mov ebp,esp + sub esp,%1 + +%endmacro +\end{lstlisting} + +This defines a C-like function prologue as a macro: so you would +invoke the macro with a call such as + +\begin{minipage}{\linewidth} +\begin{lstlisting} +myfunc: prologue 12 +\end{lstlisting} +\end{minipage} + +which would expand to the three lines of code + +\begin{lstlisting} +myfunc: push ebp + mov ebp,esp + sub esp,12 +\end{lstlisting} + +The number \code{1} after the macro name in the \code{\%macro} line +defines the number of parameters the macro \code{prologue} expects +to receive. The use of \code{\%1} inside the macro definition refers +to the first parameter to the macro call. With a macro taking more +than one parameter, subsequent parameters would be referred to as +\code{\%2}, \code{\%3} and so on. + +Multi-line macros, like single-line macros, are \textindex{case-sensitive}, +unless you define them using the alternative directive \code{\%imacro}. + +If you need to pass a comma as \emph{part} of a parameter to a +multi-line macro, you can do that by enclosing the entire parameter +in \index{braces!around macro parameters}braces. So you could code +things like + +\begin{lstlisting} +%macro silly 2 + + %2: db %1 + +%endmacro + + silly 'a', letter_a ; letter_a: db 'a' + silly 'ab', string_ab ; string_ab: db 'ab' + silly {13,10}, crlf ; crlf: db 13,10 +\end{lstlisting} + +\xsubsection{mlmacover}{Overloading Multi-Line Macros} +\index{overloading!multi-line macros} + +As with single-line macros, multi-line macros can be overloaded by +defining the same macro name several times with different numbers of +parameters. This time, no exception is made for macros with no +parameters at all. So you could define + +\begin{lstlisting} +%macro prologue 0 + + push ebp + mov ebp,esp + +%endmacro +\end{lstlisting} + +to define an alternative form of the function prologue which +allocates no local stack space. + +Sometimes, however, you might want to ``overload'' a machine +instruction; for example, you might want to define + +\begin{lstlisting} +%macro push 2 + + push %1 + push %2 + +%endmacro +\end{lstlisting} + +so that you could code + +\begin{lstlisting} + push ebx ; this line is not a macro call + push eax,ecx ; but this one is +\end{lstlisting} + +Ordinarily, NASM will give a warning for the first of the above two +lines, since \code{push} is now defined to be a macro, and is being +invoked with a number of parameters for which no definition has been +given. The correct code will still be generated, but the assembler +will give a warning. This warning can be disabled by the use of the +\code{-w-macro-params} command-line option (see \nref{opt-w}). + +\xsubsection{maclocal}{\textindexlc{Macro-Local Labels}} + +NASM allows you to define labels within a multi-line macro definition +in such a way as to make them local to the macro call: so calling +the same macro multiple times will use a different label each time. +You do this by prefixing \codeindex{\%\%} to the label name. +So you can invent an instruction which executes a \code{RET} if the +\code{Z} flag is set by doing this: + +\begin{lstlisting} +%macro retz 0 + + jnz %%skip + ret + %%skip: + +%endmacro +\end{lstlisting} + +You can call this macro as many times as you want, and every time +you call it NASM will make up a different ``real'' name to substitute +for the label \code{\%\%skip}. The names NASM invents are of the form +\code{..@2345.skip}, where the number 2345 changes with every macro +call. The \codeindex{..@} prefix prevents macro-local labels from +interfering with the local label mechanism, as described in +\nref{locallab}. You should avoid defining your own labels +in this form (the \code{..@} prefix, then a number, then another period) +in case they interfere with macro-local labels. + +\xsubsection{mlmacgre}{\textindexlc{Greedy Macro Parameters}} + +Occasionally it is useful to define a macro which lumps its entire +command line into one parameter definition, possibly after +extracting one or two smaller parameters from the front. An example +might be a macro to write a text string to a file in MS-DOS, where +you might want to be able to write + +\begin{lstlisting} +writefile [filehandle],"hello, world",13,10 +\end{lstlisting} + +NASM allows you to define the last parameter of a macro to be +\emph{greedy}, meaning that if you invoke the macro with more +parameters than it expects, all the spare parameters get lumped into +the last defined one along with the separating commas. So if you +code: + +\begin{lstlisting} +%macro writefile 2+ + + jmp %%endstr + %%str: db %2 + %%endstr: + mov dx,%%str + mov cx,%%endstr-%%str + mov bx,%1 + mov ah,0x40 + int 0x21 + +%endmacro +\end{lstlisting} + +then the example call to \code{writefile} above will work as expected: +the text before the first comma, \code{[filehandle]}, is used as the +first macro parameter and expanded when \code{\%1} is referred to, and +all the subsequent text is lumped into \code{\%2} and placed after the +\code{db}. + +The greedy nature of the macro is indicated to NASM by the use of +the \index{modifier!+}\code{+} sign after the parameter count on the +\code{\%macro} line. + +If you define a greedy macro, you are effectively telling NASM how +it should expand the macro given \emph{any} number of parameters from +the actual number specified up to infinity; in this case, for +example, NASM now knows what to do when it sees a call to +\code{writefile} with 2, 3, 4 or more parameters. NASM will take this +into account when overloading macros, and will not allow you to +define another form of \code{writefile} taking 4 parameters (for +example). + +Of course, the above macro could have been implemented as a +non-greedy macro, in which case the call to it would have had to +look like + +\begin{lstlisting} +writefile [filehandle], {"hello, world",13,10} +\end{lstlisting} + +NASM provides both mechanisms for putting \textindex{commas in macro +parameters}, and you choose which one you prefer for each macro +definition. + +See \nref{sectmac} for a better way to write the above macro. + +\xsubsection{mlmacrange}{\textindexlc{Macro Parameters Range}} + +NASM allows you to expand parameters via special construction \code{\%\{x:y\}} +where \code{x} is the first parameter index and \code{y} is the last. +Any index can be either negative or positive but must never be zero. + +For example + +\begin{lstlisting} +%macro mpar 1-* + db %{3:5} +%endmacro + +mpar 1,2,3,4,5,6 +\end{lstlisting} + +expands to \code{3,4,5} range. + +Even more, the parameters can be reversed so that + +\begin{lstlisting} +%macro mpar 1-* + db %{5:3} +%endmacro + +mpar 1,2,3,4,5,6 +\end{lstlisting} + +expands to \code{5,4,3} range. + +But even this is not the last. The parameters can be addressed via negative +indices so NASM will count them reversed. The ones who know Python may see +the analogue here. + +\begin{lstlisting} +%macro mpar 1-* + db %{-1:-3} +%endmacro + +mpar 1,2,3,4,5,6 +\end{lstlisting} + +expands to \code{6,5,4} range. + +Note that NASM uses \textindex{comma} to separate parameters being expanded. + +By the way, here is a trick - you might use the index \code{\%{-1:-1}} +which gives you the \textindex{last} argument passed to a macro. + +\xsubsection{mlmacdef}{\textindexlc{Default Macro Parameters}} + +NASM also allows you to define a multi-line macro with a \emph{range} +of allowable parameter counts. If you do this, you can specify +defaults for \textindex{omitted parameters}. So, for example: + +\begin{lstlisting} +%macro die 0-1 "Painful program death has occurred." + + writefile 2,%1 + mov ax,0x4c01 + int 0x21 + +%endmacro +\end{lstlisting} + +This macro (which makes use of the \code{writefile} macro defined in +\nref{mlmacgre}) can be called with an explicit error message, +which it will display on the error output stream before exiting, or it can be +called with no parameters, in which case it will use the default +error message supplied in the macro definition. + +In general, you supply a minimum and maximum number of parameters +for a macro of this type; the minimum number of parameters are then +required in the macro call, and then you provide defaults for the +optional ones. So if a macro definition began with the line + +\begin{lstlisting} +%macro foobar 1-3 eax,[ebx+2] +\end{lstlisting} + +then it could be called with between one and three parameters, and +\code{\%1} would always be taken from the macro call. \code{\%2}, if not +specified by the macro call, would default to \code{eax}, and \code{\%3} +if not specified would default to \code{[ebx+2]}. + +You can provide extra information to a macro by providing +too many default parameters: + +\begin{lstlisting} +%macro quux 1 something +\end{lstlisting} + +This will trigger a warning by default; see \nref{opt-w} for +more information. +When \code{quux} is invoked, it receives not one but two parameters. +\code{something} can be referred to as \code{\%2}. The difference +between passing \code{something} this way and writing \code{something} +in the macro body is that with this way \code{something} is evaluated +when the macro is defined, not when it is expanded. + +You may omit parameter defaults from the macro definition, in which +case the parameter default is taken to be blank. This can be useful +for macros which can take a variable number of parameters, since the +\codeindex{\%0} token (see \nref{percent0}) allows you to +determine how many parameters were really passed to the macro call. + +This defaulting mechanism can be combined with the greedy-parameter +mechanism; so the \code{die} macro above could be made more powerful, +and more useful, by changing the first line of the definition to + +\begin{lstlisting} +%macro die 0-1+ "Painful program death has occurred.",13,10 +\end{lstlisting} + +The maximum parameter count can be infinite, denoted by \code{*}. In +this case, of course, it is impossible to provide a \emph{full} set of +default parameters. Examples of this usage are shown in +\nref{rotate}. + +\xsubsection{percent0}{\codeindex{\%0}: \index{counting macro parameters}Macro Parameter Counter} + +The parameter reference \code{\%0} will return a numeric constant giving the +number of parameters received, that is, if \code{\%0} is n then \code{\%}n +is the last parameter. \code{\%0} is mostly useful for macros that can take a variable +number of parameters. It can be used as an argument to \code{\%rep} +(see \nref{rep}) in order to iterate through all the parameters +of a macro. Examples are given in \nref{rotate}. + +\xsubsection{percent00}{\codeindex{\%00}: \index{label preceeding macro}Label Preceeding Macro} + +\code{\%00} will return the label preceeding the macro invocation, if any. The +label must be on the same line as the macro invocation, may be a local label +(see \nref{locallab}), and need not end in a colon. + +\xsubsection{rotate}{\codeindex{\%rotate}: \textindexlc{Rotating Macro Parameters}} + +Unix shell programmers will be familiar with the \index{shift +command}\code{shift} shell command, which allows the arguments passed +to a shell script (referenced as \code{\$1}, \code{\$2} and so on) to be +moved left by one place, so that the argument previously referenced +as \code{\$2} becomes available as \code{\$1}, and the argument previously +referenced as \code{\$1} is no longer available at all. + +NASM provides a similar mechanism, in the form of \code{\%rotate}. As +its name suggests, it differs from the Unix \code{shift} in that no +parameters are lost: parameters rotated off the left end of the +argument list reappear on the right, and vice versa. + +\code{\%rotate} is invoked with a single numeric argument (which may be +an expression). The macro parameters are rotated to the left by that +many places. If the argument to \code{\%rotate} is negative, the macro +parameters are rotated to the right. + +\index{iterating over macro parameters}So a pair of macros to save and +restore a set of registers might work as follows: + +\begin{lstlisting} +%macro multipush 1-* + + %rep %0 + push %1 + %rotate 1 + %endrep + +%endmacro +\end{lstlisting} + +This macro invokes the \code{PUSH} instruction on each of its arguments +in turn, from left to right. It begins by pushing its first +argument, \code{\%1}, then invokes \code{\%rotate} to move all the arguments +one place to the left, so that the original second argument is now +available as \code{\%1}. Repeating this procedure as many times as there +were arguments (achieved by supplying \code{\%0} as the argument to +\code{\%rep}) causes each argument in turn to be pushed. + +Note also the use of \code{*} as the maximum parameter count, +indicating that there is no upper limit on the number of parameters +you may supply to the \codeindex{multipush} macro. + +It would be convenient, when using this macro, to have a \code{POP} +equivalent, which \emph{didn't} require the arguments to be given in +reverse order. Ideally, you would write the \code{multipush} macro +call, then cut-and-paste the line to where the pop needed to be +done, and change the name of the called macro to \code{multipop}, and +the macro would take care of popping the registers in the opposite +order from the one in which they were pushed. + +This can be done by the following definition: + +\begin{lstlisting} +%macro multipop 1-* + + %rep %0 + %rotate -1 + pop %1 + %endrep + +%endmacro +\end{lstlisting} + +This macro begins by rotating its arguments one place to the +\emph{right}, so that the original \emph{last} argument appears +as \code{\%1}. This is then popped, and the arguments are rotated +right again, socthe second-to-last argument becomes \code{\%1}. +Thus the arguments are iterated through in reverse order. + +\xsubsection{concat}{\textindexlc{Concatenating Macro Parameters}} + +NASM can concatenate macro parameters and macro indirection constructs +on to other text surrounding them. This allows you to declare a family +of symbols, for example, in a macro definition. If, for example, you +wanted to generate a table of key codes along with offsets into the +table, you could code something like + +\begin{lstlisting} +%macro keytab_entry 2 + + keypos%1 equ $-keytab + db %2 + +%endmacro + +keytab: + keytab_entry F1,128+1 + keytab_entry F2,128+2 + keytab_entry Return,13 +\end{lstlisting} + +which would expand to + +\begin{lstlisting} +keytab: +keyposF1 equ $-keytab + db 128+1 +keyposF2 equ $-keytab + db 128+2 +keyposReturn equ $-keytab + db 13 +\end{lstlisting} + +You can just as easily concatenate text on to the other end of a +macro parameter, by writing \code{\%1foo}. + +If you need to append a \emph{digit} to a macro parameter, for example +defining labels \code{foo1} and \code{foo2} when passed the parameter +\code{foo}, you can't code \code{\%11} because that would be taken as the +eleventh macro parameter. Instead, you must code +\index{braces!after \% sign}\code{\%\{1\}1}, which will separate the first +\code{1} (giving the number of the macro parameter) from the second +(literal text to be concatenated to the parameter). + +This concatenation can also be applied to other preprocessor in-line +objects, such as macro-local labels (\nref{maclocal}) +and context-local labels (\nref{ctxlocal}). +In all cases, ambiguities in syntax can be resolved by enclosing +everything after the \code{\%} sign and before the literal text +in braces: so \code{\%\{\%foo\}bar} concatenates the text \code{bar} +to the end of the real name of the macro-local label \code{\%\%foo}. +(This is unnecessary, since the form NASM uses for the real names of +macro-local labels means that the two usages \code{\%\{\%foo\}bar} +and \code{\%\%foobar} would both expand to the same +thing anyway; nevertheless, the capability is there.) + +The single-line macro indirection construct, \code{\%[...]} +(\nref{indmacro}), behaves the same way as macro +parameters for the purpose of concatenation. + +See also the \code{\%+} operator, \nref{concatmacro}. + +\xsubsection{mlmaccc}{\textindexlc{Condition Codes as Macro Parameters}} + +NASM can give special treatment to a macro parameter which contains +a condition code. For a start, you can refer to the macro parameter +\code{\%1} by means of the alternative syntax \codeindex{\%+1}, +which informs NASM that this macro parameter is supposed to contain +a condition code, and will cause the preprocessor to report an +error message if the macro is called with a parameter which is +\emph{not} a valid condition code. + +Far more usefully, though, you can refer to the macro parameter by +means of \codeindex{\%-1}, which NASM will expand as the \emph{inverse} +condition code. So the \code{retz} macro defined in \nref{maclocal} +can be replaced by a general \textindexlc{conditional-return macro} like this: + +\begin{lstlisting} +%macro retc 1 + + j%-1 %%skip + ret + %%skip: + +%endmacro +\end{lstlisting} + +This macro can now be invoked using calls like \code{retc ne}, which +will cause the conditional-jump instruction in the macro expansion +to come out as \code{JE}, or \code{retc po} which will make the jump a +\code{JPE}. + +The \code{\%+1} macro-parameter reference is quite happy to interpret +the arguments \code{CXZ} and \code{ECXZ} as valid condition codes; +however, \code{\%-1} will report an error if passed either of these, +because no inverse condition code exists. + +\xsubsection{nolist}{\textindexlc{Disabling Listing Expansion}\indexcode{.nolist}} + +When NASM is generating a listing file from your program, it will +generally expand multi-line macros by means of writing the macro +call and then listing each line of the expansion. This allows you to +see which instructions in the macro expansion are generating what +code; however, for some macros this clutters the listing up +unnecessarily. + +NASM therefore provides the \code{.nolist} qualifier, which you can +include in a macro definition to inhibit the expansion of the macro +in the listing file. The \code{.nolist} qualifier comes directly after +the number of parameters, like this: + +\begin{lstlisting} +%macro foo 1.nolist +\end{lstlisting} + +Or like this: + +\begin{lstlisting} +%macro bar 1-5+.nolist a,b,c,d,e,f,g,h +\end{lstlisting} + +\xsubsection{unmacro}{Undefining Multi-Line Macros: \codeindex{\%unmacro}} + +Multi-line macros can be removed with the \code{\%unmacro} directive. +Unlike the \code{\%undef} directive, however, \code{\%unmacro} takes an +argument specification, and will only remove \textindex{exact matches} with +that argument specification. + +For example: + +\begin{lstlisting} +%macro foo 1-3 + ; Do something +%endmacro +%unmacro foo 1-3 +\end{lstlisting} + +removes the previously defined macro \code{foo}, but + +\begin{lstlisting} +%macro bar 1-3 + ; Do something +%endmacro +%unmacro bar 1 +\end{lstlisting} + +does \emph{not} remove the macro \code{bar}, since the argument +specification does not match exactly. + +\xsection{condasm}{\textindexlc{Conditional Assembly}\indexcode{\%if}} + +Similarly to the C preprocessor, NASM allows sections of a source +file to be assembled only if certain conditions are met. The general +syntax of this feature looks like this: + +\begin{lstlisting} +%if<condition> + ; some code which only appears if <condition> is met +%elif<condition2> + ; only appears if <condition> is not met but <condition2> is +%else + ; this appears if neither <condition> nor <condition2> was met +%endif +\end{lstlisting} + +The inverse forms \codeindex{\%ifn} and \codeindex{\%elifn} are also supported. + +The \codeindex{\%else} clause is optional, as is the \codeindex{\%elif} clause. +You can have more than one \code{\%elif} clause as well. + +There are a number of variants of the \code{\%if} directive. Each has its +corresponding \code{\%elif}, \code{\%ifn}, and \code{\%elifn} directives; for +example, the equivalents to the \code{\%ifdef} directive are \code{\%elifdef}, +\code{\%ifndef}, and \code{\%elifndef}. + +\xsubsection{ifdef}{\codeindex{\%ifdef}: Testing Single-Line Macro Existence +\index{testing, single-line macro existence}} + +Beginning a conditional-assembly block with the line \code{\%ifdef MACRO} +will assemble the subsequent code if, and only if, a single-line macro called +\code{MACRO} is defined. If not, then the \code{\%elif} and \code{\%else} +blocks (if any) will be processed instead. + +For example, when debugging a program, you might want to write code +such as + +\begin{lstlisting} + ; perform some function +%ifdef DEBUG + writefile 2,"Function performed successfully",13,10 +%endif + ; go and do something else +\end{lstlisting} + +Then you could use the command-line option \code{-dDEBUG} to create a +version of the program which produced debugging messages, and remove +the option to generate the final release version of the program. + +You can test for a macro \emph{not} being defined by using +\codeindex{\%ifndef} instead of \code{\%ifdef}. You can also test +for macro definitions in \code{\%elif} blocks by using +\codeindex{\%elifdef} and \codeindex{\%elifndef}. + +\xsubsection{ifmacro}{\codeindex{\%ifmacro}: Testing Multi-Line Macro Existence +\index{testing!multi-line macro existence}} + +The \code{\%ifmacro} directive operates in the same way as the \code{\%ifdef} +directive, except that it checks for the existence of a multi-line macro. + +For example, you may be working with a large project and not have control +over the macros in a library. You may want to create a macro with one +name if it doesn't already exist, and another name if one with that name +does exist. + +The \code{\%ifmacro} is considered true if defining a macro with the given name +and number of arguments would cause a definitions conflict. For example: + +\begin{lstlisting} +%ifmacro MyMacro 1-3 + + %error "MyMacro 1-3" causes a conflict with an existing macro. + +%else + + %macro MyMacro 1-3 + + ; insert code to define the macro + + %endmacro + +%endif +\end{lstlisting} + +This will create the macro ``\code{MyMacro 1-3}'' if no macro already exists which +would conflict with it, and emits a warning if there would be a definition +conflict. + +You can test for the macro not existing by using the \codeindex{\%ifnmacro} +instead of \code{\%ifmacro}. Additional tests can be performed in +\code{\%elif} blocks by using \codeindex{\%elifmacro} and +\codeindex{\%elifnmacro}. + +\xsubsection{ifctx}{\codeindex{\%ifctx}: Testing the Context Stack +\index{testing!context stack}} + +The conditional-assembly construct \code{\%ifctx} will cause the +subsequent code to be assembled if and only if the top context on +the preprocessor's context stack has the same name as one of the arguments. +As with \code{\%ifdef}, the inverse and \code{\%elif} forms \codeindex{\%ifnctx}, +\codeindex{\%elifctx} and \codeindex{\%elifnctx} are also supported. + +For more details of the context stack, see \nref{ctxstack}. +For a sample use of \code{\%ifctx}, see \nref{blockif}. + +\xsubsection{if}{\codeindex{\%if}: Testing Arbitrary Numeric Expressions} +\index{testing!arbitrary numeric expressions} + +The conditional-assembly construct \code{\%if expr} will cause the +subsequent code to be assembled if and only if the value of the +numeric expression \code{expr} is non-zero. An example of the use of +this feature is in deciding when to break out of a \code{\%rep} +preprocessor loop: see \nref{rep} for a detailed example. + +The expression given to \code{\%if}, and its counterpart +\codeindex{\%elif}, is a critical expression (see \nref{crit}). + +\code{\%if} extends the normal NASM expression syntax, by providing a +set of \textindexlc{relational operators} which are not normally available in +expressions. The operators \codeindex{=}, \codeindex{\textless}, +\codeindex{\textgreater}, \codeindex{\textless=}, \codeindex{\textgreater=} +and \codeindex{\textless\textgreater} test equality, +less-than, greater-than, less-or-equal, greater-or-equal and not-equal +respectively. The C-like forms \codeindex{==} and \codeindex{!=} are +supported as alternative forms of \code{=} and \code{\textless\textgreater}. +In addition, low-priority logical operators \codeindex{\&\&}, +\codeindex{\^{}\^{}} and \codeindex{||} are provided, supplying +\textindex{logical!ND}, \textindex{logical!XOR} and \textindex{logical!OR}. +These work like the C logical operators (although C has no logical XOR), +in that they always return either 0 or 1, and treat any non-zero input as 1 +(so that \code{\^{}\^{}}, for example, returns 1 if exactly one of its inputs +is zero, and 0 otherwise). The relational operators also return 1 +for true and 0 for false. + +Like other \code{\%if} constructs, \code{\%if} has a counterpart +\codeindex{\%elif}, and negative forms \codeindex{\%ifn} and \codeindex{\%elifn}. + +\xsubsection{ifidn}{\codeindex{\%ifidn} and \codeindex{\%ifidni}: Testing Exact Text Identity} +\index{testing!exact text identity} + +The construct \code{\%ifidn text1,text2} will cause the subsequent code +to be assembled if and only if \code{text1} and \code{text2}, after +expanding single-line macros, are identical pieces of text. +Differences in white space are not counted. + +\code{\%ifidni} is similar to \code{\%ifidn}, but is \textindex{case-insensitive}. + +For example, the following macro pushes a register or number on the +stack, and allows you to treat \code{IP} as a real register: + +\begin{lstlisting} +%macro pushparam 1 + + %ifidni %1,ip + call %%label + %%label: + %else + push %1 + %endif + +%endmacro +\end{lstlisting} + +Like other \code{\%if} constructs, \code{\%ifidn} has a counterpart +\codeindex{\%elifidn}, and negative forms \codeindex{\%ifnidn} and +\codeindex{\%elifnidn}. Similarly, \code{\%ifidni} has counterparts +\codeindex{\%elifidni}, \codeindex{\%ifnidni} and \codeindex{\%elifnidni}. + +\xsubsection{iftyp}{\codeindex{\%ifid}, \codeindex{\%ifnum}, \codeindex{\%ifstr}: Testing Token Types} +\index{testing!token types} + +Some macros will want to perform different tasks depending on +whether they are passed a number, a string, or an identifier. For +example, a string output macro might want to be able to cope with +being passed either a string constant or a pointer to an existing +string. + +The conditional assembly construct \code{\%ifid}, taking one parameter +(which may be blank), assembles the subsequent code if and only if +the first token in the parameter exists and is an identifier. +\code{\%ifnum} works similarly, but tests for the token being a numeric +constant; \code{\%ifstr} tests for it being a string. + +For example, the \code{writefile} macro defined in \nref{mlmacgre} +can be extended to take advantage of \code{\%ifstr} in the following fashion: + +\begin{lstlisting} +%macro writefile 2-3+ + + %ifstr %2 + jmp %%endstr + %if %0 = 3 + %%str: db %2,%3 + %else + %%str: db %2 + %endif + %%endstr: mov dx,%%str + mov cx,%%endstr-%%str + %else + mov dx,%2 + mov cx,%3 + %endif + mov bx,%1 + mov ah,0x40 + int 0x21 + +%endmacro +\end{lstlisting} + +Then the \code{writefile} macro can cope with being called in either of +the following two ways: + +\begin{lstlisting} +writefile [file], strpointer, length +writefile [file], "hello", 13, 10 +\end{lstlisting} + +In the first, \code{strpointer} is used as the address of an +already-declared string, and \code{length} is used as its length; in +the second, a string is given to the macro, which therefore declares +it itself and works out the address and length for itself. + +Note the use of \code{\%if} inside the \code{\%ifstr}: this is to detect +whether the macro was passed two arguments (so the string would be a +single string constant, and \code{db \%2} would be adequate) or more (in +which case, all but the first two would be lumped together into +\code{\%3}, and \code{db \%2,\%3} would be required). + +The usual \indexcode{\%elifid}\indexcode{\%elifnum}\indexcode{\%elifstr}\code{\%elif}..., +\indexcode{\%ifnid}\indexcode{\%ifnnum}\indexcode{\%ifnstr}\code{\%ifn}..., and +\indexcode{\%elifnid}\indexcode{\%elifnnum}\indexcode{\%elifnstr}\code{\%elifn}... +versions exist for each of \code{\%ifid}, \code{\%ifnum} and \code{\%ifstr}. + +\xsubsection{iftoken}{\codeindex{\%iftoken}: Test for a Single Token} + +Some macros will want to do different things depending on if it is +passed a single token (e.g. paste it to something else using \code{\%+}) +versus a multi-token sequence. + +The conditional assembly construct \code{\%iftoken} assembles the +subsequent code if and only if the expanded parameters consist of +exactly one token, possibly surrounded by whitespace. + +For example: + +\begin{lstlisting} +%iftoken 1 +\end{lstlisting} + +will assemble the subsequent code, but + +\begin{lstlisting} +%iftoken -1 +\end{lstlisting} + +will not, since \code{-1} contains two tokens: the unary minus operator +\code{-}, and the number \code{1}. + +The usual \codeindex{\%eliftoken}, \codeindex{\%ifntoken}, and +\codeindex{\%elifntoken} variants are also provided. + +\xsubsection{ifempty}{\codeindex{\%ifempty}: Test for Empty Expansion} + +The conditional assembly construct \code{\%ifempty} assembles the +subsequent code if and only if the expanded parameters do not contain +any tokens at all, whitespace excepted. + +The usual \codeindex{\%elifempty}, \codeindex{\%ifnempty}, and +\codeindex{\%elifnempty} variants are also provided. + +\xsubsection{ifenv}{\codeindex{\%ifenv}: Test If Environment Variable Exists} + +The conditional assembly construct \code{\%ifenv} assembles the +subsequent code if and only if the environment variable referenced by +the \code{\%^^21}\emph{variable} directive exists. + +The usual \codeindex{\%elifenv}, \codeindex{\%ifnenv}, and \codeindex{\%elifnenv} +variants are also provided. + +Just as for \code{\%^^21}\emph{variable} the argument should be written as a +string if it contains characters that would not be legal in an +identifier. See \nref{getenv}. + +\xsection{rep}{\textindexlc{Preprocessor Loops}\index{repeating code}: \codeindex{\%rep}} + +NASM's \code{TIMES} prefix, though useful, cannot be used to invoke a +multi-line macro multiple times, because it is processed by NASM +after macros have already been expanded. Therefore NASM provides +another form of loop, this time at the preprocessor level: \code{\%rep}. + +The directives \code{\%rep} and \codeindex{\%endrep} (\code{\%rep} +takes a numeric argument, which can be an expression; \code{\%endrep} +takes no arguments) can be used to enclose a chunk of code, which is then +replicated as many times as specified by the preprocessor: + +\begin{lstlisting} +%assign i 0 +%rep 64 + inc word [table+2*i] +%assign i i+1 +%endrep +\end{lstlisting} + +This will generate a sequence of 64 \code{INC} instructions, +incrementing every word of memory from \code{[table]} to +\code{[table+126]}. + +For more complex termination conditions, or to break out of a repeat +loop part way along, you can use the \codeindex{\%exitrep} directive to +terminate the loop, like this: + +\begin{lstlisting} +fibonacci: +%assign i 0 +%assign j 1 +%rep 100 +%if j > 65535 + %exitrep +%endif + dw j +%assign k j+i +%assign i j +%assign j k +%endrep + +fib_number equ ($-fibonacci)/2 +\end{lstlisting} + +This produces a list of all the Fibonacci numbers that will fit in +16 bits. Note that a maximum repeat count must still be given to +\code{\%rep}. This is to prevent the possibility of NASM getting into an +infinite loop in the preprocessor, which (on multitasking or +multi-user systems) would typically cause all the system memory to +be gradually used up and other applications to start crashing. + +Note a maximum repeat count is limited by 62 bit number, though it +is hardly possible that you ever need anything bigger. + +\xsection{files}{Source Files and Dependencies} + +These commands allow you to split your sources into multiple files. + +\xsubsection{include}{\codeindex{\%include}: \textindexlc{Including Other Files}} + +Using, once again, a very similar syntax to the C preprocessor, +NASM's preprocessor lets you include other source files into your +code. This is done by the use of the \codeindex{\%include} directive: + +\begin{lstlisting} +%include "macros.mac" +\end{lstlisting} + +will include the contents of the file \code{macros.mac} into the source +file containing the \code{\%include} directive. + +Include files are \index{searching for include files}searched for in the +current directory (the directory you're in when you run NASM, as +opposed to the location of the NASM executable or the location of +the source file), plus any directories specified on the NASM command +line using the \code{-i} option. + +The standard C idiom for preventing a file being included more than +once is just as applicable in NASM: if the file \code{macros.mac} has +the form + +\begin{lstlisting} +%ifndef MACROS_MAC + %define MACROS_MAC + ; now define some macros +%endif +\end{lstlisting} + +then including the file more than once will not cause errors, +because the second time the file is included nothing will happen +because the macro \code{MACROS\_MAC} will already be defined. + +You can force a file to be included even if there is no \code{\%include} +directive that explicitly includes it, by using the \codeindex{-p} option +on the NASM command line (see \nref{opt-p}). + +\xsubsection{pathsearch}{\codeindex{\%pathsearch}: Search the Include Path} + +The \code{\%pathsearch} directive takes a single-line macro name and a +filename, and declare or redefines the specified single-line macro to +be the \emph{include-path-resolved} version of the filename, if the file +exists (otherwise, it is passed unchanged). + +For example, + +\begin{lstlisting} +%pathsearch MyFoo "foo.bin" +\end{lstlisting} + +... with \code{-Ibins/} in the include path may end up defining the macro +\code{MyFoo} to be \code{"bins/foo.bin"}. + +\xsubsection{depend}{\codeindex{\%depend}: Add Dependent Files} + +The \code{\%depend} directive takes a filename and adds it to the list of +files to be emitted as dependency generation when the \code{-M} options +and its relatives (see \nref{opt-M}) are used. It produces +no output. + +This is generally used in conjunction with \code{\%pathsearch}. For +example, a simplified version of the standard macro wrapper for the +\code{INCBIN} directive looks like: + +\begin{lstlisting} +%imacro incbin 1-2+ 0 +%pathsearch dep %1 +%depend dep + incbin dep,%2 +%endmacro +\end{lstlisting} + +This first resolves the location of the file into the macro \code{dep}, +then adds it to the dependency lists, and finally issues the +assembler-level \code{INCBIN} directive. + +\xsubsection{use}{\codeindex{\%use}: Include Standard Macro Package} + +The \code{\%use} directive is similar to \code{\%include}, but rather than +including the contents of a file, it includes a named standard macro +package. The standard macro packages are part of NASM, and are +described in \nref{macropkg}. + +Unlike the \code{\%include} directive, package names for the \code{\%use} +directive do not require quotes, but quotes are permitted. In NASM +2.04 and 2.05 the unquoted form would be macro-expanded; this is no +longer true. Thus, the following lines are equivalent: + +\begin{lstlisting} +%use altreg +%use 'altreg' +\end{lstlisting} + +Standard macro packages are protected from multiple inclusion. When a +standard macro package is used, a testable single-line macro of the +form \code{\_\_USE\_\emph{package}\_\_} is also defined, +see \nref{usedef}. + +\xsection{ctxstack}{The \textindexlc{Context Stack}} + +Having labels that are local to a macro definition is sometimes not +quite powerful enough: sometimes you want to be able to share labels +between several macro calls. An example might be a \code{REPEAT} ... +\code{UNTIL} loop, in which the expansion of the \code{REPEAT} macro +would need to be able to refer to a label which the \code{UNTIL} macro +had defined. However, for such a macro you would also want to be +able to nest these loops. + +NASM provides this level of power by means of a \emph{context stack}. +The preprocessor maintains a stack of \emph{contexts}, each of which is +characterized by a name. You add a new context to the stack using +the \codeindex{\%push} directive, and remove one using \codeindex{\%pop}. +You can define labels that are local to a particular context on the stack. + +\xsubsection{pushpop}{\codeindex{\%push} and \codeindex{\%pop}: Creating and Removing Contexts} +\index{context!create} +\index{context!remove } + +The \code{\%push} directive is used to create a new context and place it +on the top of the context stack. \code{\%push} takes an optional argument, +which is the name of the context. For example: + +\begin{lstlisting} +%push foobar +\end{lstlisting} + +This pushes a new context called \code{foobar} on the stack. You can have +several contexts on the stack with the same name: they can still be +distinguished. If no name is given, the context is unnamed (this is +normally used when both the \code{\%push} and the \code{\%pop} are inside a +single macro definition.) + +The directive \code{\%pop}, taking one optional argument, removes the top +context from the context stack and destroys it, along with any +labels associated with it. If an argument is given, it must match the +name of the current context, otherwise it will issue an error. + +\xsubsection{ctxlocal}{\textindexlc{Context-Local Labels}} + +Just as the usage \code{\%\%foo} defines a label which is local to the +particular macro call in which it is used, the usage \indexcode{\%\$}\code{\%\$foo} +is used to define a label which is local to the context on the top +of the context stack. So the \code{REPEAT} and \code{UNTIL} example given +above could be implemented by means of: + +\begin{lstlisting} +%macro repeat 0 + + %push repeat + %$begin: + +%endmacro + +%macro until 1 + + j%-1 %$begin + %pop + +%endmacro +\end{lstlisting} + +and invoked by means of, for example, + +\begin{lstlisting} +mov cx,string +repeat +add cx,3 +scasb +until e +\end{lstlisting} + +which would scan every fourth byte of a string in search of the byte +in \code{AL}. + +If you need to define, or access, labels local to the context +\emph{below} the top one on the stack, you can use +\indexcode{\%\$\$}\code{\%\$\$foo}, or \code{\%\$\$\$foo} for +the context below that, and so on. + +\xsubsection{ctxdefine}{\textindexlc{Context-Local Single-Line Macros}} + +NASM also allows you to define single-line macros which are local to +a particular context, in just the same way: + +\begin{lstlisting} +%define %$localmac 3 +\end{lstlisting} + +will define the single-line macro \code{\%\$localmac} to be local to the +top context on the stack. Of course, after a subsequent \code{\%push}, +it can then still be accessed by the name \code{\%\$\$localmac}. + +\xsubsection{ctxfallthrough}{\textindexlc{Context Fall-Through Lookup} \emph{(deprecated)}} + +Context fall-through lookup (automatic searching of outer contexts) +is a feature that was added in NASM version 0.98.03. Unfortunately, +this feature is unintuitive and can result in buggy code that would +have otherwise been prevented by NASM's error reporting. As a result, +this feature has been \emph{deprecated}. NASM version 2.09 will issue a +warning when usage of this \emph{deprecated} feature is detected. Starting +with NASM version 2.10, usage of this \emph{deprecated} feature will simply +result in an \emph{expression syntax error}. + +An example usage of this \emph{deprecated} feature follows: + +\begin{lstlisting} +%macro ctxthru 0 +%push ctx1 + %assign %$external 1 + %push ctx2 + %assign %$internal 1 + mov eax, %$external + mov eax, %$internal + %pop +%pop +%endmacro +\end{lstlisting} + +As demonstrated, \code{\%\$external} is being defined in the \code{ctx1} +context and referenced within the \code{ctx2} context. With context +fall-through lookup, referencing an undefined context-local macro +like this implicitly searches through all outer contexts until a match +is made or isn't found in any context. As a result, \code{\%\$external} +referenced within the \code{ctx2} context would implicitly use \code{\%\$external} +as defined in \code{ctx1}. Most people would expect NASM to issue an error in +this situation because \code{\%\$external} was never defined within \code{ctx2} +and also isn't qualified with the proper context depth, \code{\%\$\$external}. + +Here is a revision of the above example with proper context depth: + +\begin{lstlisting} +%macro ctxthru 0 +%push ctx1 + %assign %$external 1 + %push ctx2 + %assign %$internal 1 + mov eax, %$$external + mov eax, %$internal + %pop +%pop +%endmacro +\end{lstlisting} + +As demonstrated, \code{\%\$external} is still being defined in the \code{ctx1} +context and referenced within the \code{ctx2} context. However, the +reference to \code{\%\$external} within \code{ctx2} has been fully qualified with +the proper context depth, \code{\%\$\$external}, and thus is no longer ambiguous, +unintuitive or erroneous. + +\xsubsection{ctxrepl}{\codeindex{\%repl}: Renaming a Context} +\index{context!rename} + +If you need to change the name of the top context on the stack (in +order, for example, to have it respond differently to \code{\%ifctx}), +you can execute a \code{\%pop} followed by a \code{\%push}; but this will +have the side effect of destroying all context-local labels and +macros associated with the context that was just popped. + +NASM provides the directive \code{\%repl}, which \emph{replaces} a context +with a different name, without touching the associated macros and +labels. So you could replace the destructive code + +\begin{lstlisting} +%pop +%push newname +\end{lstlisting} + +with the non-destructive version \code{\%repl newname}. + +\xsubsection{blockif}{Example Use of the \textindexlc{Context Stack}: +\textindexlc{Block IFs}} + +This example makes use of almost all the context-stack features, +including the conditional-assembly construct \codeindex{\%ifctx}, to +implement a block IF statement as a set of macros. + +\begin{lstlisting} +%macro if 1 + + %push if + j%-1 %$ifnot + +%endmacro + +%macro else 0 + + %ifctx if + %repl else + jmp %$ifend + %$ifnot: + %else + %error "expected `if' before `else'" + %endif + +%endmacro + +%macro endif 0 + + %ifctx if + %$ifnot: + %pop + %elifctx else + %$ifend: + %pop + %else + %error "expected `if' or `else' before `endif'" + %endif + +%endmacro +\end{lstlisting} + +This code is more robust than the \code{REPEAT} and \code{UNTIL} macros +given in \nref{ctxlocal}, because it uses conditional assembly to check +that the macros are issued in the right order (for example, not calling \code{endif} +before \code{if}) and issues a \code{\%error} if they're not. + +In addition, the \code{endif} macro has to be able to cope with the two +distinct cases of either directly following an \code{if}, or following +an \code{else}. It achieves this, again, by using conditional assembly +to do different things depending on whether the context on top of +the stack is \code{if} or \code{else}. + +The \code{else} macro has to preserve the context on the stack, in +order to have the \code{\%\$ifnot} referred to by the \code{if} macro be the +same as the one defined by the \code{endif} macro, but has to change +the context's name so that \code{endif} will know there was an +intervening \code{else}. It does this by the use of \code{\%repl}. + +A sample usage of these macros might look like: + +\begin{lstlisting} +cmp ax,bx + +if ae + cmp bx,cx + + if ae + mov ax,cx + else + mov ax,bx + endif + +else + cmp ax,cx + + if ae + mov ax,cx + endif + +endif +\end{lstlisting} + +The block-\code{IF} macros handle nesting quite happily, by means of +pushing another context, describing the inner \code{if}, on top of the +one describing the outer \code{if}; thus \code{else} and \code{endif} +always refer to the last unmatched \code{if} or \code{else}. + +\xsection{stackrel}{\textindexlc{Stack Relative Preprocessor Directives}} + +The following preprocessor directives provide a way to use +labels to refer to local variables allocated on the stack: + +\begin{itemize} + \item{\code{\%arg} (see \nref{arg});} + \item{\code{\%stacksize} (see \nref{stacksize});} + \item{\code{\%local} (see \nref{local}).} +\end{itemize} + +\xsubsection{arg}{\codeindex{\%arg} Directive} + +The \code{\%arg} directive is used to simplify the handling of +parameters passed on the stack. Stack based parameter passing +is used by many high level languages, including C, C++ and Pascal. + +While NASM has macros which attempt to duplicate this functionality +(see \nref{16cmacro}), the syntax is not particularly convenient +to use and is not TASM compatible. Here is an example which shows the use +of \code{\%arg} without any external macros: + +\begin{lstlisting} +some_function: + + %push mycontext ; save the current context + %stacksize large ; tell NASM to use bp + %arg i:word, j_ptr:word + + mov ax,[i] + mov bx,[j_ptr] + add ax,[bx] + ret + + %pop ; restore original context +\end{lstlisting} + +This is similar to the procedure defined in \nref{16cmacro} +and adds the value in i to the value pointed to by j\_ptr and returns +the sum in the ax register. See \nref{pushpop} for an +explanation of \code{push} and \code{pop} and the use of context stacks. + +\xsubsection{stacksize}{\codeindex{\%stacksize} Directive} + +The \code{\%stacksize} directive is used in conjunction with the +\code{\%arg} (see \nref{arg}) and the \code{\%local} +(see \nref{local}) directives. It tells NASM the default +size to use for subsequent \code{\%arg} and \code{\%local} directives. +The \code{\%stacksize} directive takes one required argument +which is one of \code{flat}, \code{flat64}, \code{large} or \code{small}. + +\begin{lstlisting} +%stacksize flat +\end{lstlisting} + +This form causes NASM to use stack-based parameter addressing +relative to \code{ebp} and it assumes that a near form of call +was used to get to this label (i.e. that \code{eip} is on the stack). + +\begin{lstlisting} +%stacksize flat64 +\end{lstlisting} + +This form causes NASM to use stack-based parameter addressing +relative to \code{rbp} and it assumes that a near form of call was used +to get to this label (i.e. that \code{rip} is on the stack). + +\begin{lstlisting} +%stacksize large +\end{lstlisting} + +This form uses \code{bp} to do stack-based parameter addressing and +assumes that a far form of call was used to get to this address +(i.e. that \code{ip} and \code{cs} are on the stack). + +\begin{lstlisting} +%stacksize small +\end{lstlisting} + +This form also uses \code{bp} to address stack parameters, but it is +different from \code{large} because it also assumes that the old value +of bp is pushed onto the stack (i.e. it expects an \code{ENTER} +instruction). In other words, it expects that \code{bp}, \code{ip} and +\code{cs} are on the top of the stack, underneath any local space which +may have been allocated by \code{ENTER}. This form is probably most +useful when used in combination with the \code{\%local} directive +(see \nref{local}). + +\xsubsection{local}{\codeindex{\%local} Directive} + +The \code{\%local} directive is used to simplify the use of local +temporary stack variables allocated in a stack frame. Automatic +local variables in C are an example of this kind of variable. The +\code{\%local} directive is most useful when used with the \code{\%stacksize} +(see \nref{stacksize} and is also compatible with the \code{\%arg} directive +(see \nref{arg}). It allows simplified reference to variables on the +stack which have been allocated typically by using the \code{ENTER} +instruction. +% (see \nref{insENTER} for a description of that instruction). +An example of its use is the following: + +\begin{lstlisting} +silly_swap: + + %push mycontext ; save the current context + %stacksize small ; tell NASM to use bp + %assign %$localsize 0 ; see text for explanation + %local old_ax:word, old_dx:word + + enter %$localsize,0 ; see text for explanation + mov [old_ax],ax ; swap ax & bx + mov [old_dx],dx ; and swap dx & cx + mov ax,bx + mov dx,cx + mov bx,[old_ax] + mov cx,[old_dx] + leave ; restore old bp + ret ; + + %pop ; restore original context +\end{lstlisting} + +The \code{\%\$localsize} variable is used internally by the +\code{\%local} directive and \emph{must} be defined within the +current context before the \code{\%local} directive may be used. +Failure to do so will result in one expression syntax error for +each \code{\%local} variable declared. It then may be used in +the construction of an appropriately sized ENTER instruction +as shown in the example. + +\xsection{pperror}{Reporting \textindexlc{User-Defined Errors}: +\codeindex{\%error}, \codeindex{\%warning}, \codeindex{\%fatal}} + +The preprocessor directive \code{\%error} will cause NASM to report an +error if it occurs in assembled code. So if other users are going to +try to assemble your source files, you can ensure that they define the +right macros by means of code like this: + +\begin{lstlisting} +%ifdef F1 + ; do some setup +%elifdef F2 + ; do some different setup +%else + %error "Neither F1 nor F2 was defined." +%endif +\end{lstlisting} + +Then any user who fails to understand the way your code is supposed +to be assembled will be quickly warned of their mistake, rather than +having to wait until the program crashes on being run and then not +knowing what went wrong. + +Similarly, \code{\%warning} issues a warning, but allows assembly to continue: + +\begin{lstlisting} +%ifdef F1 + ; do some setup +%elifdef F2 + ; do some different setup +%else + %warning "Neither F1 nor F2 was defined, assuming F1." + %define F1 +%endif +\end{lstlisting} + +\code{\%error} and \code{\%warning} are issued only on the final assembly +pass. This makes them safe to use in conjunction with tests that +depend on symbol values. + +\code{\%fatal} terminates assembly immediately, regardless of pass. This +is useful when there is no point in continuing the assembly further, +and doing so is likely just going to cause a spew of confusing error +messages. + +It is optional for the message string after \code{\%error}, \code{\%warning} +or \code{\%fatal} to be quoted. If it is \emph{not}, then single-line macros +are expanded in it, which can be used to display more information to +the user. For example: + +\begin{lstlisting} +%if foo > 64 + %assign foo_over foo-64 + %error foo is foo_over bytes too large +%endif +\end{lstlisting} + +\xsection{otherpreproc}{\textindexlc{Other Preprocessor Directives}} + +\xsubsection{line}{\codeindex{\%line} Directive} + +The \code{\%line} directive is used to notify NASM that the input line +corresponds to a specific line number in another file. Typically +this other file would be an original source file, with the current +NASM input being the output of a pre-processor. The \code{\%line} +directive allows NASM to output messages which indicate the line +number of the original source file, instead of the file that is being +read by NASM. + +This preprocessor directive is not generally used directly by +programmers, but may be of interest to preprocessor authors. The +usage of the \code{\%line} preprocessor directive is as follows: + +\begin{lstlisting} +%line nnn[+mmm] [filename] +\end{lstlisting} + +In this directive, \code{nnn} identifies the line of the original source +file which this line corresponds to. \code{mmm} is an optional parameter +which specifies a line increment value; each line of the input file +read in is considered to correspond to \code{mmm} lines of the original +source file. Finally, \code{filename} is an optional parameter which +specifies the file name of the original source file. + +After reading a \code{\%line} preprocessor directive, NASM will report +all file name and line numbers relative to the values specified +therein. + +If the command line option \codeindex{--no-line} is given, all \code{\%line} +directives are ignored. This may be useful for debugging preprocessed +code. See \nref{opt-no-line}. + +\xsubsection{getenv}{\codeindex{\%^^21\emph{variable}}: Read an Environment Variable} + +The \code{\%^^21\emph{variable}} directive makes it possible to read the +value of an environment variable at assembly time. This could, for example, +be used to store the contents of an environment variable into a string, which +could be used at some other point in your code. + +For example, suppose that you have an environment variable \code{FOO}, +and you want the contents of \code{FOO} to be embedded in your program as +a quoted string. You could do that as follows: + +\begin{lstlisting} +%defstr FOO %!FOO +\end{lstlisting} + +See \nref{defstr} for notes on the \code{\%defstr} directive. + +If the name of the environment variable contains non-identifier +characters, you can use string quotes to surround the name of the +variable, for example: + +\begin{lstlisting} +%defstr C_colon %!'C:' +\end{lstlisting} + +\xsection{stdmac}{\textindexlc{Standard Macros}} + +NASM defines a set of standard macros, which are already defined +when it starts to process any source file. If you really need a +program to be assembled with no pre-defined macros, you can use the +\codeindex{\%clear} directive to empty the preprocessor of everything +but context-local preprocessor variables and single-line macros. + +Most \textindex{user-level assembler directives} are implemented as macros +which invoke primitive directives; these are described in \nref{directive}. +The rest of the standard macro set is described here. + +\xsubsection{stdmacver}{\textindexlc{NASM Version} Macros} + +The single-line macros \codeindex{\_\_NASM\_MAJOR\_\_}, \codeindex{\_\_NASM\_MINOR\_\_}, +\codeindex{\_\_NASM\_SUBMINOR\_\_} and \codeindex{\_\_NASM\_PATCHLEVEL\_\_} expand to +the major, minor, subminor and patch level parts of the \textindexlc{version number of NASM} +being used. So, under NASM 0.98.32p1 for example, \code{\_\_NASM\_MAJOR\_\_} +would be defined to be 0, \code{\_\_NASM\_MINOR\_\_} would be defined as 98, +\code{\_\_NASM\_SUBMINOR\_\_} would be defined to 32, and \code{\_\_NASM\_PATCHLEVEL\_\_} +would be defined as 1. + +Additionally, the macro \codeindex{\_\_NASM\_SNAPSHOT\_\_} is defined for +automatically generated snapshot releases \emph{only}. + +\xsubsection{stdmacverid}{\codeindex{\_\_NASM\_VERSION\_ID\_\_}: +\textindexlc{NASM Version ID}} + +The single-line macro \code{\_\_NASM\_VERSION\_ID\_\_} expands to a dword integer +representing the full version number of the version of nasm being used. +The value is the equivalent to \code{\_\_NASM\_MAJOR\_\_}, \code{\_\_NASM\_MINOR\_\_}, +\code{\_\_NASM\_SUBMINOR\_\_} and \code{\_\_NASM\_PATCHLEVEL\_\_} concatenated to +produce a single doubleword. Hence, for 0.98.32p1, the returned number +would be equivalent to: + +\begin{lstlisting} +dd 0x00622001 +\end{lstlisting} + +or + +\begin{lstlisting} +db 1,32,98,0 +\end{lstlisting} + +Note that the above lines are generate exactly the same code, the second +line is used just to give an indication of the order that the separate +values will be present in memory. + + +\xsubsection{stdmacverstr}{\codeindex{\_\_NASM\_VER\_\_}: +\textindexlc{NASM Version string}} + +The single-line macro \code{\_\_NASM\_VER\_\_} expands to a string which defines +the version number of nasm being used. So, under NASM 0.98.32 for example, + +\begin{lstlisting} +db __NASM_VER__ +\end{lstlisting} + +would expand to + +\begin{lstlisting} +db "0.98.32" +\end{lstlisting} + +\xsubsection{fileline}{\codeindex{\_\_FILE\_\_} and \codeindex{\_\_LINE\_\_}: +File Name and Line Number} + +Like the C preprocessor, NASM allows the user to find out the file +name and line number containing the current instruction. The macro +\code{\_\_FILE\_\_} expands to a string constant giving the name of the +current input file (which may change through the course of assembly +if \code{\%include} directives are used), and \code{\_\_LINE\_\_} expands +to a numeric constant giving the current line number in the input file. + +These macros could be used, for example, to communicate debugging +information to a macro, since invoking \code{\_\_LINE\_\_} inside a macro +definition (either single-line or multi-line) will return the line +number of the macro \emph{call}, rather than \emph{definition}. So to +determine where in a piece of code a crash is occurring, for example, +one could write a routine \code{stillhere}, which is passed a line number +in \code{EAX} and outputs something like "line 155: still here". +You could then write a macro + +\begin{lstlisting} +%macro notdeadyet 0 + push eax + mov eax,__LINE__ + call stillhere + pop eax +%endmacro +\end{lstlisting} + +and then pepper your code with calls to \c{notdeadyet} until you +find the crash point. + +\xsubsection{bitsm}{\codeindex{\_\_BITS\_\_}: Current BITS Mode} + +The \code{\_\_BITS\_\_} standard macro is updated every time that the BITS +mode is set using the \code{BITS XX} or \code{[BITS XX]} directive, +where XX is a valid mode number of 16, 32 or 64. \code{\_\_BITS\_\_} receives +the specified mode number and makes it globally available. This can be very +useful for those who utilize mode-dependent macros. + +\xsubsection{ofmtm}{\codeindex{\_\_OUTPUT\_FORMAT\_\_}: Current Output Format} + +The \code{\_\_OUTPUT\_FORMAT\_\_} standard macro holds the current output +format name, as given by the \code{-f} option or NASM's default. Type +\code{nasm -hf} for a list. + +\begin{lstlisting} +%ifidn __OUTPUT_FORMAT__, win32 + %define NEWLINE 13, 10 +%elifidn __OUTPUT_FORMAT__, elf32 + %define NEWLINE 10 +%endif +\end{lstlisting} + +\xsubsection{dfmtm}{\codeindex{\_\_DEBUG\_FORMAT\_\_}: +Current Debug Format} + +If debugging information generation is enabled, The +\code{\_\_DEBUG\_FORMAT\_\_} standard macro holds the current +debug format name as specified by the \code{-F} or \code{-g} option +or the output format default. Type \code{nasm -f} \emph{output} +\code{y} for a list. + +\code{\_\_DEBUG\_FORMAT\_\_} is not defined if debugging is not +enabled, or if the debug format specified is \code{null}. + +\xsubsection{datetime}{Assembly Date and Time Macros} + +NASM provides a variety of macros that represent the timestamp of the +assembly session. + +\begin{itemize} + \item{The \codeindex{\_\_DATE\_\_} and \codeindex{\_\_TIME\_\_} + macros give the assembly date and time as strings, in ISO 8601 + format (\code{"YYYY-MM-DD"} and \code{"HH:MM:SS"}, respectively).} + + \item{The \codeindex{\_\_DATE\_NUM\_\_} and \codeindex{\_\_TIME\_NUM\_\_} + macros give the assembly date and time in numeric form; in the format + \code{YYYYMMDD} and \code{HHMMSS} respectively.} + + \item{The \codeindex{\_\_UTC\_DATE\_\_} and \codeindex{\_\_UTC\_TIME\_\_} + macros give the assembly date and time in universal time (UTC) as strings, + in ISO 8601 format (\code{"YYYY-MM-DD"} and \code{"HH:MM:SS"}, respectively). + If the host platform doesn't provide UTC time, these macros are undefined.} + + \item{The \codeindex{\_\_UTC\_DATE\_NUM\_\_} and \codeindex{\_\_UTC\_TIME\_NUM\_\_} + macros give the assembly date and time universal time (UTC) in numeric form; + in the format \code{YYYYMMDD} and \code{HHMMSS} respectively. If the + host platform doesn't provide UTC time, these macros are undefined.} + + \item{The \code{\_\_POSIX\_TIME\_\_} macro is defined as a number containing + the number of seconds since the POSIX epoch, 1 January 1970 00:00:00 UTC; + excluding any leap seconds. This is computed using UTC time if + available on the host platform, otherwise it is computed using the + local time as if it was UTC.} +\end{itemize} + +All instances of time and date macros in the same assembly session +produce consistent output. For example, in an assembly session +started at 42 seconds after midnight on January 1, 2010 in Moscow +(timezone UTC+3) these macros would have the following values, +assuming, of course, a properly configured environment with a correct +clock: + +\begin{lstlisting} +__DATE__ "2010-01-01" +__TIME__ "00:00:42" +__DATE_NUM__ 20100101 +__TIME_NUM__ 000042 +__UTC_DATE__ "2009-12-31" +__UTC_TIME__ "21:00:42" +__UTC_DATE_NUM__ 20091231 +__UTC_TIME_NUM__ 210042 +__POSIX_TIME__ 1262293242 +\end{lstlisting} + +\xsubsection{usedef}{\indexcode{\_\_USE\_*\_\_}\code{\_\_USE\_} +\emph{package}\code{\_\_}: Package Include Test} + +When a standard macro package (see \nref{macropkg}) is included with the +\code{\%use} directive (see \nref{use}), a single-line macro of +the form \code{\_\_USE\_}\emph{package}\code{\_\_} is automatically defined. +This allows testing if a particular package is invoked or not. + +For example, if the \code{altreg} package is included (see \nref{pkgaltreg}), +then the macro \code{\_\_USE\_ALTREG\_\_} is defined. + +\xsubsection{passdef}{\codeindex{\_\_PASS\_\_}: Assembly Pass} + +The macro \code{\_\_PASS\_\_} is defined to be \code{1} on preparatory passes, +and \code{2} on the final pass. In preprocess-only mode, it is set to +\code{3}, and when running only to generate dependencies (due to the +\code{-M} or \code{-MG} option, see \nref{opt-M}) it is set to \code{0}. + +\emph{Avoid using this macro if at all possible. It is tremendously easy +to generate very strange errors by misusing it, and the semantics may +change in future versions of NASM.} + +\xsubsection{struc}{\codeindex{STRUC} and \codeindex{ENDSTRUC}: +\textindexlc{Declaring Structure} Data Types} + +The core of NASM contains no intrinsic means of defining data +structures; instead, the preprocessor is sufficiently powerful that +data structures can be implemented as a set of macros. The macros +\code{STRUC} and \code{ENDSTRUC} are used to define a structure +data type. + +\code{STRUC} takes one or two parameters. The first parameter is the name +of the data type. The second, optional parameter is the base offset of +the structure. The name of the data type is defined as a symbol with +the value of the base offset, and the name of the data type with the +suffix \code{\_size} appended to it is defined as an \code{EQU} giving +the size of the structure. Once \code{STRUC} has been issued, you are +defining the structure, and should define fields using the \code{RESB} +family of pseudo-instructions, and then invoke \code{ENDSTRUC} to finish +the definition. + +For example, to define a structure called \code{mytype} containing a +longword, a word, a byte and a string of bytes, you might code + +\begin{lstlisting} +struc mytype + mt_long: resd 1 + mt_word: resw 1 + mt_byte: resb 1 + mt_str: resb 32 +endstruc +\end{lstlisting} + +The above code defines six symbols: \code{mt\_long} as 0 (the offset +from the beginning of a \code{mytype} structure to the longword field), +\code{mt\_word} as 4, \code{mt\_byte} as 6, \code{mt\_str} as 7, +\code{mytype\_size} as 39, and \code{mytype} itself as zero. + +The reason why the structure type name is defined at zero by default +is a side effect of allowing structures to work with the local label +mechanism: if your structure members tend to have the same names in +more than one structure, you can define the above structure like this: + +\begin{lstlisting} +struc mytype + .long: resd 1 + .word: resw 1 + .byte: resb 1 + .str: resb 32 +endstruc +\end{lstlisting} + +This defines the offsets to the structure fields as \code{mytype.long}, +\code{mytype.word}, \code{mytype.byte} and \code{mytype.str}. + +NASM, since it has no \emph{intrinsic} structure support, does not +support any form of period notation to refer to the elements of a +structure once you have one (except the above local-label notation), +so code such as \code{mov ax,[mystruc.mt\_word]} is not valid. +\code{mt\_word} is a constant just like any other constant, so the +correct syntax is \code{mov ax,[mystruc+mt\_word]} or +\code{mov ax,[mystruc+mytype.word]}. + +Sometimes you only have the address of the structure displaced by an +offset. For example, consider this standard stack frame setup: + +\begin{lstlisting} +push ebp +mov ebp, esp +sub esp, 40 +\end{lstlisting} + +In this case, you could access an element by subtracting the offset: + +\begin{lstlisting} +mov [ebp - 40 + mytype.word], ax +\end{lstlisting} + +However, if you do not want to repeat this offset, you can use -40 as +a base offset: + +\begin{lstlisting} +struc mytype, -40 +\end{lstlisting} + +And access an element this way: + +\begin{lstlisting} +mov [ebp + mytype.word], ax +\end{lstlisting} + +\xsubsection{istruc}{\codeindex{ISTRUC}, \codeindex{AT} and +\codeindex{IEND}: Declaring} +\textindexlc{Instances of Structures} + +Having defined a structure type, the next thing you typically want +to do is to declare instances of that structure in your data +segment. NASM provides an easy way to do this in the \code{ISTRUC} +mechanism. To declare a structure of type \code{mytype} in a program, +you code something like this: + +\begin{lstlisting} +mystruc: + istruc mytype + at mt_long, dd 123456 + at mt_word, dw 1024 + at mt_byte, db 'x' + at mt_str, db 'hello, world', 13, 10, 0 + iend +\end{lstlisting} + +The function of the \code{AT} macro is to make use of the \code{TIMES} +prefix to advance the assembly position to the correct point for the +specified structure field, and then to declare the specified data. +Therefore the structure fields must be declared in the same order as +they were specified in the structure definition. + +If the data to go in a structure field requires more than one source +line to specify, the remaining source lines can easily come after +the \code{AT} line. For example: + +\begin{lstlisting} +at mt_str, db 123,134,145,156,167,178,189 + db 190,100,0 +\end{lstlisting} + +Depending on personal taste, you can also omit the code part of the +\code{AT} line completely, and start the structure field on the next +line: + +\begin{lstlisting} +at mt_str + db 'hello, world' + db 13,10,0 +\end{lstlisting} + +\xsubsection{align}{\codeindex{ALIGN} and \codeindex{ALIGNB}: Data Alignment} + +The \code{ALIGN} and \code{ALIGNB} macros provides a convenient way to +align code or data on a word, longword, paragraph or other boundary. +Some assemblers call this directive \codeindex{EVEN}. The syntax of the +\code{ALIGN} and \code{ALIGNB} macros is + +\begin{lstlisting} +align 4 ; align on 4-byte boundary +align 16 ; align on 16-byte boundary +align 8,db 0 ; pad with 0s rather than NOPs +align 4,resb 1 ; align to 4 in the BSS +alignb 4 ; equivalent to previous line +\end{lstlisting} + +Both macros require their first argument to be a power of two; they +both compute the number of additional bytes required to bring the +length of the current section up to a multiple of that power of two, +and then apply the \code{TIMES} prefix to their second argument to +perform the alignment. + +If the second argument is not specified, the default for \code{ALIGN} +is \code{NOP}, and the default for \code{ALIGNB} is \code{RESB 1}. +So if the second argument is specified, the two macros are equivalent. +Normally, you can just use \code{ALIGN} in code and data sections and +\code{ALIGNB} in BSS sections, and never need the second argument +except for special purposes. + +\code{ALIGN} and \code{ALIGNB}, being simple macros, perform no error +checking: they cannot warn you if their first argument fails to be a +power of two, or if their second argument generates more than one +byte of code. In each of these cases they will silently do the wrong +thing. + +\code{ALIGNB} (or \code{ALIGN} with a second argument of \code{RESB 1}) +can be used within structure definitions: + +\begin{lstlisting} +struc mytype2 + mt_byte: + resb 1 + alignb 2 + mt_word: + resw 1 + alignb 4 + mt_long: + resd 1 + mt_str: + resb 32 +endstruc +\end{lstlisting} + +This will ensure that the structure members are sensibly aligned +relative to the base of the structure. + +A final caveat: \code{ALIGN} and \code{ALIGNB} work relative to the +beginning of the \emph{section}, not the beginning of the address space +in the final executable. Aligning to a 16-byte boundary when the +section you're in is only guaranteed to be aligned to a 4-byte +boundary, for example, is a waste of effort. Again, NASM does not +check that the section's alignment characteristics are sensible for +the use of \code{ALIGN} or \code{ALIGNB}. + +Both \code{ALIGN} and \code{ALIGNB} do call \code{SECTALIGN} macro implicitly. +See \nref{sectalign} for details. + +See also the \code{smartalign} standard macro package, \nref{pkgsmartalign}. + +\xsubsection{sectalign}{\codeindex{SECTALIGN}: Section Alignment} + +The \code{SECTALIGN} macros provides a way to modify alignment attribute +of output file section. Unlike the \code{align=} attribute (which is allowed +at section definition only) the \code{SECTALIGN} macro may be used at any time. + +For example the directive + +\begin{lstlisting} +SECTALIGN 16 +\end{lstlisting} + +sets the section alignment requirements to 16 bytes. Once increased it can +not be decreased, the magnitude may grow only. + +Note that \code{ALIGN} (see \nref{align}) calls the \code{SECTALIGN} +macro implicitly so the active section alignment requirements may be updated. +This is by default behaviour, if for some reason you want the \code{ALIGN} +do not call \code{SECTALIGN} at all use the directive + +\begin{lstlisting} +SECTALIGN OFF +\end{lstlisting} + +It is still possible to turn in on again by + +\begin{lstlisting} +SECTALIGN ON +\end{lstlisting} diff --git a/doc/latex/src/running.tex b/doc/latex/src/running.tex new file mode 100644 index 00000000..9cd0d363 --- /dev/null +++ b/doc/latex/src/running.tex @@ -0,0 +1,902 @@ +% +% vim: ts=4 sw=4 et +% +\xchapter{run}{Running NASM} + +\xsection{cmdline}{NASM \textindexlc{Command-Line} Syntax} + +To assemble a file, you issue a command of the form + +\begin{lstlisting} +nasm -f <format> <filename> [-o <output>] +\end{lstlisting} + +For example, + +\begin{lstlisting} +nasm -f elf myfile.asm +\end{lstlisting} + +will assemble \code{myfile.asm} into an ``ELF'' object +file \code{myfile.o}. And + +\begin{lstlisting} +nasm -f bin myfile.asm -o myfile.com +\end{lstlisting} + +will assemble ``myfile.asm'' into a raw binary file ``myfile.com''. + +To produce a listing file, with the hex codes output from NASM +displayed on the left of the original sources, use the \code{-l} +option to give a listing file name, for example: + +\begin{lstlisting} +nasm -f coff myfile.asm -l myfile.lst +\end{lstlisting} + +To get further usage instructions from NASM, try typing + +\begin{lstlisting} +nasm -h +\end{lstlisting} + +The option \code{--help} is an alias for the \c{-h} option. + +The option \code{-hf} will also list the available output +file formats, and what they are. + +If you use Linux but aren't sure whether your system is +``a.out'' or ``ELF'', type + +\begin{lstlisting} +file nasm +\end{lstlisting} + +(in the directory in which you put the NASM binary when you +installed it). If it says something like + +\begin{lstlisting} +nasm: ELF 32-bit LSB executable i386 (386 and up) Version 1 +\end{lstlisting} + +then your system is ``ELF'', and you should use the option \code{-f elf} +when you want NASM to produce Linux object files. If it says + +\begin{lstlisting} +nasm: Linux/i386 demand-paged executable (QMAGIC) +\end{lstlisting} + +or something similar, your system is ``a.out'', and you should use +\code{-f aout} instead (Linux ``a.out'' systems have long been +obsolete, and are rare these days.) + +Like Unix compilers and assemblers, NASM is silent unless it +goes wrong: you won't see any output at all, unless it gives error +messages. + +\xsubsection{opt-o}{The \codeindex{-o} Option: Specifying the +\textindexlc{Output File Name}} + +NASM will normally choose the name of your output file for you; +precisely how it does this is dependent on the object file format. +For Microsoft object file formats (\code{obj}, \code{win32} +and \code{win64}), it will remove the ``.asm'' \textindex{extension} +(or whatever extension you like to use~-- NASM doesn't care) from your +source file name and substitute ``.obj''. For Unix object file formats +(\code{aout}, \code{as86}, \code{coff}, \code{elf32}, \code{elf64}, +\code{elfx32}, \code{ieee}, \code{macho32} and \code{macho64}) +it will substitute ``.o''. + +For \code{dbg}, \code{rdf}, \code{ith} and \code{srec}, it will use +``.dbg'', ``.rdf'', ``.ith'' and ``.srec'', respectively, and for +the \code{bin} format it will simply remove the extension, so that +``myfile.asm'' produces the output file ``myfile''. + +If the output file already exists, NASM will overwrite it, unless it +has the same name as the input file, in which case it will give a +warning and use ``\textindex{nasm.out}'' as the output +file name instead. + +For situations in which this behaviour is unacceptable, NASM +provides the \code{-o} command-line option, which allows you to +specify your desired output file name. You invoke \code{-o} by +following it with the name you wish for the output file, either +with or without an intervening space. For example: + +\begin{lstlisting} +nasm -f bin program.asm -o program.com +nasm -f bin driver.asm -o driver.sys +\end{lstlisting} + +Note that this is a small \code{-o}, and is different from a capital +\code{-O}, which is used to specify the number of optimisation passes +required. See \nref{opt-O}. + +\xsubsection{opt-f}{The \codeindex{-f} Option: Specifying the +\textindexlc{Output File Format}} + +If you do not supply the \code{-f} option to NASM, it will choose an +output file format for you itself. In the distribution versions of +NASM, the default is always \codeindex{bin}; if you've compiled +your own copy of NASM, you can redefine \codeindex{OF\_DEFAULT} +at compile time and choose what you want the default to be. + +Like \code{-o}, the intervening space between \code{-f} and the output +file format is optional; so \code{-f elf} and \code{-felf} are both valid. + +A complete list of the available output file formats can be given by +issuing the command \codeindex{nasm -hf}. + +\xsubsection{opt-l}{The \codeindex{-l} Option: Generating a \textindexlc{Listing File}} + +If you supply the \code{-l} option to NASM, followed (with the usual +optional space) by a file name, NASM will generate a \textindex{source-listing file} +for you, in which addresses and generated code are listed on the left, and the +actual source code, with expansions of multi-line macros (except those which +specifically request no expansion in source listings: see \nref{nolist}) +on the right. For example: + +\begin{lstlisting} +nasm -f elf myfile.asm -l myfile.lst +\end{lstlisting} + +If a list file is selected, you may turn off listing for a section of your +source with \code{[list -]}, and turn it back on with \code{[list +]}, +(the default, obviously). There is no ``user form'' (without the brackets). +This can be used to list only sections of interest, avoiding excessively +long listings. + +\xsubsection{opt-M}{The \codeindex{-M} Option: Generate +\textindexlc{Makefile Dependencies}} + +This option can be used to generate makefile dependencies on stdout. +This can be redirected to a file for further processing. For example: + +\begin{lstlisting} +nasm -M myfile.asm > myfile.dep +\end{lstlisting} + +\xsubsection{opt-MG}{The \codeindex{-MG} Option: Generate +\textindexlc{Makefile Dependencies}} + +This option can be used to generate makefile dependencies on stdout. +This differs from the \code{-M} option in that if a nonexisting file is +encountered, it is assumed to be a generated file and is added to the +dependency list without a prefix. + +\xsubsection{opt-MF}{The \codeindex{-MF} Option: Set Makefile Dependency File} + +This option can be used with the \code{-M} or \code{-MG} options +to send the output to a file, rather than to stdout. For example: + +\begin{lstlisting} +nasm -M -MF myfile.dep myfile.asm +\end{lstlisting} + +\xsubsection{opt-MD}{The \codeindex{-MD} Option: Assemble +and Generate Dependencies} + +The \code{-MD} option acts as the combination of the \code{-M} +and \code{-MF} options (i.e. a filename has to be specified). +However, unlike the \code{-M} or \code{-MG} options, \code{-MD} +does \emph{not} inhibit the normal operation of the assembler. +Use this to automatically generate updated dependencies with +every assembly session. For example: + +\begin{lstlisting} +nasm -f elf -o myfile.o -MD myfile.dep myfile.asm +\end{lstlisting} + +If the argument after \code{-MD} is an option rather than +a filename, then the output filename is the first applicable one of: + +\begin{itemize} + \item{the filename set in the \code{-MF} option;} + \item{the output filename from the \code{-o} option with \code{.d} appended;} + \item{the input filename with the extension set to \code{.d}.} +\end{itemize} + +\xsubsection{opt-MT}{The \codeindex{-MT} Option: +Dependency Target Name} + +The \code{-MT} option can be used to override the default name of the +dependency target. This is normally the same as the output filename, +specified by the \code{-o} option. + +\xsubsection{opt-MQ}{The \codeindex{-MQ} Option: +Dependency Target Name (Quoted)} + +The \code{-MQ} option acts as the \code{-MT} option, except +it tries to quote characters that have special meaning in Makefile +syntax. This is not foolproof, as not all characters with special +meaning are quotable in Make. The default output (if no \code{-MT} or +\code{-MQ} option is specified) is automatically quoted. + +\xsubsection{opt-MP}{The \codeindex{-MP} Option: +Emit phony targets} + +When used with any of the dependency generation options, the +\code{-MP} option causes NASM to emit a phony target without +dependencies for each header file. This prevents Make from +complaining if a header file has been removed. + +\xsubsection{opt-MW}{The \codeindex{-MW} Option: Watcom Make quoting style} + +This option causes NASM to attempt to quote dependencies according to +Watcom Make conventions rather than POSIX Make conventions (also used +by most other Make variants). This quotes \code{\#} as \code{\$\#} rather +than \code{\textbackslash\#}, uses \code{\&} rather than \code{\textbackslash} +for continuation lines, and encloses filenames containing whitespace in +double quotes. + +\xsubsection{opt-F}{The \codeindex{-F} Option: +Selecting a \textindexlc{Debug Information Format}} + +This option is used to select the format of the debug information +emitted into the output file, to be used by a debugger (or \emph{will} +be). Prior to version 2.03.01, the use of this switch did \emph{not} +enable output of the selected debug info format. Use \codeindex{-g}, +see \nref{opt-g}, to enable output. Versions 2.03.01 and later +automatically enable \code{-g} if \code{-F} is specified. + +A complete list of the available debug file formats for an output +format can be seen by issuing the command \code{nasm -f <format> -y}. +Not all output formats currently support debugging output. +See \nref{opt-y}. + +This should not be confused with the \code{-f dbg} output format option, +see \nref{dbgfmt}. + +\xsubsection{opt-g}{The \codeindex{-g} Option: +Enabling \textindexlc{Debug Information}} + +This option can be used to generate debugging information in the specified +format. See \nref{opt-F}. Using \code{-g} without \code{-F} +results in emitting debug info in the default format, if any, for the +selected output format. If no debug information is currently implemented +in the selected output format, \code{-g} is \emph{silently ignored}. + +\xsubsection{opt-X}{The \codeindex{-X} Option: +Selecting an \textindexlc{Error Reporting Format}} + +This option can be used to select an error reporting format for any +error messages that might be produced by NASM. + +Currently, two error reporting formats may be selected. They are +the \code{-Xvc} option and the \code{-Xgnu} option. +The GNU format is the default and looks like this: + +\begin{lstlisting} +filename.asm:65: error: specific error message +\end{lstlisting} + +where \code{filename.asm} is the name of the source file in +which the error was detected, \code{65} is the source file +line number on which the error was detected, \code{error} +is the severity of the error (this could be \code{warning}), +and \code{specific error message} is a more detailed text message +which should help pinpoint the exact problem. + +The other format, specified by \code{-Xvc} is the style used by +Microsoft Visual C++ and some other programs. It looks like this: + +\begin{lstlisting} +filename.asm(65) : error: specific error message +\end{lstlisting} + +where the only difference is that the line number is in parentheses +instead of being delimited by colons. + +See also the \code{Visual C++} output format, \nref{win32fmt}. + +\xsubsection{opt-Z}{The \codeindex{-Z} Option: +Send Errors to a File} + +Under ``MS-\textindex{DOS}'' it can be difficult (though there are +ways) to redirect the standard-error output of a program to a file. +Since NASM usually produces its warning and \textindex{error messages} +on \codeindex{stderr}, this can make it hard to capture the +errors if (for example) you want to load them into an editor. + +NASM therefore provides the \code{-Z} option, taking a filename argument +which causes errors to be sent to the specified files rather than standard +error. Therefore you can \index{redirecting errors}redirect the errors +into a file by typing + +\begin{lstlisting} +nasm -Z myfile.err -f obj myfile.asm +\end{lstlisting} + +In earlier versions of NASM, this option was called \code{-E}, +but it was changed since \code{-E} is an option conventionally +used for preprocessing only, with disastrous results. +See \nref{opt-E}. + +\xsubsection{opt-s}{The \codeindex{-s} Option: +Send Errors to \codeindex{stdout}} + +The \code{-s} option redirects \textindexlc{error messages} to +\code{stdout} rather than \code{stderr}, so it can be redirected +under ``MS-\textindex{DOS}''. To assemble the file \code{myfile.asm} +and pipe its output to the \code{more} program, you can type: + +\begin{lstlisting} +nasm -s -f obj myfile.asm | more +\end{lstlisting} + +See also the \code{-Z} option, \nref{opt-Z}. + +\xsubsection{opt-i}{The \codeindex{-i}\indexcode{-I} Option: +Include File Search Directories} + +When NASM sees the \codeindex{\%include} or \codeindex{\%pathsearch} directive +in a source file (see \nref{include}, \nref{pathsearch} or +\nref{incbin}), it will search for the given file not only in the +current directory, but also in any directories specified on the command +line by the use of the \code{-i} option. Therefore you can include files +from a \textindex{macro library}, for example, by typing + +\begin{lstlisting} +nasm -ic:\macrolib\ -f obj myfile.asm +\end{lstlisting} + +(As usual, a space between \code{-i} and the path name is allowed, and +optional). + +Prior NASM 2.14 a path provided in the option has been considered as +a verbatim copy and providing a path separator been up to a caller. +One could implicitly concatenate a search path together with a filename. +Still this was rather a trick than something useful. Now the trailing +path separator is made to always present, thus \code{-ifoo} will be +considered as the \code{-ifoo/} directory. + +If you want to define a \emph{standard} \textindex{include search path}, +similar to \code{/usr/include} on Unix systems, you should place one or +more \code{-i} directives in the \code{NASMENV} environment variable (see +\nref{nasmenv}). + +For Makefile compatibility with many C compilers, this option can also +be specified as \code{-I}. + +\xsubsection{opt-p}{The \codeindex{-p}\indexcode{-P} Option: +Pre-Include a File} +\index{pre-including files} + +\indexcode{\%include}NASM allows you to specify files to be \emph{pre-included} into +your source file, by the use of the \code{-p} option. So running + +\begin{lstlisting} +nasm myfile.asm -p myinc.inc +\end{lstlisting} + +is equivalent to running \code{nasm myfile.asm} and placing the +directive \code{\%include "myinc.inc"} at the start of the file. + +\code{--include} option is also accepted. + +For consistency with the \code{-I}, \code{-D} and \code{-U} options, +this option can also be specified as \code{-P}. + +\xsubsection{opt-d}{The \codeindex{-d}\indexcode{-D} Option: +Pre-Define a Macro} +\index{pre-defining macros} + +\indexcode{\%define}Just as the \code{-p} option gives an alternative to placing +\code{\%include} directives at the start of a source file, the \code{-d} +option gives an alternative to placing a \code{\%define} directive. You +could code + +\begin{lstlisting} +nasm myfile.asm -dFOO=100 +\end{lstlisting} + +as an alternative to placing the directive + +\begin{lstlisting} +%define FOO 100 +\end{lstlisting} + +at the start of the file. You can miss off the macro value, as well: +the option \code{-dFOO} is equivalent to coding \code{\%define FOO}. +This form of the directive may be useful for selecting \textindex{assembly-time +options} which are then tested using \code{\%ifdef}, for example \code{-dDEBUG}. + +For Makefile compatibility with many C compilers, this option can also +be specified as \code{-D}. + +\xsubsection{opt-u}{The \codeindex{-u}\indexcode{-U} Option: +Undefine a Macro} +\index{undefining macros} + +\indexcode{\%undef}The \code{-u} option undefines a macro that would otherwise +have been pre-defined, either automatically or by a \code{-p} or \code{-d} +option specified earlier on the command lines. + +For example, the following command line: + +\begin{lstlisting} +nasm myfile.asm -dFOO=100 -uFOO +\end{lstlisting} + +would result in \code{FOO} \emph{not} being a predefined macro in the +program. This is useful to override options specified at a different +point in a Makefile. + +For Makefile compatibility with many C compilers, this option can also +be specified as \code{-U}. + +\xsubsection{opt-E}{The \codeindex{-E}\indexcode{-e} Option: Preprocess Only} + +NASM allows the \textindex{preprocessor} to be run on its own, up to a +point. Using the \code{-E} option (which requires no arguments) will +cause NASM to preprocess its input file, expand all the macro references, +remove all the comments and preprocessor directives, and print the resulting +file on standard output (or save it to a file, if the \code{-o} option +is also used). + +This option cannot be applied to programs which require the +preprocessor to evaluate \index{preprocessor expressions} +\textindex{expressions} which depend on the values of symbols: +so code such as + +\begin{lstlisting} +%assign tablesize ($-tablestart) +\end{lstlisting} + +will cause an error in \textindex{preprocess-only mode}. + +For compatiblity with older version of NASM, this option can also be +written \code{-e}. \code{-E} in older versions of NASM was the equivalent +of the current \code{-Z} option, \nref{opt-Z}. + +\xsubsection{opt-a}{The \codeindex{-a} Option: Don't Preprocess At All} + +If NASM is being used as the back end to a compiler, it might be +desirable to \index{suppressing preprocessing}suppress preprocessing +completely and assume the compiler has already done it, to save time +and increase compilation speeds. The \code{-a} option, requiring no +argument, instructs NASM to replace its powerful \textindex{preprocessor} +with a \textindex{stub preprocessor} which does nothing. + +\xsubsection{opt-O}{The \codeindex{-O} Option: Specifying +\textindexlc{Multipass Optimization}} + +Using the \code{-O} option, you can tell NASM to carry out different +levels of optimization. Multiple flags can be specified after the +\code{-O} options, some of which can be combined in a single option, +e.g. \code{-Oxv}. + +\begin{itemize} + \item{\code{-O0}: No optimization. All operands take their + long forms, if a short form is not specified, except conditional + jumps. This is intended to match NASM 0.98 behavior.} + + \item{\code{-O1}: Minimal optimization. As above, but immediate + operands which will fit in a signed byte are optimized, + unless the long form is specified. Conditional jumps default + to the long form unless otherwise specified.} + + \item{\code{-Ox} (where \code{x} is the actual letter \code{x}): + Multipass optimization. Minimize branch offsets and signed immediate + bytes, overriding size specification unless the \code{strict} keyword + has been used (see \nref{strict}). For compatibility with earlier + releases, the letter \code{x} may also be any number greater than + one. This number has no effect on the actual number of passes.} + + \item{\code{-Ov}: At the end of assembly, print the number of passes + actually executed.} +\end{itemize} + +The \code{-Ox} mode is recommended for most uses, and is the default +since NASM 2.09. + +Note that this is a capital \code{O}, and is different from a small \code{o}, +which is used to specify the output file name. See \nref{opt-o}. + +\xsubsection{opt-t}{The \codeindex{-t} Option: Enable TASM Compatibility Mode} + +NASM includes a limited form of compatibility with Borland's \textindex{TASM}. +When NASM's \code{-t} option is used, the following changes are made: + +\begin{itemize} + \item{local labels may be prefixed with \code{@@} instead of \code{.};} + + \item{size override is supported within brackets. In TASM compatible mode, + a size override inside square brackets changes the size of the operand, + and not the address type of the operand as it does in NASM syntax. E.g. + \code{mov eax,[DWORD val]} is valid syntax in TASM compatibility mode. + Note that you lose the ability to override the default address type for + the instruction;} + + \item{unprefixed forms of some directives supported (\code{arg}, \code{elif}, + \code{else}, \code{endif}, \code{if}, \code{ifdef}, \code{ifdifi}, + \code{ifndef}, \code{include}, \code{local}).} +\end{itemize} + +\xsubsection{opt-w}{The \codeindex{-w} and \codeindex{-W} Options: +Enable or Disable Assembly \textindexlc{Warnings}} + +NASM can observe many conditions during the course of assembly which +are worth mentioning to the user, but not a sufficiently severe +error to justify NASM refusing to generate an output file. These +conditions are reported like errors, but come up with the word +``warning'' before the message. Warnings do not prevent NASM from +generating an output file and returning a success status to the +operating system. + +Some conditions are even less severe than that: they are only +sometimes worth mentioning to the user. Therefore NASM supports the +\code{-w} command-line option, which enables or disables certain +classes of assembly warning. Such warning classes are described by a +name, for example \code{orphan-labels}; you can enable warnings of +this class by the command-line option \code{-w+orphan-labels} and +disable it by \code{-w-orphan-labels}. + +The current \textindex{warning classes} are: +\begin{itemize} + + \item \codeindex{other} specifies any warning not otherwise + specified in any class. Enabled by default. + + \item \codeindex{macro-params} covers warnings about + \textindex{multi-line macros} being invoked with the wrong number + of parameters. Enabled by default, see \nref{mlmacover} + for an example of why you might want to disable it. + + \item \codeindex{macro-selfref} warns if a macro references itself. + Disabled by default. + + \item \codeindex{macro-defaults} warns when a macro has more + default parameters than optional parameters. Enabled by default, + see \nref{mlmacdef} for why you might want to disable it. + + \item \codeindex{orphan-labels} covers warnings about source lines + which contain no instruction but define a label without a trailing colon. + NASM warns about this somewhat obscure condition by default, + see \nref{syntax} for more information. + + \item \codeindex{number-overflow} covers warnings about numeric + constants which don't fit in 64 bits. Enabled by default. + + \item \codeindex{gnu-elf-extensions} warns if 8-bit or 16-bit + relocations are used in \code{-f elf} format. The GNU extensions + allow this. Disabled by default. + + \item \codeindex{float-overflow} warns about floating point overflow. + Enabled by default. + + \item \codeindex{float-denorm} warns about floating point denormals. + Disabled by default. + + \item \codeindex{float-underflow} warns about floating point underflow. + Disabled by default. + + \item \codeindex{float-toolong} warns about too many digits in + floating-point numbers. Enabled by default. + + \item \codeindex{user} controls \code{\%warning} directives (see + \nref{pperror}). Enabled by default. + + \item \codeindex{lock} warns about \code{LOCK} prefixes on unlockable + instructions. Enabled by default. + + \item \codeindex{hle} warns about invalid use of the HLE \code{XACQUIRE} + or \code{XRELEASE} prefixes. Enabled by default. + + \item \codeindex{bnd} warns about ineffective use of the \code{BND} + prefix when a relaxed form of jmp instruction becomes jmp short form. + Enabled by default. + + \item \codeindex{zext-reloc} warns that a relocation has been + zero-extended due to limitations in the output format. Enabled by default. + + \item \codeindex{ptr} warns about keywords used in other assemblers that might + indicate a mistake in the source code. Currently only the MASM + \code{PTR} keyword is recognized. Enabled by default. + + \item \codeindex{bad-pragma} warns about a malformed or otherwise unparsable + \code{\%pragma} directive. Disabled by default. + + \item \codeindex{unknown-pragma} warns about an unknown \code{\%pragma} directive. + This is not yet implemented. Disabled by default. + + \item \codeindex{not-my-pragma} warns about a \code{\%pragma} directive which is + not applicable to this particular assembly session. This is not yet + implemented. Disabled by default. + + \item \codeindex{unknown-warning} warns about a \code{-w} or \code{-W} option or a + \code{[WARNING]} directive that contains an unknown warning name or is + otherwise not possible to process. Disabled by default. + + \item \codeindex{all} is an alias for \emph{all} suppressible warning classes. + Thus, \code{-w+all} enables all available warnings, and \code{-w-all} + disables warnings entirely (since NASM 2.13). +\end{itemize} + +Since version 2.00, NASM has also supported the \code{gcc}-like syntax +\code{-Wwarning-class} and \code{-Wno-warning-class} instead of +\code{-w+warning-class} and \code{-w-warning-class}, respectively; both +syntaxes work identically. + +The option \code{-w+error} or \codeindex{-Werror} can be used to treat warnings +as errors. This can be controlled on a per warning class basis +(\code{-w+error=}\emph{warning-class} or \code{-Werror=}\emph{warning-class}); +if no \emph{warning-class} is specified NASM treats it as +\code{-w+error=all}; the same applies to \code{-w-error} or +\codeindex{-Wno-error}, of course. + +In addition, you can control warnings in the source code itself, using +the \codeindex{[WARNING]} directive. See \nref{asmdir-warning}. + +\xsubsection{opt-v}{The \codeindex{-v} Option: Display \textindexlc{Version} Info} + +Typing \code{NASM -v} will display the version of NASM which you are using, +and the date on which it was compiled. + +You will need the version number if you report a bug. + +For command-line compatibility with Yasm, the form \codeindex{--v} is also +accepted for this option starting in NASM version 2.11.05. + +\xsubsection{opt-y}{The \codeindex{-y} Option: Display Available Debug Info Formats} + +Typing \code{nasm -f <option> -y} will display a list of the available +debug info formats for the given output format. The default format +is indicated by an asterisk. For example: + +\begin{lstlisting} +nasm -f elf -y + +valid debug formats for 'elf32' output format are +('*' denotes default): +* stabs ELF32 (i386) stabs debug format for Linux + dwarf elf32 (i386) dwarf debug format for Linux +\end{lstlisting} + +\xsubsection{opt-pfix}{The \codeindex{--(g|l)prefix}, \codeindex{--(g|l)postfix} Options} + +The \code{--(g)prefix} options prepend the given argument +to all \code{extern}, \code{common}, \code{static}, and +\code{global} symbols, and the \code{--lprefix} option prepends +to all other symbols. Similarly, \code{--(g)postfix} and \code{--lpostfix} +options append the argument in the exactly same way as the \code{--xxprefix} +options does. + +Running this: + +\begin{lstlisting} +nasm -f macho --gprefix _ +\end{lstlisting} + +is equivalent to place the directive with \code{\%pragma macho gprefix \_} +at the start of the file (\nref{mangling}). It will prepend the underscore +to all global and external variables, as C requires it in some, but not all, +system calling conventions. + +\xsubsection{opt-pragma}{The \codeindex{--pragma} Option} + +NASM accepts an argument as \code{\%pragma} option, which is like placing +a \code{\%pragma} preprocess statement at the beginning of the source. +Running this: + +\begin{lstlisting} +nasm -f macho --pragma "macho gprefix _" +\end{lstlisting} + +is equivalent to the example in \nref{opt-pfix}. + +\xsubsection{opt-before}{The \codeindex{--before} Option} + +A preprocess statement can be accepted with this option. The example +shown in \nref{opt-pragma} is the same as running this: + +\begin{lstlisting} +nasm -f macho --before "%pragma macho gprefix _" +\end{lstlisting} + +\xsubsection{opt-limit}{The \codeindex{--limit-X} Option} + +This option allows user to setup various maximum values for these: + +\begin{itemize} + \item{\code{--limit-passes}: Number of maximum allowed passes. Default is + effectively unlimited.} + + \item{\code{--limit-stalled-passes}: Maximum number of allowed unfinished + passes. Default is 1000.} + + \item{\code{--limit-macro-levels}: Define maximum depth of macro expansion + (in preprocess). Default is 1000000.} + + \item{\code{--limit-rep}: Maximum number of allowed preprocessor loop, defined + under \code{\%rep}. Default is 1000000.} + + \item{\code{--limit-eval}: This number sets the boundary condition of allowed + expression length. Default is 1000000.} + + \item{\code{--limit-lines}: Total number of source lines as allowed to be + processed. Default is 2000000000.} +\end{itemize} + +In example, running this limits the maximum line count to be 1000. + +\begin{lstlisting} +nasm --limit-lines 1000 +\end{lstlisting} + +\xsubsection{opt-keep-all}{The \codeindex{--keep-all} Option} + +This option prevents NASM from deleting any output files even if an +error happens. + +\xsubsection{opt-no-line}{The \codeindex{--no-line} Option} + +If this option is given, all \codeindex{\%line} directives in the source code +are ignored. This can be useful for debugging already preprocessed +code. See \nref{line}. + +\xsubsection{nasmenv}{The \codeindex{NASMENV} \textindex{Environment} Variable} + +If you define an environment variable called \code{NASMENV}, the program +will interpret it as a list of extra command-line options, which are +processed before the real command line. You can use this to define +standard search directories for include files, by putting \code{-i} +options in the \code{NASMENV} variable. + +The value of the variable is split up at white space, so that the +value \code{-s -ic:\textbackslash nasmlib\textbackslash} will be +treated as two separate options. However, that means that the value +\code{-dNAME="my name"} won't do what you might want, because it +will be split at the space and the NASM command-line processing +will get confused by the two nonsensical words \code{-dNAME="my} +and \code{name"}. + +To get round this, NASM provides a feature whereby, if you begin the +\code{NASMENV} environment variable with some character that isn't +a minus sign, then NASM will treat this character as the +\textindex{separator character} for options. So setting the \code{NASMENV} +variable to the value \code{!-s!-ic:\textbackslash nasmlib\textbackslash} +is equivalent to setting it to \code{-s -ic:\textbackslash nasmlib\textbackslash}, +but \code{!-dNAME="my name"} will work. + +This environment variable was previously called \code{NASM}. This was +changed with version 0.98.31. + +\xsection{qstart}{\textindex{Quick Start} for \textindex{MASM} Users} + +If you're used to writing programs with MASM, or with \textindex{TASM} in +MASM-compatible (non-Ideal) mode, or with \textindex{a86}, this section +attempts to outline the major differences between MASM's syntax and +NASM's. If you're not already used to MASM, it's probably worth +skipping this section. + +\xsubsection{qscs}{NASM Is \index{case sensitivity}Case-Sensitive} + +One simple difference is that NASM is case-sensitive. It makes a +difference whether you call your label \code{foo}, \code{Foo} or +\code{FOO}. If you're assembling to DOS or OS/2 ``.OBJ'' files, +you can invoke the \codeindex{UPPERCASE} directive (documented in +\nref{objfmt}) to ensure that all symbols exported to other +code modules are forced to be upper case; but even then, \emph{within} +a single module, NASM will distinguish between labels differing only +in case. + +\xsubsection{qsbrackets}{NASM Requires \textindexlc{Square Brackets} +For \textindexlc{Memory References}} + +NASM was designed with simplicity of syntax in mind. One of the +\textindex{design goals} of NASM is that it should be possible, +as far as is practical, for the user to look at a single line of +NASM code and tell what opcode is generated by it. You can't do +this in MASM: if you declare, for example, + +\begin{lstlisting} +foo equ 1 +bar dw 2 +\end{lstlisting} + +then the two lines of code + +\begin{lstlisting} +mov ax,foo +mov ax,bar +\end{lstlisting} + +generate completely different opcodes, despite having +identical-looking syntaxes. + +NASM avoids this undesirable situation by having a much simpler +syntax for memory references. The rule is simply that any access to +the \emph{contents} of a memory location requires square brackets +around the address, and any access to the \emph{address} of a variable +doesn't. So an instruction of the form \code{mov ax,foo} will +\emph{always} refer to a compile-time constant, whether it's an \code{EQU} +or the address of a variable; and to access the \emph{contents} of the +variable \code{bar}, you must code \code{mov ax,[bar]}. + +This also means that NASM has no need for MASM's \codeindex{OFFSET} +keyword, since the MASM code \code{mov ax,offset bar} means exactly the +same thing as NASM's \code{mov ax,bar}. If you're trying to get +large amounts of MASM code to assemble sensibly under NASM, you +can always code \code{\%idefine offset} to make the preprocessor +treat the \code{OFFSET} keyword as a no-op. + +This issue is even more confusing in \textindex{a86}, where declaring a +label with a trailing colon defines it to be a `label' as opposed to +a `variable' and causes a86 to adopt NASM-style semantics; so in +a86, \code{mov ax,var} has different behaviour depending on whether +\code{var} was declared as \code{var: dw 0} (a label) or +\code{var dw 0} (a word-size variable). NASM is very simple by +comparison: \emph{everything} is a label. + +NASM, in the interests of simplicity, also does not support the +\textindex{hybrid syntaxes} supported by MASM and its clones, such as +\code{mov ax,table[bx]}, where a memory reference is denoted by one +portion outside square brackets and another portion inside. The +correct syntax for the above is \code{mov ax,[table+bx]}. Likewise, +\code{mov ax,es:[di]} is wrong and \code{mov ax,[es:di]} is right. + +\xsubsection{qstypes}{NASM Doesn't Store \textindexlc{Variable Types}} + +NASM, by design, chooses not to remember the types of variables you +declare. Whereas MASM will remember, on seeing \code{var dw 0}, that +you declared \code{var} as a word-size variable, and will then be able +to fill in the \textindex{ambiguity} in the size of the instruction +\code{mov var,2}, NASM will deliberately remember nothing about +the symbol \code{var} except where it begins, and so you must +explicitly code \code{mov word [var],2}. + +For this reason, NASM doesn't support the \code{LODS}, \code{MOVS}, +\code{STOS}, \code{SCAS}, \code{CMPS}, \code{INS}, or \code{OUTS} +instructions, but only supports the forms such as \code{LODSB}, +\code{MOVSW}, and \code{SCASD}, which explicitly specify the size +of the components of the strings being manipulated. + +\xsubsection{qsassume}{NASM Doesn't \codeindex{ASSUME}} + +As part of NASM's drive for simplicity, it also does not support the +\code{ASSUME} directive. NASM will not keep track of what values you +choose to put in your segment registers, and will never \emph{automatically} +generate a \textindex{segment override} prefix. + +\xsubsection{qsmodel}{NASM Doesn't Support \textindexlc{Memory Models}} + +NASM also does not have any directives to support different 16-bit +memory models. The programmer has to keep track of which functions +are supposed to be called with a \textindex{far call} and which with a +\textindex{near call}, and is responsible for putting the correct form of +\code{RET} instruction (\code{RETN} or \code{RETF}; NASM accepts +\code{RET} itself as an alternate form for \code{RETN}); in addition, +the programmer is responsible for coding CALL FAR instructions where +necessary when calling \emph{external} functions, and must also keep +track of which external variable definitions are far and which are +near. + +\xsubsection{qsfpu}{\textindexlc{Floating-Point} Differences} + +NASM uses different names to refer to floating-point registers from +MASM: where MASM would call them \code{ST(0)}, \code{ST(1)} and +so on, and \textindex{a86} would call them simply \code{0}, \code{1} +and so on, NASM chooses to call them \code{st0}, \code{st1} etc. + +As of version 0.96, NASM now treats the instructions with +`\textindex{nowait}' forms in the same way as MASM-compatible assemblers. +The idiosyncratic treatment employed by 0.95 and earlier was based +on a misunderstanding by the authors. + +\xsubsection{qsother}{Other Differences} + +For historical reasons, NASM uses the keyword \codeindex{TWORD} where +MASM and compatible assemblers use \codeindex{TBYTE}. + +NASM does not declare \textindex{uninitialized storage} in the same way +as MASM: where a MASM programmer might use \code{stack db 64 dup (?)}, +NASM requires \code{stack resb 64}, intended to be read as \emph{reserve 64 +bytes}. For a limited amount of compatibility, since NASM treats +\code{?} as a valid character in symbol names, you can code \code{? equ 0} +and then writing \code{dw ?} will at least do something vaguely useful. +\index{RESB}\codeindex{DUP} is still not a supported syntax, however. + +In addition to all of this, macros and directives work completely +differently to MASM. See \nref{preproc} and \nref{directive} +for further details. diff --git a/doc/latex/src/source.tex b/doc/latex/src/source.tex new file mode 100644 index 00000000..32323f76 --- /dev/null +++ b/doc/latex/src/source.tex @@ -0,0 +1,53 @@ +% +% vim: ts=4 sw=4 et +% +\xchapter{source}{Building NASM from Source} + +The source code for NASM is available from our website, +\href{http://www.nasm.us/}{http://wwww.nasm.us/}, +see \nref{website}. + +\xsection{tarball}{Building from a Source Archive} + +The source archives available on the web site should be capable of +building on a number of platforms. This is the recommended method for +building NASM to support platforms for which executables are not +available. + +On a system which has Unix shell (\code{sh}), run: + +\begin{lstlisting} +sh configure +make everything +\end{lstlisting} + +A number of options can be passed to \code{configure}; see +\code{sh configure --help}. + +A set of Makefiles for some other environments are also available; +please see the file \code{Mkfiles/README}. + +To build the installer for the Windows platform, you will need the +Nullsoft Scriptable Installer, \textindex{NSIS}, installed. + +To build the documentation, you will need a set of additional tools. +The documentation is not likely to be able to build on non-Unix +systems. + +\xsection{git}{Building from the \codeindex{git} Repository} + +The NASM development tree is kept in a source code repository using +the \code{git} distributed source control system. The link is available +on the website. This is recommended only to participate in the +development of NASM or to assist with testing the development code. + +To build NASM from the \code{git} repository you will need a Perl and, if +building on a Unix system, GNU autoconf. + +To build on a Unix system, run: + +\begin{lstlisting} +sh autogen.sh +\end{lstlisting} + +to create the \code{configure} script and then build as listed above. diff --git a/doc/latex/src/trouble.tex b/doc/latex/src/trouble.tex new file mode 100644 index 00000000..b129780f --- /dev/null +++ b/doc/latex/src/trouble.tex @@ -0,0 +1,114 @@ +% +% vim: ts=4 sw=4 et +% +\xchapter{trouble}{Troubleshooting} + +This chapter describes some of the common problems that users have +been known to encounter with NASM, and answers them. If you think you +have found a bug in NASM, please see \nref{bugs}. + +\xsection{problems}{Common Problems} + +\xsubsection{inefficient}{NASM Generates \textindexlc{Inefficient Code}} + +We sometimes get `bug' reports about NASM generating inefficient, or +even `wrong', code on instructions such as \code{ADD ESP,8}. This is a +deliberate design feature, connected to predictability of output: +NASM, on seeing \code{ADD ESP,8}, will generate the form of the +instruction which leaves room for a 32-bit offset. You need to code +\indexcode{BYTE}\code{ADD ESP,BYTE 8} if you want the space-efficient +form of the instruction. This isn't a bug, it's user error: if you +prefer to have NASM produce the more efficient code automatically enable +optimization with the \code{-O} option (see \nref{opt-O}). + +\xsubsection{jmprange}{My Jumps are Out of Range} +\index{out of range!jumps} + +Similarly, people complain that when they issue \textindex{conditional +jumps} (which are \code{SHORT} by default) that try to jump too far, +NASM reports `short jump out of range' instead of making the jumps +longer. + +This, again, is partly a predictability issue, but in fact has a +more practical reason as well. NASM has no means of being told what +type of processor the code it is generating will be run on; so it +cannot decide for itself that it should generate \codeindex{Jcc NEAR} +type instructions, because it doesn't know that it's working for a 386 or +above. Alternatively, it could replace the out-of-range short +\code{JNE} instruction with a very short \code{JE} instruction that jumps +over a \code{JMP NEAR}; this is a sensible solution for processors +below a 386, but hardly efficient on processors which have good +branch prediction \emph{and} could have used \code{JNE NEAR} instead. So, +once again, it's up to the user, not the assembler, to decide what +instructions should be generated. See \nref{opt-O}. + +\xsubsection{proborg}{\codeindex{ORG} Doesn't Work} + +People writing \textindex{boot sector} programs in the \code{bin} format often +complain that \code{ORG} doesn't work the way they'd like: in order to +place the \code{0xAA55} signature word at the end of a 512-byte boot +sector, people who are used to MASM tend to code + +\begin{lstlisting} + ORG 0 + + ; some boot sector code + + ORG 510 + DW 0xAA55 +\end{lstlisting} + +This is not the intended use of the \code{ORG} directive in NASM, and +will not work. The correct way to solve this problem in NASM is to +use the \codeindex{TIMES} directive, like this: + +\begin{lstlisting} + ORG 0 + + ; some boot sector code + + TIMES 510-($-$$) DB 0 + DW 0xAA55 +\end{lstlisting} + +The \code{TIMES} directive will insert exactly enough zero bytes into +the output to move the assembly point up to 510. This method also +has the advantage that if you accidentally fill your boot sector too +full, NASM will catch the problem at assembly time and report it, so +you won't end up with a boot sector that you have to disassemble to +find out what's wrong with it. + +\xsubsection{probtimes}{\codeindex{TIMES} Doesn't Work} + +The other common problem with the above code is people who write the +\code{TIMES} line as + +\begin{lstlisting} + TIMES 510-$ DB 0 +\end{lstlisting} + +by reasoning that \code{\$} should be a pure number, just like 510, so +the difference between them is also a pure number and can happily be +fed to \code{TIMES}. + +NASM is a \emph{modular} assembler: the various component parts are +designed to be easily separable for re-use, so they don't exchange +information unnecessarily. In consequence, the \code{bin} output +format, even though it has been told by the \code{ORG} directive that +the \code{.text} section should start at 0, does not pass that +information back to the expression evaluator. So from the +evaluator's point of view, \code{\$} isn't a pure number: it's an offset +from a section base. Therefore the difference between \code{\$} and 510 +is also not a pure number, but involves a section base. Values +involving section bases cannot be passed as arguments to \code{TIMES}. + +The solution, as in the previous section, is to code the \code{TIMES} +line in the form + +\begin{lstlisting} + TIMES 510-($-$$) DB 0 +\end{lstlisting} + +in which \code{\$} and \code{\$\$} are offsets from the same section base, +and so their difference is a pure number. This will solve the +problem and generate sensible code. diff --git a/doc/latex/src/version.tex b/doc/latex/src/version.tex new file mode 100644 index 00000000..607821ae --- /dev/null +++ b/doc/latex/src/version.tex @@ -0,0 +1,4 @@ +% +% vim: ts=4 sw=4 et +% +\newcommand{\version}{2.14.01-272-gb3f7c8eb} |