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author | jsm28 <jsm28@138bc75d-0d04-0410-961f-82ee72b054a4> | 2001-11-11 11:31:24 +0000 |
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committer | jsm28 <jsm28@138bc75d-0d04-0410-961f-82ee72b054a4> | 2001-11-11 11:31:24 +0000 |
commit | 38d07189cc68f42f8eb2d9d2fbd982a67cae19b3 (patch) | |
tree | fb11a0a4586ddc121bcbc19d21bd432eb1b5ed34 /gcc/doc/gcc.texi | |
parent | 4a82352a84766c06cff20385665f3f3828163a19 (diff) | |
download | gcc-38d07189cc68f42f8eb2d9d2fbd982a67cae19b3.tar.gz |
* doc/gcc.texi: Move several chapters out to ...
* doc/bugreport.texi, doc/contribute.texi, doc/frontends.texi,
doc/service.texi, doc/standards.texi, doc/trouble.texi,
doc/vms.texi: ... here. New files.
* Makefile.in ($(docdir)/gcc.info, gcc.dvi): Update dependencies.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@46929 138bc75d-0d04-0410-961f-82ee72b054a4
Diffstat (limited to 'gcc/doc/gcc.texi')
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1 files changed, 9 insertions, 2456 deletions
diff --git a/gcc/doc/gcc.texi b/gcc/doc/gcc.texi index f476d8d1faf..43301abf567 100644 --- a/gcc/doc/gcc.texi +++ b/gcc/doc/gcc.texi @@ -277,242 +277,10 @@ bugs. It corresponds to GCC version 3.1. @end menu @ifset USING -@node G++ and GCC -@chapter Compile C, C++, Objective-C, Ada, CHILL, Fortran, or Java - -@cindex Objective-C -@cindex Fortran -@cindex Java -@cindex CHILL -@cindex Ada -Several versions of the compiler (C, C++, Objective-C, Ada, CHILL, -Fortran, and Java) are integrated; this is why we use the name -``GNU Compiler Collection''. GCC can compile programs written in any of these -languages. The Ada, CHILL, Fortran, and Java compilers are described in -separate manuals. - -@cindex GCC -``GCC'' is a common shorthand term for the GNU Compiler Collection. This is both -the most general name for the compiler, and the name used when the -emphasis is on compiling C programs (as the abbreviation formerly -stood for ``GNU C Compiler''). - -@cindex C++ -@cindex G++ -When referring to C++ compilation, it is usual to call the compiler -``G++''. Since there is only one compiler, it is also accurate to call -it ``GCC'' no matter what the language context; however, the term -``G++'' is more useful when the emphasis is on compiling C++ programs. - -@cindex Ada -@cindex GNAT -Similarly, when we talk about Ada compilation, we usually call the -compiler ``GNAT'', for the same reasons. - -We use the name ``GCC'' to refer to the compilation system as a -whole, and more specifically to the language-independent part of the -compiler. For example, we refer to the optimization options as -affecting the behavior of ``GCC'' or sometimes just ``the compiler''. - -Front ends for other languages, such as Mercury and Pascal exist but -have not yet been integrated into GCC@. These front ends, like that for C++, -are built in subdirectories of GCC and link to it. The result is an -integrated compiler that can compile programs written in C, C++, -Objective-C, or any of the languages for which you have installed front -ends. - -In this manual, we only discuss the options for the C, Objective-C, and -C++ compilers and those of the GCC core. Consult the documentation -of the other front ends for the options to use when compiling programs -written in other languages. - -@cindex compiler compared to C++ preprocessor -@cindex intermediate C version, nonexistent -@cindex C intermediate output, nonexistent -G++ is a @emph{compiler}, not merely a preprocessor. G++ builds object -code directly from your C++ program source. There is no intermediate C -version of the program. (By contrast, for example, some other -implementations use a program that generates a C program from your C++ -source.) Avoiding an intermediate C representation of the program means -that you get better object code, and better debugging information. The -GNU debugger, GDB, works with this information in the object code to -give you comprehensive C++ source-level editing capabilities -(@pxref{C,,C and C++,gdb.info, Debugging with GDB}). - -@c FIXME! Someone who knows something about Objective-C ought to put in -@c a paragraph or two about it here, and move the index entry down when -@c there is more to point to than the general mention in the 1st par. - -@node Standards -@chapter Language Standards Supported by GCC -@cindex C standard -@cindex C standards -@cindex ANSI C standard -@cindex ANSI C -@cindex ANSI C89 -@cindex C89 -@cindex ANSI X3.159-1989 -@cindex X3.159-1989 -@cindex ISO C standard -@cindex ISO C -@cindex ISO C89 -@cindex ISO C90 -@cindex ISO/IEC 9899 -@cindex ISO 9899 -@cindex C90 -@cindex ISO C94 -@cindex C94 -@cindex ISO C95 -@cindex C95 -@cindex ISO C99 -@cindex C99 -@cindex ISO C9X -@cindex C9X -@cindex Technical Corrigenda -@cindex TC1 -@cindex Technical Corrigendum 1 -@cindex TC2 -@cindex Technical Corrigendum 2 -@cindex AMD1 -@cindex freestanding implementation -@cindex freestanding environment -@cindex hosted implementation -@cindex hosted environment -@findex __STDC_HOSTED__ - -For each language compiled by GCC for which there is a standard, GCC -attempts to follow one or more versions of that standard, possibly -with some exceptions, and possibly with some extensions. - -GCC supports three versions of the C standard, although support for -the most recent version is not yet complete. - -@opindex std -@opindex ansi -@opindex pedantic -@opindex pedantic-errors -The original ANSI C standard (X3.159-1989) was ratified in 1989 and -published in 1990. This standard was ratified as an ISO standard -(ISO/IEC 9899:1990) later in 1990. There were no technical -differences between these publications, although the sections of the -ANSI standard were renumbered and became clauses in the ISO standard. -This standard, in both its forms, is commonly known as @dfn{C89}, or -occasionally as @dfn{C90}, from the dates of ratification. The ANSI -standard, but not the ISO standard, also came with a Rationale -document. To select this standard in GCC, use one of the options -@option{-ansi}, @option{-std=c89} or @option{-std=iso9899:1990}; to obtain -all the diagnostics required by the standard, you should also specify -@option{-pedantic} (or @option{-pedantic-errors} if you want them to be -errors rather than warnings). @xref{C Dialect Options,,Options -Controlling C Dialect}. - -Errors in the 1990 ISO C standard were corrected in two Technical -Corrigenda published in 1994 and 1996. GCC does not support the -uncorrected version. - -An amendment to the 1990 standard was published in 1995. This -amendment added digraphs and @code{__STDC_VERSION__} to the language, -but otherwise concerned the library. This amendment is commonly known -as @dfn{AMD1}; the amended standard is sometimes known as @dfn{C94} or -@dfn{C95}. To select this standard in GCC, use the option -@option{-std=iso9899:199409} (with, as for other standard versions, -@option{-pedantic} to receive all required diagnostics). - -A new edition of the ISO C standard was published in 1999 as ISO/IEC -9899:1999, and is commonly known as @dfn{C99}. GCC has incomplete -support for this standard version; see -@uref{http://gcc.gnu.org/c99status.html} for details. To select this -standard, use @option{-std=c99} or @option{-std=iso9899:1999}. (While in -development, drafts of this standard version were referred to as -@dfn{C9X}.) - -@opindex traditional -GCC also has some limited support for traditional (pre-ISO) C with the -@option{-traditional} option. This support may be of use for compiling -some very old programs that have not been updated to ISO C, but should -not be used for new programs. It will not work with some modern C -libraries such as the GNU C library. - -By default, GCC provides some extensions to the C language that on -rare occasions conflict with the C standard. @xref{C -Extensions,,Extensions to the C Language Family}. Use of the -@option{-std} options listed above will disable these extensions where -they conflict with the C standard version selected. You may also -select an extended version of the C language explicitly with -@option{-std=gnu89} (for C89 with GNU extensions) or @option{-std=gnu99} -(for C99 with GNU extensions). The default, if no C language dialect -options are given, is @option{-std=gnu89}; this will change to -@option{-std=gnu99} in some future release when the C99 support is -complete. Some features that are part of the C99 standard are -accepted as extensions in C89 mode. - -The ISO C standard defines (in clause 4) two classes of conforming -implementation. A @dfn{conforming hosted implementation} supports the -whole standard including all the library facilities; a @dfn{conforming -freestanding implementation} is only required to provide certain -library facilities: those in @code{<float.h>}, @code{<limits.h>}, -@code{<stdarg.h>}, and @code{<stddef.h>}; since AMD1, also those in -@code{<iso646.h>}; and in C99, also those in @code{<stdbool.h>} and -@code{<stdint.h>}. In addition, complex types, added in C99, are not -required for freestanding implementations. The standard also defines -two environments for programs, a @dfn{freestanding environment}, -required of all implementations and which may not have library -facilities beyond those required of freestanding implementations, -where the handling of program startup and termination are -implementation-defined, and a @dfn{hosted environment}, which is not -required, in which all the library facilities are provided and startup -is through a function @code{int main (void)} or @code{int main (int, -char *[])}. An OS kernel would be a freestanding environment; a -program using the facilities of an operating system would normally be -in a hosted implementation. - -@opindex ffreestanding -GCC aims towards being usable as a conforming freestanding -implementation, or as the compiler for a conforming hosted -implementation. By default, it will act as the compiler for a hosted -implementation, defining @code{__STDC_HOSTED__} as @code{1} and -presuming that when the names of ISO C functions are used, they have -the semantics defined in the standard. To make it act as a conforming -freestanding implementation for a freestanding environment, use the -option @option{-ffreestanding}; it will then define -@code{__STDC_HOSTED__} to @code{0} and not make assumptions about the -meanings of function names from the standard library. To build an OS -kernel, you may well still need to make your own arrangements for -linking and startup. @xref{C Dialect Options,,Options Controlling C -Dialect}. - -GCC does not provide the library facilities required only of hosted -implementations, nor yet all the facilities required by C99 of -freestanding implementations; to use the facilities of a hosted -environment, you will need to find them elsewhere (for example, in the -GNU C library). @xref{Standard Libraries,,Standard Libraries}. - -For references to Technical Corrigenda, Rationale documents and -information concerning the history of C that is available online, see -@uref{http://gcc.gnu.org/readings.html} - -@c FIXME: details of C++ standard. - -There is no formal written standard for Objective-C@. The most -authoritative manual is ``Object-Oriented Programming and the -Objective-C Language'', available at a number of web sites; -@uref{http://developer.apple.com/techpubs/macosx/Cocoa/ObjectiveC/} has a -recent version, while @uref{http://www.toodarkpark.org/computers/objc/} -is an older example. @uref{http://www.gnustep.org} includes useful -information as well. - -@xref{Top, GNAT Reference Manual, About This Guide, gnat_rm, -GNAT Reference Manual}, for information on standard -conformance and compatibility of the Ada compiler. - -@xref{References,,Language Definition References, chill, GNU Chill}, -for details of the CHILL standard. - -@xref{Language,,The GNU Fortran Language, g77, Using and Porting GNU -Fortran}, for details of the Fortran language supported by GCC@. - -@xref{Compatibility,,Compatibility with the Java Platform, gcj, GNU gcj}, -for details of compatibility between @code{gcj} and the Java Platform. + +@include frontends.texi + +@include standards.texi @include invoke.texi @@ -524,2230 +292,15 @@ for details of compatibility between @code{gcj} and the Java Platform. @include gcov.texi -@node Trouble -@chapter Known Causes of Trouble with GCC -@cindex bugs, known -@cindex installation trouble -@cindex known causes of trouble - -This section describes known problems that affect users of GCC@. Most -of these are not GCC bugs per se---if they were, we would fix them. -But the result for a user may be like the result of a bug. - -Some of these problems are due to bugs in other software, some are -missing features that are too much work to add, and some are places -where people's opinions differ as to what is best. - -@menu -* Actual Bugs:: Bugs we will fix later. -* Cross-Compiler Problems:: Common problems of cross compiling with GCC. -* Interoperation:: Problems using GCC with other compilers, - and with certain linkers, assemblers and debuggers. -* External Bugs:: Problems compiling certain programs. -* Incompatibilities:: GCC is incompatible with traditional C. -* Fixed Headers:: GCC uses corrected versions of system header files. - This is necessary, but doesn't always work smoothly. -* Standard Libraries:: GCC uses the system C library, which might not be - compliant with the ISO C standard. -* Disappointments:: Regrettable things we can't change, but not quite bugs. -* C++ Misunderstandings:: Common misunderstandings with GNU C++. -* Protoize Caveats:: Things to watch out for when using @code{protoize}. -* Non-bugs:: Things we think are right, but some others disagree. -* Warnings and Errors:: Which problems in your code get warnings, - and which get errors. -@end menu - -@node Actual Bugs -@section Actual Bugs We Haven't Fixed Yet - -@itemize @bullet -@item -The @code{fixincludes} script interacts badly with automounters; if the -directory of system header files is automounted, it tends to be -unmounted while @code{fixincludes} is running. This would seem to be a -bug in the automounter. We don't know any good way to work around it. - -@item -The @code{fixproto} script will sometimes add prototypes for the -@code{sigsetjmp} and @code{siglongjmp} functions that reference the -@code{jmp_buf} type before that type is defined. To work around this, -edit the offending file and place the typedef in front of the -prototypes. - -@item -@opindex pedantic-errors -When @option{-pedantic-errors} is specified, GCC will incorrectly give -an error message when a function name is specified in an expression -involving the comma operator. -@end itemize - -@node Cross-Compiler Problems -@section Cross-Compiler Problems - -You may run into problems with cross compilation on certain machines, -for several reasons. - -@itemize @bullet -@item -Cross compilation can run into trouble for certain machines because -some target machines' assemblers require floating point numbers to be -written as @emph{integer} constants in certain contexts. - -The compiler writes these integer constants by examining the floating -point value as an integer and printing that integer, because this is -simple to write and independent of the details of the floating point -representation. But this does not work if the compiler is running on -a different machine with an incompatible floating point format, or -even a different byte-ordering. - -In addition, correct constant folding of floating point values -requires representing them in the target machine's format. -(The C standard does not quite require this, but in practice -it is the only way to win.) - -It is now possible to overcome these problems by defining macros such -as @code{REAL_VALUE_TYPE}. But doing so is a substantial amount of -work for each target machine. -@ifset INTERNALS -@xref{Cross-compilation}. -@end ifset -@ifclear INTERNALS -@xref{Cross-compilation,,Cross Compilation and Floating Point Format, -gcc.info, Using and Porting GCC}. -@end ifclear - -@item -At present, the program @file{mips-tfile} which adds debug -support to object files on MIPS systems does not work in a cross -compile environment. -@end itemize - -@node Interoperation -@section Interoperation - -This section lists various difficulties encountered in using GCC -together with other compilers or with the assemblers, linkers, -libraries and debuggers on certain systems. - -@itemize @bullet -@item -Objective-C does not work on the RS/6000. - -@item -G++ does not do name mangling in the same way as other C++ -compilers. This means that object files compiled with one compiler -cannot be used with another. - -This effect is intentional, to protect you from more subtle problems. -Compilers differ as to many internal details of C++ implementation, -including: how class instances are laid out, how multiple inheritance is -implemented, and how virtual function calls are handled. If the name -encoding were made the same, your programs would link against libraries -provided from other compilers---but the programs would then crash when -run. Incompatible libraries are then detected at link time, rather than -at run time. - -@item -Older GDB versions sometimes fail to read the output of GCC version -2. If you have trouble, get GDB version 4.4 or later. - -@item -@cindex DBX -DBX rejects some files produced by GCC, though it accepts similar -constructs in output from PCC@. Until someone can supply a coherent -description of what is valid DBX input and what is not, there is -nothing I can do about these problems. You are on your own. - -@item -The GNU assembler (GAS) does not support PIC@. To generate PIC code, you -must use some other assembler, such as @file{/bin/as}. - -@item -On some BSD systems, including some versions of Ultrix, use of profiling -causes static variable destructors (currently used only in C++) not to -be run. - -@ignore -@cindex @code{vfork}, for the Sun-4 -@item -There is a bug in @code{vfork} on the Sun-4 which causes the registers -of the child process to clobber those of the parent. Because of this, -programs that call @code{vfork} are likely to lose when compiled -optimized with GCC when the child code alters registers which contain -C variables in the parent. This affects variables which are live in the -parent across the call to @code{vfork}. - -If you encounter this, you can work around the problem by declaring -variables @code{volatile} in the function that calls @code{vfork}, until -the problem goes away, or by not declaring them @code{register} and not -using @option{-O} for those source files. -@end ignore - -@item -On some SGI systems, when you use @option{-lgl_s} as an option, -it gets translated magically to @samp{-lgl_s -lX11_s -lc_s}. -Naturally, this does not happen when you use GCC@. -You must specify all three options explicitly. - -@item -On a Sparc, GCC aligns all values of type @code{double} on an 8-byte -boundary, and it expects every @code{double} to be so aligned. The Sun -compiler usually gives @code{double} values 8-byte alignment, with one -exception: function arguments of type @code{double} may not be aligned. - -As a result, if a function compiled with Sun CC takes the address of an -argument of type @code{double} and passes this pointer of type -@code{double *} to a function compiled with GCC, dereferencing the -pointer may cause a fatal signal. - -One way to solve this problem is to compile your entire program with GCC@. -Another solution is to modify the function that is compiled with -Sun CC to copy the argument into a local variable; local variables -are always properly aligned. A third solution is to modify the function -that uses the pointer to dereference it via the following function -@code{access_double} instead of directly with @samp{*}: - -@smallexample -inline double -access_double (double *unaligned_ptr) -@{ - union d2i @{ double d; int i[2]; @}; - - union d2i *p = (union d2i *) unaligned_ptr; - union d2i u; - - u.i[0] = p->i[0]; - u.i[1] = p->i[1]; - - return u.d; -@} -@end smallexample - -@noindent -Storing into the pointer can be done likewise with the same union. - -@item -On Solaris, the @code{malloc} function in the @file{libmalloc.a} library -may allocate memory that is only 4 byte aligned. Since GCC on the -Sparc assumes that doubles are 8 byte aligned, this may result in a -fatal signal if doubles are stored in memory allocated by the -@file{libmalloc.a} library. - -The solution is to not use the @file{libmalloc.a} library. Use instead -@code{malloc} and related functions from @file{libc.a}; they do not have -this problem. - -@item -Sun forgot to include a static version of @file{libdl.a} with some -versions of SunOS (mainly 4.1). This results in undefined symbols when -linking static binaries (that is, if you use @option{-static}). If you -see undefined symbols @code{_dlclose}, @code{_dlsym} or @code{_dlopen} -when linking, compile and link against the file -@file{mit/util/misc/dlsym.c} from the MIT version of X windows. - -@item -The 128-bit long double format that the Sparc port supports currently -works by using the architecturally defined quad-word floating point -instructions. Since there is no hardware that supports these -instructions they must be emulated by the operating system. Long -doubles do not work in Sun OS versions 4.0.3 and earlier, because the -kernel emulator uses an obsolete and incompatible format. Long doubles -do not work in Sun OS version 4.1.1 due to a problem in a Sun library. -Long doubles do work on Sun OS versions 4.1.2 and higher, but GCC -does not enable them by default. Long doubles appear to work in Sun OS -5.x (Solaris 2.x). - -@item -On HP-UX version 9.01 on the HP PA, the HP compiler @code{cc} does not -compile GCC correctly. We do not yet know why. However, GCC -compiled on earlier HP-UX versions works properly on HP-UX 9.01 and can -compile itself properly on 9.01. - -@item -On the HP PA machine, ADB sometimes fails to work on functions compiled -with GCC@. Specifically, it fails to work on functions that use -@code{alloca} or variable-size arrays. This is because GCC doesn't -generate HP-UX unwind descriptors for such functions. It may even be -impossible to generate them. - -@item -Debugging (@option{-g}) is not supported on the HP PA machine, unless you use -the preliminary GNU tools (@pxref{Installation}). - -@item -Taking the address of a label may generate errors from the HP-UX -PA assembler. GAS for the PA does not have this problem. - -@item -Using floating point parameters for indirect calls to static functions -will not work when using the HP assembler. There simply is no way for GCC -to specify what registers hold arguments for static functions when using -the HP assembler. GAS for the PA does not have this problem. - -@item -In extremely rare cases involving some very large functions you may -receive errors from the HP linker complaining about an out of bounds -unconditional branch offset. This used to occur more often in previous -versions of GCC, but is now exceptionally rare. If you should run -into it, you can work around by making your function smaller. - -@item -GCC compiled code sometimes emits warnings from the HP-UX assembler of -the form: - -@smallexample -(warning) Use of GR3 when - frame >= 8192 may cause conflict. -@end smallexample - -These warnings are harmless and can be safely ignored. - -@item -The current version of the assembler (@file{/bin/as}) for the RS/6000 -has certain problems that prevent the @option{-g} option in GCC from -working. Note that @file{Makefile.in} uses @option{-g} by default when -compiling @file{libgcc2.c}. - -IBM has produced a fixed version of the assembler. The upgraded -assembler unfortunately was not included in any of the AIX 3.2 update -PTF releases (3.2.2, 3.2.3, or 3.2.3e). Users of AIX 3.1 should request -PTF U403044 from IBM and users of AIX 3.2 should request PTF U416277. -See the file @file{README.RS6000} for more details on these updates. - -You can test for the presence of a fixed assembler by using the -command - -@smallexample -as -u < /dev/null -@end smallexample - -@noindent -If the command exits normally, the assembler fix already is installed. -If the assembler complains that @option{-u} is an unknown flag, you need to -order the fix. - -@item -On the IBM RS/6000, compiling code of the form - -@smallexample -extern int foo; - -@dots{} foo @dots{} - -static int foo; -@end smallexample - -@noindent -will cause the linker to report an undefined symbol @code{foo}. -Although this behavior differs from most other systems, it is not a -bug because redefining an @code{extern} variable as @code{static} -is undefined in ISO C@. - -@item -AIX on the RS/6000 provides support (NLS) for environments outside of -the United States. Compilers and assemblers use NLS to support -locale-specific representations of various objects including -floating-point numbers (@samp{.} vs @samp{,} for separating decimal fractions). -There have been problems reported where the library linked with GCC does -not produce the same floating-point formats that the assembler accepts. -If you have this problem, set the @env{LANG} environment variable to -@samp{C} or @samp{En_US}. - -@item -@opindex fdollars-in-identifiers -Even if you specify @option{-fdollars-in-identifiers}, -you cannot successfully use @samp{$} in identifiers on the RS/6000 due -to a restriction in the IBM assembler. GAS supports these -identifiers. - -@item -On the RS/6000, XLC version 1.3.0.0 will miscompile @file{jump.c}. XLC -version 1.3.0.1 or later fixes this problem. You can obtain XLC-1.3.0.2 -by requesting PTF 421749 from IBM@. - -@item -@opindex mno-serialize-volatile -There is an assembler bug in versions of DG/UX prior to 5.4.2.01 that -occurs when the @samp{fldcr} instruction is used. GCC uses -@samp{fldcr} on the 88100 to serialize volatile memory references. Use -the option @option{-mno-serialize-volatile} if your version of the -assembler has this bug. - -@item -On VMS, GAS versions 1.38.1 and earlier may cause spurious warning -messages from the linker. These warning messages complain of mismatched -psect attributes. You can ignore them. @xref{VMS Install}. - -@item -On NewsOS version 3, if you include both of the files @file{stddef.h} -and @file{sys/types.h}, you get an error because there are two typedefs -of @code{size_t}. You should change @file{sys/types.h} by adding these -lines around the definition of @code{size_t}: - -@smallexample -#ifndef _SIZE_T -#define _SIZE_T -@var{actual-typedef-here} -#endif -@end smallexample - -@cindex Alliant -@item -On the Alliant, the system's own convention for returning structures -and unions is unusual, and is not compatible with GCC no matter -what options are used. - -@cindex RT PC -@cindex IBM RT PC -@item -@opindex mhc-struct-return -On the IBM RT PC, the MetaWare HighC compiler (hc) uses a different -convention for structure and union returning. Use the option -@option{-mhc-struct-return} to tell GCC to use a convention compatible -with it. - -@cindex VAX calling convention -@cindex Ultrix calling convention -@item -@opindex fcall-saved -On Ultrix, the Fortran compiler expects registers 2 through 5 to be saved -by function calls. However, the C compiler uses conventions compatible -with BSD Unix: registers 2 through 5 may be clobbered by function calls. - -GCC uses the same convention as the Ultrix C compiler. You can use -these options to produce code compatible with the Fortran compiler: - -@smallexample --fcall-saved-r2 -fcall-saved-r3 -fcall-saved-r4 -fcall-saved-r5 -@end smallexample - -@item -On the WE32k, you may find that programs compiled with GCC do not -work with the standard shared C library. You may need to link with -the ordinary C compiler. If you do so, you must specify the following -options: - -@smallexample --L/usr/local/lib/gcc-lib/we32k-att-sysv/2.8.1 -lgcc -lc_s -@end smallexample - -The first specifies where to find the library @file{libgcc.a} -specified with the @option{-lgcc} option. - -GCC does linking by invoking @command{ld}, just as @command{cc} does, and -there is no reason why it @emph{should} matter which compilation program -you use to invoke @command{ld}. If someone tracks this problem down, -it can probably be fixed easily. - -@item -On the Alpha, you may get assembler errors about invalid syntax as a -result of floating point constants. This is due to a bug in the C -library functions @code{ecvt}, @code{fcvt} and @code{gcvt}. Given valid -floating point numbers, they sometimes print @samp{NaN}. - -@item -On Irix 4.0.5F (and perhaps in some other versions), an assembler bug -sometimes reorders instructions incorrectly when optimization is turned -on. If you think this may be happening to you, try using the GNU -assembler; GAS version 2.1 supports ECOFF on Irix. - -@opindex noasmopt -Or use the @option{-noasmopt} option when you compile GCC with itself, -and then again when you compile your program. (This is a temporary -kludge to turn off assembler optimization on Irix.) If this proves to -be what you need, edit the assembler spec in the file @file{specs} so -that it unconditionally passes @option{-O0} to the assembler, and never -passes @option{-O2} or @option{-O3}. -@end itemize - -@node External Bugs -@section Problems Compiling Certain Programs - -@c prevent bad page break with this line -Certain programs have problems compiling. - -@itemize @bullet -@item -Parse errors may occur compiling X11 on a Decstation running Ultrix 4.2 -because of problems in DEC's versions of the X11 header files -@file{X11/Xlib.h} and @file{X11/Xutil.h}. People recommend adding -@option{-I/usr/include/mit} to use the MIT versions of the header files, -using the @option{-traditional} switch to turn off ISO C, or fixing the -header files by adding this: - -@example -#ifdef __STDC__ -#define NeedFunctionPrototypes 0 -#endif -@end example - -@item -On various 386 Unix systems derived from System V, including SCO, ISC, -and ESIX, you may get error messages about running out of virtual memory -while compiling certain programs. - -You can prevent this problem by linking GCC with the GNU malloc -(which thus replaces the malloc that comes with the system). GNU malloc -is available as a separate package, and also in the file -@file{src/gmalloc.c} in the GNU Emacs 19 distribution. - -If you have installed GNU malloc as a separate library package, use this -option when you relink GCC: - -@example -MALLOC=/usr/local/lib/libgmalloc.a -@end example - -Alternatively, if you have compiled @file{gmalloc.c} from Emacs 19, copy -the object file to @file{gmalloc.o} and use this option when you relink -GCC: - -@example -MALLOC=gmalloc.o -@end example -@end itemize - -@node Incompatibilities -@section Incompatibilities of GCC -@cindex incompatibilities of GCC -@opindex traditional - -There are several noteworthy incompatibilities between GNU C and K&R -(non-ISO) versions of C@. The @option{-traditional} option -eliminates many of these incompatibilities, @emph{but not all}, by -telling GCC to behave like a K&R C compiler. - -@itemize @bullet -@cindex string constants -@cindex read-only strings -@cindex shared strings -@item -GCC normally makes string constants read-only. If several -identical-looking string constants are used, GCC stores only one -copy of the string. - -@cindex @code{mktemp}, and constant strings -One consequence is that you cannot call @code{mktemp} with a string -constant argument. The function @code{mktemp} always alters the -string its argument points to. - -@cindex @code{sscanf}, and constant strings -@cindex @code{fscanf}, and constant strings -@cindex @code{scanf}, and constant strings -Another consequence is that @code{sscanf} does not work on some systems -when passed a string constant as its format control string or input. -This is because @code{sscanf} incorrectly tries to write into the string -constant. Likewise @code{fscanf} and @code{scanf}. - -@opindex fwritable-strings -The best solution to these problems is to change the program to use -@code{char}-array variables with initialization strings for these -purposes instead of string constants. But if this is not possible, -you can use the @option{-fwritable-strings} flag, which directs GCC -to handle string constants the same way most C compilers do. -@option{-traditional} also has this effect, among others. - -@item -@code{-2147483648} is positive. - -This is because 2147483648 cannot fit in the type @code{int}, so -(following the ISO C rules) its data type is @code{unsigned long int}. -Negating this value yields 2147483648 again. - -@item -GCC does not substitute macro arguments when they appear inside of -string constants. For example, the following macro in GCC - -@example -#define foo(a) "a" -@end example - -@noindent -will produce output @code{"a"} regardless of what the argument @var{a} is. - -The @option{-traditional} option directs GCC to handle such cases -(among others) in the old-fashioned (non-ISO) fashion. - -@cindex @code{setjmp} incompatibilities -@cindex @code{longjmp} incompatibilities -@item -When you use @code{setjmp} and @code{longjmp}, the only automatic -variables guaranteed to remain valid are those declared -@code{volatile}. This is a consequence of automatic register -allocation. Consider this function: - -@example -jmp_buf j; - -foo () -@{ - int a, b; - - a = fun1 (); - if (setjmp (j)) - return a; - - a = fun2 (); - /* @r{@code{longjmp (j)} may occur in @code{fun3}.} */ - return a + fun3 (); -@} -@end example - -Here @code{a} may or may not be restored to its first value when the -@code{longjmp} occurs. If @code{a} is allocated in a register, then -its first value is restored; otherwise, it keeps the last value stored -in it. - -@opindex W -If you use the @option{-W} option with the @option{-O} option, you will -get a warning when GCC thinks such a problem might be possible. - -The @option{-traditional} option directs GCC to put variables in -the stack by default, rather than in registers, in functions that -call @code{setjmp}. This results in the behavior found in -traditional C compilers. - -@item -Programs that use preprocessing directives in the middle of macro -arguments do not work with GCC@. For example, a program like this -will not work: - -@example -@group -foobar ( -#define luser - hack) -@end group -@end example - -ISO C does not permit such a construct. It would make sense to support -it when @option{-traditional} is used, but it is too much work to -implement. - -@item -K&R compilers allow comments to cross over an inclusion boundary -(i.e.@: started in an include file and ended in the including file). I think -this would be quite ugly and can't imagine it could be needed. - -@cindex external declaration scope -@cindex scope of external declarations -@cindex declaration scope -@item -Declarations of external variables and functions within a block apply -only to the block containing the declaration. In other words, they -have the same scope as any other declaration in the same place. - -In some other C compilers, a @code{extern} declaration affects all the -rest of the file even if it happens within a block. - -The @option{-traditional} option directs GCC to treat all @code{extern} -declarations as global, like traditional compilers. - -@item -In traditional C, you can combine @code{long}, etc., with a typedef name, -as shown here: - -@example -typedef int foo; -typedef long foo bar; -@end example - -In ISO C, this is not allowed: @code{long} and other type modifiers -require an explicit @code{int}. Because this criterion is expressed -by Bison grammar rules rather than C code, the @option{-traditional} -flag cannot alter it. - -@cindex typedef names as function parameters -@item -PCC allows typedef names to be used as function parameters. The -difficulty described immediately above applies here too. - -@item -When in @option{-traditional} mode, GCC allows the following erroneous -pair of declarations to appear together in a given scope: - -@example -typedef int foo; -typedef foo foo; -@end example - -@item -GCC treats all characters of identifiers as significant, even when in -@option{-traditional} mode. According to K&R-1 (2.2), ``No more than the -first eight characters are significant, although more may be used.''. -Also according to K&R-1 (2.2), ``An identifier is a sequence of letters -and digits; the first character must be a letter. The underscore _ -counts as a letter.'', but GCC also allows dollar signs in identifiers. - -@cindex whitespace -@item -PCC allows whitespace in the middle of compound assignment operators -such as @samp{+=}. GCC, following the ISO standard, does not -allow this. The difficulty described immediately above applies here -too. - -@cindex apostrophes -@cindex ' -@item -GCC complains about unterminated character constants inside of -preprocessing conditionals that fail. Some programs have English -comments enclosed in conditionals that are guaranteed to fail; if these -comments contain apostrophes, GCC will probably report an error. For -example, this code would produce an error: - -@example -#if 0 -You can't expect this to work. -#endif -@end example - -The best solution to such a problem is to put the text into an actual -C comment delimited by @samp{/*@dots{}*/}. However, -@option{-traditional} suppresses these error messages. - -@item -Many user programs contain the declaration @samp{long time ();}. In the -past, the system header files on many systems did not actually declare -@code{time}, so it did not matter what type your program declared it to -return. But in systems with ISO C headers, @code{time} is declared to -return @code{time_t}, and if that is not the same as @code{long}, then -@samp{long time ();} is erroneous. - -The solution is to change your program to use appropriate system headers -(@code{<time.h>} on systems with ISO C headers) and not to declare -@code{time} if the system header files declare it, or failing that to -use @code{time_t} as the return type of @code{time}. - -@cindex @code{float} as function value type -@item -When compiling functions that return @code{float}, PCC converts it to -a double. GCC actually returns a @code{float}. If you are concerned -with PCC compatibility, you should declare your functions to return -@code{double}; you might as well say what you mean. - -@cindex structures -@cindex unions -@item -When compiling functions that return structures or unions, GCC -output code normally uses a method different from that used on most -versions of Unix. As a result, code compiled with GCC cannot call -a structure-returning function compiled with PCC, and vice versa. - -The method used by GCC is as follows: a structure or union which is -1, 2, 4 or 8 bytes long is returned like a scalar. A structure or union -with any other size is stored into an address supplied by the caller -(usually in a special, fixed register, but on some machines it is passed -on the stack). The machine-description macros @code{STRUCT_VALUE} and -@code{STRUCT_INCOMING_VALUE} tell GCC where to pass this address. - -By contrast, PCC on most target machines returns structures and unions -of any size by copying the data into an area of static storage, and then -returning the address of that storage as if it were a pointer value. -The caller must copy the data from that memory area to the place where -the value is wanted. GCC does not use this method because it is -slower and nonreentrant. - -On some newer machines, PCC uses a reentrant convention for all -structure and union returning. GCC on most of these machines uses a -compatible convention when returning structures and unions in memory, -but still returns small structures and unions in registers. - -@opindex fpcc-struct-return -You can tell GCC to use a compatible convention for all structure and -union returning with the option @option{-fpcc-struct-return}. - -@cindex preprocessing tokens -@cindex preprocessing numbers -@item -GCC complains about program fragments such as @samp{0x74ae-0x4000} -which appear to be two hexadecimal constants separated by the minus -operator. Actually, this string is a single @dfn{preprocessing token}. -Each such token must correspond to one token in C@. Since this does not, -GCC prints an error message. Although it may appear obvious that what -is meant is an operator and two values, the ISO C standard specifically -requires that this be treated as erroneous. - -A @dfn{preprocessing token} is a @dfn{preprocessing number} if it -begins with a digit and is followed by letters, underscores, digits, -periods and @samp{e+}, @samp{e-}, @samp{E+}, @samp{E-}, @samp{p+}, -@samp{p-}, @samp{P+}, or @samp{P-} character sequences. (In strict C89 -mode, the sequences @samp{p+}, @samp{p-}, @samp{P+} and @samp{P-} cannot -appear in preprocessing numbers.) - -To make the above program fragment valid, place whitespace in front of -the minus sign. This whitespace will end the preprocessing number. -@end itemize - -@node Fixed Headers -@section Fixed Header Files - -GCC needs to install corrected versions of some system header files. -This is because most target systems have some header files that won't -work with GCC unless they are changed. Some have bugs, some are -incompatible with ISO C, and some depend on special features of other -compilers. - -Installing GCC automatically creates and installs the fixed header -files, by running a program called @code{fixincludes} (or for certain -targets an alternative such as @code{fixinc.svr4}). Normally, you -don't need to pay attention to this. But there are cases where it -doesn't do the right thing automatically. - -@itemize @bullet -@item -If you update the system's header files, such as by installing a new -system version, the fixed header files of GCC are not automatically -updated. The easiest way to update them is to reinstall GCC@. (If -you want to be clever, look in the makefile and you can find a -shortcut.) - -@item -On some systems, in particular SunOS 4, header file directories contain -machine-specific symbolic links in certain places. This makes it -possible to share most of the header files among hosts running the -same version of SunOS 4 on different machine models. - -The programs that fix the header files do not understand this special -way of using symbolic links; therefore, the directory of fixed header -files is good only for the machine model used to build it. - -In SunOS 4, only programs that look inside the kernel will notice the -difference between machine models. Therefore, for most purposes, you -need not be concerned about this. - -It is possible to make separate sets of fixed header files for the -different machine models, and arrange a structure of symbolic links so -as to use the proper set, but you'll have to do this by hand. - -@item -On Lynxos, GCC by default does not fix the header files. This is -because bugs in the shell cause the @code{fixincludes} script to fail. - -This means you will encounter problems due to bugs in the system header -files. It may be no comfort that they aren't GCC's fault, but it -does mean that there's nothing for us to do about them. -@end itemize - -@node Standard Libraries -@section Standard Libraries - -@opindex Wall -GCC by itself attempts to be a conforming freestanding implementation. -@xref{Standards,,Language Standards Supported by GCC}, for details of -what this means. Beyond the library facilities required of such an -implementation, the rest of the C library is supplied by the vendor of -the operating system. If that C library doesn't conform to the C -standards, then your programs might get warnings (especially when using -@option{-Wall}) that you don't expect. - -For example, the @code{sprintf} function on SunOS 4.1.3 returns -@code{char *} while the C standard says that @code{sprintf} returns an -@code{int}. The @code{fixincludes} program could make the prototype for -this function match the Standard, but that would be wrong, since the -function will still return @code{char *}. - -If you need a Standard compliant library, then you need to find one, as -GCC does not provide one. The GNU C library (called @code{glibc}) -provides ISO C, POSIX, BSD, SystemV and X/Open compatibility for -GNU/Linux and HURD-based GNU systems; no recent version of it supports -other systems, though some very old versions did. Version 2.2 of the -GNU C library includes nearly complete C99 support. You could also ask -your operating system vendor if newer libraries are available. - -@node Disappointments -@section Disappointments and Misunderstandings - -These problems are perhaps regrettable, but we don't know any practical -way around them. - -@itemize @bullet -@item -Certain local variables aren't recognized by debuggers when you compile -with optimization. - -This occurs because sometimes GCC optimizes the variable out of -existence. There is no way to tell the debugger how to compute the -value such a variable ``would have had'', and it is not clear that would -be desirable anyway. So GCC simply does not mention the eliminated -variable when it writes debugging information. - -You have to expect a certain amount of disagreement between the -executable and your source code, when you use optimization. - -@cindex conflicting types -@cindex scope of declaration -@item -Users often think it is a bug when GCC reports an error for code -like this: - -@example -int foo (struct mumble *); - -struct mumble @{ @dots{} @}; - -int foo (struct mumble *x) -@{ @dots{} @} -@end example - -This code really is erroneous, because the scope of @code{struct -mumble} in the prototype is limited to the argument list containing it. -It does not refer to the @code{struct mumble} defined with file scope -immediately below---they are two unrelated types with similar names in -different scopes. - -But in the definition of @code{foo}, the file-scope type is used -because that is available to be inherited. Thus, the definition and -the prototype do not match, and you get an error. - -This behavior may seem silly, but it's what the ISO standard specifies. -It is easy enough for you to make your code work by moving the -definition of @code{struct mumble} above the prototype. It's not worth -being incompatible with ISO C just to avoid an error for the example -shown above. - -@item -Accesses to bit-fields even in volatile objects works by accessing larger -objects, such as a byte or a word. You cannot rely on what size of -object is accessed in order to read or write the bit-field; it may even -vary for a given bit-field according to the precise usage. - -If you care about controlling the amount of memory that is accessed, use -volatile but do not use bit-fields. - -@item -GCC comes with shell scripts to fix certain known problems in system -header files. They install corrected copies of various header files in -a special directory where only GCC will normally look for them. The -scripts adapt to various systems by searching all the system header -files for the problem cases that we know about. - -If new system header files are installed, nothing automatically arranges -to update the corrected header files. You will have to reinstall GCC -to fix the new header files. More specifically, go to the build -directory and delete the files @file{stmp-fixinc} and -@file{stmp-headers}, and the subdirectory @code{include}; then do -@samp{make install} again. - -@item -@cindex floating point precision -On 68000 and x86 systems, for instance, you can get paradoxical results -if you test the precise values of floating point numbers. For example, -you can find that a floating point value which is not a NaN is not equal -to itself. This results from the fact that the floating point registers -hold a few more bits of precision than fit in a @code{double} in memory. -Compiled code moves values between memory and floating point registers -at its convenience, and moving them into memory truncates them. - -@opindex ffloat-store -You can partially avoid this problem by using the @option{-ffloat-store} -option (@pxref{Optimize Options}). - -@item -On the MIPS, variable argument functions using @file{varargs.h} -cannot have a floating point value for the first argument. The -reason for this is that in the absence of a prototype in scope, -if the first argument is a floating point, it is passed in a -floating point register, rather than an integer register. - -If the code is rewritten to use the ISO standard @file{stdarg.h} -method of variable arguments, and the prototype is in scope at -the time of the call, everything will work fine. - -@item -On the H8/300 and H8/300H, variable argument functions must be -implemented using the ISO standard @file{stdarg.h} method of -variable arguments. Furthermore, calls to functions using @file{stdarg.h} -variable arguments must have a prototype for the called function -in scope at the time of the call. -@end itemize - -@node C++ Misunderstandings -@section Common Misunderstandings with GNU C++ - -@cindex misunderstandings in C++ -@cindex surprises in C++ -@cindex C++ misunderstandings -C++ is a complex language and an evolving one, and its standard -definition (the ISO C++ standard) was only recently completed. As a -result, your C++ compiler may occasionally surprise you, even when its -behavior is correct. This section discusses some areas that frequently -give rise to questions of this sort. - -@menu -* Static Definitions:: Static member declarations are not definitions -* Temporaries:: Temporaries may vanish before you expect -* Copy Assignment:: Copy Assignment operators copy virtual bases twice -@end menu - -@node Static Definitions -@subsection Declare @emph{and} Define Static Members - -@cindex C++ static data, declaring and defining -@cindex static data in C++, declaring and defining -@cindex declaring static data in C++ -@cindex defining static data in C++ -When a class has static data members, it is not enough to @emph{declare} -the static member; you must also @emph{define} it. For example: - -@example -class Foo -@{ - @dots{} - void method(); - static int bar; -@}; -@end example - -This declaration only establishes that the class @code{Foo} has an -@code{int} named @code{Foo::bar}, and a member function named -@code{Foo::method}. But you still need to define @emph{both} -@code{method} and @code{bar} elsewhere. According to the ISO -standard, you must supply an initializer in one (and only one) source -file, such as: - -@example -int Foo::bar = 0; -@end example - -Other C++ compilers may not correctly implement the standard behavior. -As a result, when you switch to @code{g++} from one of these compilers, -you may discover that a program that appeared to work correctly in fact -does not conform to the standard: @code{g++} reports as undefined -symbols any static data members that lack definitions. - -@node Temporaries -@subsection Temporaries May Vanish Before You Expect - -@cindex temporaries, lifetime of -@cindex portions of temporary objects, pointers to -It is dangerous to use pointers or references to @emph{portions} of a -temporary object. The compiler may very well delete the object before -you expect it to, leaving a pointer to garbage. The most common place -where this problem crops up is in classes like string classes, -especially ones that define a conversion function to type @code{char *} -or @code{const char *}---which is one reason why the standard -@code{string} class requires you to call the @code{c_str} member -function. However, any class that returns a pointer to some internal -structure is potentially subject to this problem. - -For example, a program may use a function @code{strfunc} that returns -@code{string} objects, and another function @code{charfunc} that -operates on pointers to @code{char}: - -@example -string strfunc (); -void charfunc (const char *); - -void -f () -@{ - const char *p = strfunc().c_str(); - @dots{} - charfunc (p); - @dots{} - charfunc (p); -@} -@end example - -@noindent -In this situation, it may seem reasonable to save a pointer to the C -string returned by the @code{c_str} member function and use that rather -than call @code{c_str} repeatedly. However, the temporary string -created by the call to @code{strfunc} is destroyed after @code{p} is -initialized, at which point @code{p} is left pointing to freed memory. - -Code like this may run successfully under some other compilers, -particularly obsolete cfront-based compilers that delete temporaries -along with normal local variables. However, the GNU C++ behavior is -standard-conforming, so if your program depends on late destruction of -temporaries it is not portable. - -The safe way to write such code is to give the temporary a name, which -forces it to remain until the end of the scope of the name. For -example: - -@example -string& tmp = strfunc (); -charfunc (tmp.c_str ()); -@end example - -@node Copy Assignment -@subsection Implicit Copy-Assignment for Virtual Bases - -When a base class is virtual, only one subobject of the base class -belongs to each full object. Also, the constructors and destructors are -invoked only once, and called from the most-derived class. However, such -objects behave unspecified when being assigned. For example: - -@example -struct Base@{ - char *name; - Base(char *n) : name(strdup(n))@{@} - Base& operator= (const Base& other)@{ - free (name); - name = strdup (other.name); - @} -@}; - -struct A:virtual Base@{ - int val; - A():Base("A")@{@} -@}; - -struct B:virtual Base@{ - int bval; - B():Base("B")@{@} -@}; - -struct Derived:public A, public B@{ - Derived():Base("Derived")@{@} -@}; - -void func(Derived &d1, Derived &d2) -@{ - d1 = d2; -@} -@end example - -The C++ standard specifies that @samp{Base::Base} is only called once -when constructing or copy-constructing a Derived object. It is -unspecified whether @samp{Base::operator=} is called more than once when -the implicit copy-assignment for Derived objects is invoked (as it is -inside @samp{func} in the example). - -g++ implements the ``intuitive'' algorithm for copy-assignment: assign all -direct bases, then assign all members. In that algorithm, the virtual -base subobject can be encountered many times. In the example, copying -proceeds in the following order: @samp{val}, @samp{name} (via -@code{strdup}), @samp{bval}, and @samp{name} again. - -If application code relies on copy-assignment, a user-defined -copy-assignment operator removes any uncertainties. With such an -operator, the application can define whether and how the virtual base -subobject is assigned. - -@node Protoize Caveats -@section Caveats of using @command{protoize} - -The conversion programs @command{protoize} and @command{unprotoize} can -sometimes change a source file in a way that won't work unless you -rearrange it. - -@itemize @bullet -@item -@command{protoize} can insert references to a type name or type tag before -the definition, or in a file where they are not defined. - -If this happens, compiler error messages should show you where the new -references are, so fixing the file by hand is straightforward. - -@item -There are some C constructs which @command{protoize} cannot figure out. -For example, it can't determine argument types for declaring a -pointer-to-function variable; this you must do by hand. @command{protoize} -inserts a comment containing @samp{???} each time it finds such a -variable; so you can find all such variables by searching for this -string. ISO C does not require declaring the argument types of -pointer-to-function types. - -@item -Using @command{unprotoize} can easily introduce bugs. If the program -relied on prototypes to bring about conversion of arguments, these -conversions will not take place in the program without prototypes. -One case in which you can be sure @command{unprotoize} is safe is when -you are removing prototypes that were made with @command{protoize}; if -the program worked before without any prototypes, it will work again -without them. - -@opindex Wconversion -You can find all the places where this problem might occur by compiling -the program with the @option{-Wconversion} option. It prints a warning -whenever an argument is converted. - -@item -Both conversion programs can be confused if there are macro calls in and -around the text to be converted. In other words, the standard syntax -for a declaration or definition must not result from expanding a macro. -This problem is inherent in the design of C and cannot be fixed. If -only a few functions have confusing macro calls, you can easily convert -them manually. - -@item -@command{protoize} cannot get the argument types for a function whose -definition was not actually compiled due to preprocessing conditionals. -When this happens, @command{protoize} changes nothing in regard to such -a function. @command{protoize} tries to detect such instances and warn -about them. - -You can generally work around this problem by using @command{protoize} step -by step, each time specifying a different set of @option{-D} options for -compilation, until all of the functions have been converted. There is -no automatic way to verify that you have got them all, however. - -@item -Confusion may result if there is an occasion to convert a function -declaration or definition in a region of source code where there is more -than one formal parameter list present. Thus, attempts to convert code -containing multiple (conditionally compiled) versions of a single -function header (in the same vicinity) may not produce the desired (or -expected) results. - -If you plan on converting source files which contain such code, it is -recommended that you first make sure that each conditionally compiled -region of source code which contains an alternative function header also -contains at least one additional follower token (past the final right -parenthesis of the function header). This should circumvent the -problem. - -@item -@command{unprotoize} can become confused when trying to convert a function -definition or declaration which contains a declaration for a -pointer-to-function formal argument which has the same name as the -function being defined or declared. We recommend you avoid such choices -of formal parameter names. - -@item -You might also want to correct some of the indentation by hand and break -long lines. (The conversion programs don't write lines longer than -eighty characters in any case.) -@end itemize - -@node Non-bugs -@section Certain Changes We Don't Want to Make - -This section lists changes that people frequently request, but which -we do not make because we think GCC is better without them. - -@itemize @bullet -@item -Checking the number and type of arguments to a function which has an -old-fashioned definition and no prototype. - -Such a feature would work only occasionally---only for calls that appear -in the same file as the called function, following the definition. The -only way to check all calls reliably is to add a prototype for the -function. But adding a prototype eliminates the motivation for this -feature. So the feature is not worthwhile. - -@item -Warning about using an expression whose type is signed as a shift count. - -Shift count operands are probably signed more often than unsigned. -Warning about this would cause far more annoyance than good. - -@item -Warning about assigning a signed value to an unsigned variable. - -Such assignments must be very common; warning about them would cause -more annoyance than good. - -@item -Warning when a non-void function value is ignored. - -Coming as I do from a Lisp background, I balk at the idea that there is -something dangerous about discarding a value. There are functions that -return values which some callers may find useful; it makes no sense to -clutter the program with a cast to @code{void} whenever the value isn't -useful. - -@item -@opindex fshort-enums -Making @option{-fshort-enums} the default. - -This would cause storage layout to be incompatible with most other C -compilers. And it doesn't seem very important, given that you can get -the same result in other ways. The case where it matters most is when -the enumeration-valued object is inside a structure, and in that case -you can specify a field width explicitly. - -@item -Making bit-fields unsigned by default on particular machines where ``the -ABI standard'' says to do so. - -The ISO C standard leaves it up to the implementation whether a bit-field -declared plain @code{int} is signed or not. This in effect creates two -alternative dialects of C@. - -@opindex fsigned-bitfields -@opindex funsigned-bitfields -The GNU C compiler supports both dialects; you can specify the signed -dialect with @option{-fsigned-bitfields} and the unsigned dialect with -@option{-funsigned-bitfields}. However, this leaves open the question of -which dialect to use by default. - -Currently, the preferred dialect makes plain bit-fields signed, because -this is simplest. Since @code{int} is the same as @code{signed int} in -every other context, it is cleanest for them to be the same in bit-fields -as well. - -Some computer manufacturers have published Application Binary Interface -standards which specify that plain bit-fields should be unsigned. It is -a mistake, however, to say anything about this issue in an ABI@. This is -because the handling of plain bit-fields distinguishes two dialects of C@. -Both dialects are meaningful on every type of machine. Whether a -particular object file was compiled using signed bit-fields or unsigned -is of no concern to other object files, even if they access the same -bit-fields in the same data structures. - -A given program is written in one or the other of these two dialects. -The program stands a chance to work on most any machine if it is -compiled with the proper dialect. It is unlikely to work at all if -compiled with the wrong dialect. - -Many users appreciate the GNU C compiler because it provides an -environment that is uniform across machines. These users would be -inconvenienced if the compiler treated plain bit-fields differently on -certain machines. - -Occasionally users write programs intended only for a particular machine -type. On these occasions, the users would benefit if the GNU C compiler -were to support by default the same dialect as the other compilers on -that machine. But such applications are rare. And users writing a -program to run on more than one type of machine cannot possibly benefit -from this kind of compatibility. - -This is why GCC does and will treat plain bit-fields in the same -fashion on all types of machines (by default). - -There are some arguments for making bit-fields unsigned by default on all -machines. If, for example, this becomes a universal de facto standard, -it would make sense for GCC to go along with it. This is something -to be considered in the future. - -(Of course, users strongly concerned about portability should indicate -explicitly in each bit-field whether it is signed or not. In this way, -they write programs which have the same meaning in both C dialects.) - -@item -@opindex ansi -@opindex traditional -@opindex std -Undefining @code{__STDC__} when @option{-ansi} is not used. - -Currently, GCC defines @code{__STDC__} as long as you don't use -@option{-traditional}. This provides good results in practice. - -Programmers normally use conditionals on @code{__STDC__} to ask whether -it is safe to use certain features of ISO C, such as function -prototypes or ISO token concatenation. Since plain @command{gcc} supports -all the features of ISO C, the correct answer to these questions is -``yes''. - -Some users try to use @code{__STDC__} to check for the availability of -certain library facilities. This is actually incorrect usage in an ISO -C program, because the ISO C standard says that a conforming -freestanding implementation should define @code{__STDC__} even though it -does not have the library facilities. @samp{gcc -ansi -pedantic} is a -conforming freestanding implementation, and it is therefore required to -define @code{__STDC__}, even though it does not come with an ISO C -library. - -Sometimes people say that defining @code{__STDC__} in a compiler that -does not completely conform to the ISO C standard somehow violates the -standard. This is illogical. The standard is a standard for compilers -that claim to support ISO C, such as @samp{gcc -ansi}---not for other -compilers such as plain @command{gcc}. Whatever the ISO C standard says -is relevant to the design of plain @command{gcc} without @option{-ansi} only -for pragmatic reasons, not as a requirement. - -GCC normally defines @code{__STDC__} to be 1, and in addition -defines @code{__STRICT_ANSI__} if you specify the @option{-ansi} option, -or a @option{-std} option for strict conformance to some version of ISO C@. -On some hosts, system include files use a different convention, where -@code{__STDC__} is normally 0, but is 1 if the user specifies strict -conformance to the C Standard. GCC follows the host convention when -processing system include files, but when processing user files it follows -the usual GNU C convention. - -@item -Undefining @code{__STDC__} in C++. - -Programs written to compile with C++-to-C translators get the -value of @code{__STDC__} that goes with the C compiler that is -subsequently used. These programs must test @code{__STDC__} -to determine what kind of C preprocessor that compiler uses: -whether they should concatenate tokens in the ISO C fashion -or in the traditional fashion. - -These programs work properly with GNU C++ if @code{__STDC__} is defined. -They would not work otherwise. +@include trouble.texi -In addition, many header files are written to provide prototypes in ISO -C but not in traditional C@. Many of these header files can work without -change in C++ provided @code{__STDC__} is defined. If @code{__STDC__} -is not defined, they will all fail, and will all need to be changed to -test explicitly for C++ as well. - -@item -Deleting ``empty'' loops. - -Historically, GCC has not deleted ``empty'' loops under the -assumption that the most likely reason you would put one in a program is -to have a delay, so deleting them will not make real programs run any -faster. - -However, the rationale here is that optimization of a nonempty loop -cannot produce an empty one, which holds for C but is not always the -case for C++. - -@opindex funroll-loops -Moreover, with @option{-funroll-loops} small ``empty'' loops are already -removed, so the current behavior is both sub-optimal and inconsistent -and will change in the future. - -@item -Making side effects happen in the same order as in some other compiler. - -@cindex side effects, order of evaluation -@cindex order of evaluation, side effects -It is never safe to depend on the order of evaluation of side effects. -For example, a function call like this may very well behave differently -from one compiler to another: - -@example -void func (int, int); - -int i = 2; -func (i++, i++); -@end example - -There is no guarantee (in either the C or the C++ standard language -definitions) that the increments will be evaluated in any particular -order. Either increment might happen first. @code{func} might get the -arguments @samp{2, 3}, or it might get @samp{3, 2}, or even @samp{2, 2}. - -@item -Not allowing structures with volatile fields in registers. - -Strictly speaking, there is no prohibition in the ISO C standard -against allowing structures with volatile fields in registers, but -it does not seem to make any sense and is probably not what you wanted -to do. So the compiler will give an error message in this case. - -@item -Making certain warnings into errors by default. - -Some ISO C testsuites report failure when the compiler does not produce -an error message for a certain program. - -@opindex pedantic-errors -ISO C requires a ``diagnostic'' message for certain kinds of invalid -programs, but a warning is defined by GCC to count as a diagnostic. If -GCC produces a warning but not an error, that is correct ISO C support. -If test suites call this ``failure'', they should be run with the GCC -option @option{-pedantic-errors}, which will turn these warnings into -errors. - -@end itemize - -@node Warnings and Errors -@section Warning Messages and Error Messages - -@cindex error messages -@cindex warnings vs errors -@cindex messages, warning and error -The GNU compiler can produce two kinds of diagnostics: errors and -warnings. Each kind has a different purpose: - -@itemize @w{} -@item -@dfn{Errors} report problems that make it impossible to compile your -program. GCC reports errors with the source file name and line -number where the problem is apparent. - -@item -@dfn{Warnings} report other unusual conditions in your code that -@emph{may} indicate a problem, although compilation can (and does) -proceed. Warning messages also report the source file name and line -number, but include the text @samp{warning:} to distinguish them -from error messages. -@end itemize - -Warnings may indicate danger points where you should check to make sure -that your program really does what you intend; or the use of obsolete -features; or the use of nonstandard features of GNU C or C++. Many -warnings are issued only if you ask for them, with one of the @option{-W} -options (for instance, @option{-Wall} requests a variety of useful -warnings). - -@opindex pedantic -@opindex pedantic-errors -GCC always tries to compile your program if possible; it never -gratuitously rejects a program whose meaning is clear merely because -(for instance) it fails to conform to a standard. In some cases, -however, the C and C++ standards specify that certain extensions are -forbidden, and a diagnostic @emph{must} be issued by a conforming -compiler. The @option{-pedantic} option tells GCC to issue warnings in -such cases; @option{-pedantic-errors} says to make them errors instead. -This does not mean that @emph{all} non-ISO constructs get warnings -or errors. - -@xref{Warning Options,,Options to Request or Suppress Warnings}, for -more detail on these and related command-line options. - -@node Bugs -@chapter Reporting Bugs -@cindex bugs -@cindex reporting bugs - -Your bug reports play an essential role in making GCC reliable. - -When you encounter a problem, the first thing to do is to see if it is -already known. @xref{Trouble}. If it isn't known, then you should -report the problem. - -Reporting a bug may help you by bringing a solution to your problem, or -it may not. (If it does not, look in the service directory; see -@ref{Service}.) In any case, the principal function of a bug report is -to help the entire community by making the next version of GCC work -better. Bug reports are your contribution to the maintenance of GCC@. - -Since the maintainers are very overloaded, we cannot respond to every -bug report. However, if the bug has not been fixed, we are likely to -send you a patch and ask you to tell us whether it works. - -In order for a bug report to serve its purpose, you must include the -information that makes for fixing the bug. - -@menu -* Criteria: Bug Criteria. Have you really found a bug? -* Where: Bug Lists. Where to send your bug report. -* Reporting: Bug Reporting. How to report a bug effectively. -* GNATS: gccbug. You can use a bug reporting tool. -* Known: Trouble. Known problems. -* Help: Service. Where to ask for help. -@end menu - -@node Bug Criteria,Bug Lists,,Bugs -@section Have You Found a Bug? -@cindex bug criteria - -If you are not sure whether you have found a bug, here are some guidelines: - -@itemize @bullet -@cindex fatal signal -@cindex core dump -@item -If the compiler gets a fatal signal, for any input whatever, that is a -compiler bug. Reliable compilers never crash. - -@cindex invalid assembly code -@cindex assembly code, invalid -@item -If the compiler produces invalid assembly code, for any input whatever -(except an @code{asm} statement), that is a compiler bug, unless the -compiler reports errors (not just warnings) which would ordinarily -prevent the assembler from being run. - -@cindex undefined behavior -@cindex undefined function value -@cindex increment operators -@item -If the compiler produces valid assembly code that does not correctly -execute the input source code, that is a compiler bug. - -However, you must double-check to make sure, because you may have run -into an incompatibility between GNU C and traditional C -(@pxref{Incompatibilities}). These incompatibilities might be considered -bugs, but they are inescapable consequences of valuable features. - -Or you may have a program whose behavior is undefined, which happened -by chance to give the desired results with another C or C++ compiler. - -For example, in many nonoptimizing compilers, you can write @samp{x;} -at the end of a function instead of @samp{return x;}, with the same -results. But the value of the function is undefined if @code{return} -is omitted; it is not a bug when GCC produces different results. - -Problems often result from expressions with two increment operators, -as in @code{f (*p++, *p++)}. Your previous compiler might have -interpreted that expression the way you intended; GCC might -interpret it another way. Neither compiler is wrong. The bug is -in your code. - -After you have localized the error to a single source line, it should -be easy to check for these things. If your program is correct and -well defined, you have found a compiler bug. - -@item -If the compiler produces an error message for valid input, that is a -compiler bug. - -@cindex invalid input -@item -If the compiler does not produce an error message for invalid input, -that is a compiler bug. However, you should note that your idea of -``invalid input'' might be my idea of ``an extension'' or ``support -for traditional practice''. - -@item -If you are an experienced user of one of the languages GCC supports, your -suggestions for improvement of GCC are welcome in any case. -@end itemize +@include bugreport.texi -@node Bug Lists,Bug Reporting,Bug Criteria,Bugs -@section Where to Report Bugs -@cindex bug report mailing lists -@kindex gcc-bugs@@gcc.gnu.org or bug-gcc@@gnu.org -Send bug reports for the GNU Compiler Collection to -@email{gcc-bugs@@gcc.gnu.org}. In accordance with the GNU-wide -convention, in which bug reports for tool ``foo'' are sent -to @samp{bug-foo@@gnu.org}, the address @email{bug-gcc@@gnu.org} -may also be used; it will forward to the address given above. - -Please read @uref{http://gcc.gnu.org/bugs.html} for additional and/or -more up-to-date bug reporting instructions before you post a bug report. - -@node Bug Reporting,gccbug,Bug Lists,Bugs -@section How to Report Bugs -@cindex compiler bugs, reporting - -The fundamental principle of reporting bugs usefully is this: -@strong{report all the facts}. If you are not sure whether to state a -fact or leave it out, state it! - -Often people omit facts because they think they know what causes the -problem and they conclude that some details don't matter. Thus, you might -assume that the name of the variable you use in an example does not matter. -Well, probably it doesn't, but one cannot be sure. Perhaps the bug is a -stray memory reference which happens to fetch from the location where that -name is stored in memory; perhaps, if the name were different, the contents -of that location would fool the compiler into doing the right thing despite -the bug. Play it safe and give a specific, complete example. That is the -easiest thing for you to do, and the most helpful. - -Keep in mind that the purpose of a bug report is to enable someone to -fix the bug if it is not known. It isn't very important what happens if -the bug is already known. Therefore, always write your bug reports on -the assumption that the bug is not known. - -Sometimes people give a few sketchy facts and ask, ``Does this ring a -bell?'' This cannot help us fix a bug, so it is basically useless. We -respond by asking for enough details to enable us to investigate. -You might as well expedite matters by sending them to begin with. - -Try to make your bug report self-contained. If we have to ask you for -more information, it is best if you include all the previous information -in your response, as well as the information that was missing. - -Please report each bug in a separate message. This makes it easier for -us to track which bugs have been fixed and to forward your bugs reports -to the appropriate maintainer. - -To enable someone to investigate the bug, you should include all these -things: +@include service.texi -@itemize @bullet -@item -The version of GCC@. You can get this by running it with the -@option{-v} option. - -Without this, we won't know whether there is any point in looking for -the bug in the current version of GCC@. - -@item -A complete input file that will reproduce the bug. If the bug is in the -C preprocessor, send a source file and any header files that it -requires. If the bug is in the compiler proper (@file{cc1}), send the -preprocessor output generated by adding @option{-save-temps} to the -compilation command (@pxref{Debugging Options}). When you do this, use -the same @option{-I}, @option{-D} or @option{-U} options that you used in -actual compilation. Then send the @var{input}.i or @var{input}.ii files -generated. - -A single statement is not enough of an example. In order to compile it, -it must be embedded in a complete file of compiler input; and the bug -might depend on the details of how this is done. - -Without a real example one can compile, all anyone can do about your bug -report is wish you luck. It would be futile to try to guess how to -provoke the bug. For example, bugs in register allocation and reloading -frequently depend on every little detail of the function they happen in. - -Even if the input file that fails comes from a GNU program, you should -still send the complete test case. Don't ask the GCC maintainers to -do the extra work of obtaining the program in question---they are all -overworked as it is. Also, the problem may depend on what is in the -header files on your system; it is unreliable for the GCC maintainers -to try the problem with the header files available to them. By sending -CPP output, you can eliminate this source of uncertainty and save us -a certain percentage of wild goose chases. - -@item -The command arguments you gave GCC to compile that example -and observe the bug. For example, did you use @option{-O}? To guarantee -you won't omit something important, list all the options. - -If we were to try to guess the arguments, we would probably guess wrong -and then we would not encounter the bug. - -@item -The type of machine you are using, and the operating system name and -version number. - -@item -The operands you gave to the @code{configure} command when you installed -the compiler. - -@item -A complete list of any modifications you have made to the compiler -source. (We don't promise to investigate the bug unless it happens in -an unmodified compiler. But if you've made modifications and don't tell -us, then you are sending us on a wild goose chase.) - -Be precise about these changes. A description in English is not -enough---send a context diff for them. - -Adding files of your own (such as a machine description for a machine we -don't support) is a modification of the compiler source. - -@item -Details of any other deviations from the standard procedure for installing -GCC@. - -@item -A description of what behavior you observe that you believe is -incorrect. For example, ``The compiler gets a fatal signal,'' or, -``The assembler instruction at line 208 in the output is incorrect.'' - -Of course, if the bug is that the compiler gets a fatal signal, then one -can't miss it. But if the bug is incorrect output, the maintainer might -not notice unless it is glaringly wrong. None of us has time to study -all the assembler code from a 50-line C program just on the chance that -one instruction might be wrong. We need @emph{you} to do this part! - -Even if the problem you experience is a fatal signal, you should still -say so explicitly. Suppose something strange is going on, such as, your -copy of the compiler is out of synch, or you have encountered a bug in -the C library on your system. (This has happened!) Your copy might -crash and the copy here would not. If you @i{said} to expect a crash, -then when the compiler here fails to crash, we would know that the bug -was not happening. If you don't say to expect a crash, then we would -not know whether the bug was happening. We would not be able to draw -any conclusion from our observations. - -If the problem is a diagnostic when compiling GCC with some other -compiler, say whether it is a warning or an error. - -Often the observed symptom is incorrect output when your program is run. -Sad to say, this is not enough information unless the program is short -and simple. None of us has time to study a large program to figure out -how it would work if compiled correctly, much less which line of it was -compiled wrong. So you will have to do that. Tell us which source line -it is, and what incorrect result happens when that line is executed. A -person who understands the program can find this as easily as finding a -bug in the program itself. - -@item -If you send examples of assembler code output from GCC, -please use @option{-g} when you make them. The debugging information -includes source line numbers which are essential for correlating the -output with the input. - -@item -If you wish to mention something in the GCC source, refer to it by -context, not by line number. - -The line numbers in the development sources don't match those in your -sources. Your line numbers would convey no useful information to the -maintainers. - -@item -Additional information from a debugger might enable someone to find a -problem on a machine which he does not have available. However, you -need to think when you collect this information if you want it to have -any chance of being useful. - -@cindex backtrace for bug reports -For example, many people send just a backtrace, but that is never -useful by itself. A simple backtrace with arguments conveys little -about GCC because the compiler is largely data-driven; the same -functions are called over and over for different RTL insns, doing -different things depending on the details of the insn. - -Most of the arguments listed in the backtrace are useless because they -are pointers to RTL list structure. The numeric values of the -pointers, which the debugger prints in the backtrace, have no -significance whatever; all that matters is the contents of the objects -they point to (and most of the contents are other such pointers). - -In addition, most compiler passes consist of one or more loops that -scan the RTL insn sequence. The most vital piece of information about -such a loop---which insn it has reached---is usually in a local variable, -not in an argument. - -@findex debug_rtx -What you need to provide in addition to a backtrace are the values of -the local variables for several stack frames up. When a local -variable or an argument is an RTX, first print its value and then use -the GDB command @code{pr} to print the RTL expression that it points -to. (If GDB doesn't run on your machine, use your debugger to call -the function @code{debug_rtx} with the RTX as an argument.) In -general, whenever a variable is a pointer, its value is no use -without the data it points to. -@end itemize - -Here are some things that are not necessary: - -@itemize @bullet -@item -A description of the envelope of the bug. - -Often people who encounter a bug spend a lot of time investigating -which changes to the input file will make the bug go away and which -changes will not affect it. - -This is often time consuming and not very useful, because the way we -will find the bug is by running a single example under the debugger with -breakpoints, not by pure deduction from a series of examples. You might -as well save your time for something else. - -Of course, if you can find a simpler example to report @emph{instead} of -the original one, that is a convenience. Errors in the output will be -easier to spot, running under the debugger will take less time, etc. -Most GCC bugs involve just one function, so the most straightforward -way to simplify an example is to delete all the function definitions -except the one where the bug occurs. Those earlier in the file may be -replaced by external declarations if the crucial function depends on -them. (Exception: inline functions may affect compilation of functions -defined later in the file.) - -However, simplification is not vital; if you don't want to do this, -report the bug anyway and send the entire test case you used. - -@item -In particular, some people insert conditionals @samp{#ifdef BUG} around -a statement which, if removed, makes the bug not happen. These are just -clutter; we won't pay any attention to them anyway. Besides, you should -send us cpp output, and that can't have conditionals. - -@item -A patch for the bug. - -A patch for the bug is useful if it is a good one. But don't omit the -necessary information, such as the test case, on the assumption that a -patch is all we need. We might see problems with your patch and decide -to fix the problem another way, or we might not understand it at all. - -Sometimes with a program as complicated as GCC it is very hard to -construct an example that will make the program follow a certain path -through the code. If you don't send the example, we won't be able to -construct one, so we won't be able to verify that the bug is fixed. - -And if we can't understand what bug you are trying to fix, or why your -patch should be an improvement, we won't install it. A test case will -help us to understand. - -See @uref{http://gcc.gnu.org/contribute.html} -for guidelines on how to make it easy for us to -understand and install your patches. - -@item -A guess about what the bug is or what it depends on. - -Such guesses are usually wrong. Even I can't guess right about such -things without first using the debugger to find the facts. - -@item -A core dump file. - -We have no way of examining a core dump for your type of machine -unless we have an identical system---and if we do have one, -we should be able to reproduce the crash ourselves. -@end itemize - -@node gccbug,, Bug Reporting, Bugs -@section The gccbug script -@cindex gccbug script - -To simplify creation of bug reports, and to allow better tracking of -reports, we use the GNATS bug tracking system. Part of that system is -the @code{gccbug} script. This is a Unix shell script, so you need a -shell to run it. It is normally installed in the same directory where -@code{gcc} is installed. - -The gccbug script is derived from send-pr, @pxref{using -send-pr,,Creating new Problem Reports,send-pr,Reporting Problems}. When -invoked, it starts a text editor so you can fill out the various fields -of the report. When the you quit the editor, the report is automatically -send to the bug reporting address. - -A number of fields in this bug report form are specific to GCC, and are -explained at @uref{http://gcc.gnu.org/gnats.html}. - -@node Service -@chapter How To Get Help with GCC - -If you need help installing, using or changing GCC, there are two -ways to find it: - -@itemize @bullet -@item -Send a message to a suitable network mailing list. First try -@email{gcc-help@@gcc.gnu.org} (for help installing or using GCC), and if -that brings no response, try @email{gcc@@gcc.gnu.org}. For help -changing GCC, ask @email{gcc@@gcc.gnu.org}. If you think you have found -a bug in GCC, please report it following the instructions at -@pxref{Bug Reporting}. - -@item -Look in the service directory for someone who might help you for a fee. -The service directory is found at -@uref{http://www.gnu.org/prep/service.html}. -@end itemize - -@c For further information, see -@c @uref{http://gcc.gnu.org/cgi-bin/fom.cgi?file=12}. -@c FIXME: this URL may be too volatile, this FAQ entry needs to move to -@c the regular web pages before we can uncomment the reference. - -@node Contributing -@chapter Contributing to GCC Development - -If you would like to help pretest GCC releases to assure they work well, -our current development sources are available by CVS (see -@uref{http://gcc.gnu.org/cvs.html}). Source and binary snapshots are -also available for FTP; see @uref{http://gcc.gnu.org/snapshots.html}. - -If you would like to work on improvements to GCC, please read the -advice at these URLs: - -@smallexample -@uref{http://gcc.gnu.org/contribute.html} -@uref{http://gcc.gnu.org/contributewhy.html} -@end smallexample - -@noindent -for information on how to make useful contributions and avoid -duplication of effort. Suggested projects are listed at -@uref{http://gcc.gnu.org/projects/}. - -@node VMS -@chapter Using GCC on VMS - -@c prevent bad page break with this line -Here is how to use GCC on VMS@. - -@menu -* Include Files and VMS:: Where the preprocessor looks for the include files. -* Global Declarations:: How to do globaldef, globalref and globalvalue with - GCC. -* VMS Misc:: Misc information. -@end menu - -@node Include Files and VMS -@section Include Files and VMS - -@cindex include files and VMS -@cindex VMS and include files -@cindex header files and VMS -Due to the differences between the filesystems of Unix and VMS, GCC -attempts to translate file names in @samp{#include} into names that VMS -will understand. The basic strategy is to prepend a prefix to the -specification of the include file, convert the whole filename to a VMS -filename, and then try to open the file. GCC tries various prefixes -one by one until one of them succeeds: - -@enumerate -@item -The first prefix is the @samp{GNU_CC_INCLUDE:} logical name: this is -where GNU C header files are traditionally stored. If you wish to store -header files in non-standard locations, then you can assign the logical -@samp{GNU_CC_INCLUDE} to be a search list, where each element of the -list is suitable for use with a rooted logical. - -@item -The next prefix tried is @samp{SYS$SYSROOT:[SYSLIB.]}. This is where -VAX-C header files are traditionally stored. - -@item -If the include file specification by itself is a valid VMS filename, the -preprocessor then uses this name with no prefix in an attempt to open -the include file. - -@item -If the file specification is not a valid VMS filename (i.e.@: does not -contain a device or a directory specifier, and contains a @samp{/} -character), the preprocessor tries to convert it from Unix syntax to -VMS syntax. - -Conversion works like this: the first directory name becomes a device, -and the rest of the directories are converted into VMS-format directory -names. For example, the name @file{X11/foobar.h} is -translated to @file{X11:[000000]foobar.h} or @file{X11:foobar.h}, -whichever one can be opened. This strategy allows you to assign a -logical name to point to the actual location of the header files. - -@item -If none of these strategies succeeds, the @samp{#include} fails. -@end enumerate - -Include directives of the form: - -@example -#include foobar -@end example - -@noindent -are a common source of incompatibility between VAX-C and GCC@. VAX-C -treats this much like a standard @code{#include <foobar.h>} directive. -That is incompatible with the ISO C behavior implemented by GCC: to -expand the name @code{foobar} as a macro. Macro expansion should -eventually yield one of the two standard formats for @code{#include}: - -@example -#include "@var{file}" -#include <@var{file}> -@end example - -If you have this problem, the best solution is to modify the source to -convert the @code{#include} directives to one of the two standard forms. -That will work with either compiler. If you want a quick and dirty fix, -define the file names as macros with the proper expansion, like this: - -@example -#define stdio <stdio.h> -@end example - -@noindent -This will work, as long as the name doesn't conflict with anything else -in the program. - -Another source of incompatibility is that VAX-C assumes that: - -@example -#include "foobar" -@end example - -@noindent -is actually asking for the file @file{foobar.h}. GCC does not -make this assumption, and instead takes what you ask for literally; -it tries to read the file @file{foobar}. The best way to avoid this -problem is to always specify the desired file extension in your include -directives. - -GCC for VMS is distributed with a set of include files that is -sufficient to compile most general purpose programs. Even though the -GCC distribution does not contain header files to define constants -and structures for some VMS system-specific functions, there is no -reason why you cannot use GCC with any of these functions. You first -may have to generate or create header files, either by using the public -domain utility @code{UNSDL} (which can be found on a DECUS tape), or by -extracting the relevant modules from one of the system macro libraries, -and using an editor to construct a C header file. - -A @code{#include} file name cannot contain a DECNET node name. The -preprocessor reports an I/O error if you attempt to use a node name, -whether explicitly, or implicitly via a logical name. - -@node Global Declarations -@section Global Declarations and VMS - -@findex GLOBALREF -@findex GLOBALDEF -@findex GLOBALVALUEDEF -@findex GLOBALVALUEREF -GCC does not provide the @code{globalref}, @code{globaldef} and -@code{globalvalue} keywords of VAX-C@. You can get the same effect with -an obscure feature of GAS, the GNU assembler. (This requires GAS -version 1.39 or later.) The following macros allow you to use this -feature in a fairly natural way: - -@smallexample -#ifdef __GNUC__ -#define GLOBALREF(TYPE,NAME) \ - TYPE NAME \ - asm ("_$$PsectAttributes_GLOBALSYMBOL$$" #NAME) -#define GLOBALDEF(TYPE,NAME,VALUE) \ - TYPE NAME \ - asm ("_$$PsectAttributes_GLOBALSYMBOL$$" #NAME) \ - = VALUE -#define GLOBALVALUEREF(TYPE,NAME) \ - const TYPE NAME[1] \ - asm ("_$$PsectAttributes_GLOBALVALUE$$" #NAME) -#define GLOBALVALUEDEF(TYPE,NAME,VALUE) \ - const TYPE NAME[1] \ - asm ("_$$PsectAttributes_GLOBALVALUE$$" #NAME) \ - = @{VALUE@} -#else -#define GLOBALREF(TYPE,NAME) \ - globalref TYPE NAME -#define GLOBALDEF(TYPE,NAME,VALUE) \ - globaldef TYPE NAME = VALUE -#define GLOBALVALUEDEF(TYPE,NAME,VALUE) \ - globalvalue TYPE NAME = VALUE -#define GLOBALVALUEREF(TYPE,NAME) \ - globalvalue TYPE NAME -#endif -@end smallexample - -@noindent -(The @code{_$$PsectAttributes_GLOBALSYMBOL} prefix at the start of the -name is removed by the assembler, after it has modified the attributes -of the symbol). These macros are provided in the VMS binaries -distribution in a header file @file{GNU_HACKS.H}. An example of the -usage is: - -@example -GLOBALREF (int, ijk); -GLOBALDEF (int, jkl, 0); -@end example - -The macros @code{GLOBALREF} and @code{GLOBALDEF} cannot be used -straightforwardly for arrays, since there is no way to insert the array -dimension into the declaration at the right place. However, you can -declare an array with these macros if you first define a typedef for the -array type, like this: - -@example -typedef int intvector[10]; -GLOBALREF (intvector, foo); -@end example - -Array and structure initializers will also break the macros; you can -define the initializer to be a macro of its own, or you can expand the -@code{GLOBALDEF} macro by hand. You may find a case where you wish to -use the @code{GLOBALDEF} macro with a large array, but you are not -interested in explicitly initializing each element of the array. In -such cases you can use an initializer like: @code{@{0,@}}, which will -initialize the entire array to @code{0}. - -A shortcoming of this implementation is that a variable declared with -@code{GLOBALVALUEREF} or @code{GLOBALVALUEDEF} is always an array. For -example, the declaration: - -@example -GLOBALVALUEREF(int, ijk); -@end example - -@noindent -declares the variable @code{ijk} as an array of type @code{int [1]}. -This is done because a globalvalue is actually a constant; its ``value'' -is what the linker would normally consider an address. That is not how -an integer value works in C, but it is how an array works. So treating -the symbol as an array name gives consistent results---with the -exception that the value seems to have the wrong type. @strong{Don't -try to access an element of the array.} It doesn't have any elements. -The array ``address'' may not be the address of actual storage. - -The fact that the symbol is an array may lead to warnings where the -variable is used. Insert type casts to avoid the warnings. Here is an -example; it takes advantage of the ISO C feature allowing macros that -expand to use the same name as the macro itself. - -@example -GLOBALVALUEREF (int, ss$_normal); -GLOBALVALUEDEF (int, xyzzy,123); -#ifdef __GNUC__ -#define ss$_normal ((int) ss$_normal) -#define xyzzy ((int) xyzzy) -#endif -@end example - -Don't use @code{globaldef} or @code{globalref} with a variable whose -type is an enumeration type; this is not implemented. Instead, make the -variable an integer, and use a @code{globalvaluedef} for each of the -enumeration values. An example of this would be: - -@example -#ifdef __GNUC__ -GLOBALDEF (int, color, 0); -GLOBALVALUEDEF (int, RED, 0); -GLOBALVALUEDEF (int, BLUE, 1); -GLOBALVALUEDEF (int, GREEN, 3); -#else -enum globaldef color @{RED, BLUE, GREEN = 3@}; -#endif -@end example - -@node VMS Misc -@section Other VMS Issues - -@cindex exit status and VMS -@cindex return value of @code{main} -@cindex @code{main} and the exit status -GCC automatically arranges for @code{main} to return 1 by default if -you fail to specify an explicit return value. This will be interpreted -by VMS as a status code indicating a normal successful completion. -Version 1 of GCC did not provide this default. - -GCC on VMS works only with the GNU assembler, GAS@. You need version -1.37 or later of GAS in order to produce value debugging information for -the VMS debugger. Use the ordinary VMS linker with the object files -produced by GAS@. - -@cindex shared VMS run time system -@cindex @file{VAXCRTL} -Under previous versions of GCC, the generated code would occasionally -give strange results when linked to the sharable @file{VAXCRTL} library. -Now this should work. - -A caveat for use of @code{const} global variables: the @code{const} -modifier must be specified in every external declaration of the variable -in all of the source files that use that variable. Otherwise the linker -will issue warnings about conflicting attributes for the variable. Your -program will still work despite the warnings, but the variable will be -placed in writable storage. - -@cindex name augmentation -@cindex case sensitivity and VMS -@cindex VMS and case sensitivity -Although the VMS linker does distinguish between upper and lower case -letters in global symbols, most VMS compilers convert all such symbols -into upper case and most run-time library routines also have upper case -names. To be able to reliably call such routines, GCC (by means of -the assembler GAS) converts global symbols into upper case like other -VMS compilers. However, since the usual practice in C is to distinguish -case, GCC (via GAS) tries to preserve usual C behavior by augmenting -each name that is not all lower case. This means truncating the name -to at most 23 characters and then adding more characters at the end -which encode the case pattern of those 23. Names which contain at -least one dollar sign are an exception; they are converted directly into -upper case without augmentation. - -Name augmentation yields bad results for programs that use precompiled -libraries (such as Xlib) which were generated by another compiler. You -can use the compiler option @samp{/NOCASE_HACK} to inhibit augmentation; -it makes external C functions and variables case-independent as is usual -on VMS@. Alternatively, you could write all references to the functions -and variables in such libraries using lower case; this will work on VMS, -but is not portable to other systems. The compiler option @samp{/NAMES} -also provides control over global name handling. - -Function and variable names are handled somewhat differently with G++. -The GNU C++ compiler performs @dfn{name mangling} on function -names, which means that it adds information to the function name to -describe the data types of the arguments that the function takes. One -result of this is that the name of a function can become very long. -Since the VMS linker only recognizes the first 31 characters in a name, -special action is taken to ensure that each function and variable has a -unique name that can be represented in 31 characters. - -If the name (plus a name augmentation, if required) is less than 32 -characters in length, then no special action is performed. If the name -is longer than 31 characters, the assembler (GAS) will generate a -hash string based upon the function name, truncate the function name to -23 characters, and append the hash string to the truncated name. If the -@samp{/VERBOSE} compiler option is used, the assembler will print both -the full and truncated names of each symbol that is truncated. - -The @samp{/NOCASE_HACK} compiler option should not be used when you are -compiling programs that use libg++. libg++ has several instances of -objects (i.e. @code{Filebuf} and @code{filebuf}) which become -indistinguishable in a case-insensitive environment. This leads to -cases where you need to inhibit augmentation selectively (if you were -using libg++ and Xlib in the same program, for example). There is no -special feature for doing this, but you can get the result by defining a -macro for each mixed case symbol for which you wish to inhibit -augmentation. The macro should expand into the lower case equivalent of -itself. For example: - -@example -#define StuDlyCapS studlycaps -@end example +@include contribute.texi -These macro definitions can be placed in a header file to minimize the -number of changes to your source code. +@include vms.texi @node Makefile @chapter Additional Makefile and configure information. |