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Diffstat (limited to 'lib/hipe/llvm/elf_format.erl')
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diff --git a/lib/hipe/llvm/elf_format.erl b/lib/hipe/llvm/elf_format.erl new file mode 100644 index 0000000000..8cf6ea6250 --- /dev/null +++ b/lib/hipe/llvm/elf_format.erl @@ -0,0 +1,620 @@ +%% -*- erlang-indent-level: 2 -*- + +%%% @copyright 2011-2014 Yiannis Tsiouris <gtsiour@softlab.ntua.gr>, +%%% Chris Stavrakakis <hydralisk.r@gmail.com>, +%%% Kostis Sagonas <kostis@cs.ntua.gr> +%%% @author Yiannis Tsiouris <gtsiour@softlab.ntua.gr> +%%% [http://www.softlab.ntua.gr/~gtsiour/] + +%%% @doc This module contains functions for extracting various pieces of +%%% information from an ELF formated Object file. To fully understand +%%% the ELF format and the use of these functions please read +%%% "[http://www.linuxjournal.com/article/1060?page=0,0]" carefully. + +-module(elf_format). + +-export([%% Relocations + extract_rela/2, + %% Note + extract_note/2, + %% Executable code + extract_text/1, + %% GCC Exception Table + get_exn_handlers/1, + %% Symbols + elf_symbols/1, + %% Sections + section_contents/2, + %% Main interface + read/1 + ]). + +-include("elf_format.hrl"). + +%%------------------------------------------------------------------------------ +%% Types +%%------------------------------------------------------------------------------ + +-export_type([elf/0 + ,addend/0 + ,bitflags/0 + ,name/0 + ,offset/0 + ,reloc_type/0 + ,shdr_type/0 + ,size/0 + ,sym_bind/0 + ,sym_type/0 + ,valueoff/0 + ]). + +-type bitflags() :: non_neg_integer(). +-type index() :: non_neg_integer(). +-type lp() :: non_neg_integer(). % landing pad +-type num() :: non_neg_integer(). +-type offset() :: non_neg_integer(). +-type size() :: non_neg_integer(). +-type start() :: non_neg_integer(). + +-type addend() :: integer() | undefined. +-type name() :: string(). +-type shdr_type() :: 'null' | 'progbits' | 'symtab' | 'strtab' | 'rela' + | 'hash' | 'dynamic' | 'note' | 'nobits' | 'rel' | 'shlib' + | 'dynsym' | {os, ?SHT_LOOS..?SHT_HIOS} + | {proc, ?SHT_LOPROC..?SHT_HIPROC}. +-type sym_bind() :: 'local' | 'global' | 'weak' | {os, ?STB_LOOS..?STB_HIOS} + | {proc, ?STB_LOPROC..?STB_HIPROC}. +-type sym_type() :: 'notype' | 'object' | 'func' | 'section' | 'file' + | {os, ?STT_LOOS..?STT_HIOS} + | {proc, ?STT_LOPROC..?STT_HIPROC}. +-type valueoff() :: offset(). + +-ifdef(BIT32). % 386 +-type reloc_type() :: '32' | 'pc32'. +-else. % X86_64 +-type reloc_type() :: '64' | 'pc32' | '32'. +-endif. + +%%------------------------------------------------------------------------------ +%% Abstract Data Types and Accessors for ELF Structures. +%%------------------------------------------------------------------------------ + +-record(elf, {file :: binary() + ,sections :: [elf_shdr()] + ,sec_nam :: #{string() => elf_shdr()} + ,symbols :: undefined | [elf_sym()] + }). +-opaque elf() :: #elf{}. + +%% File header +-record(elf_ehdr, {ident, % ELF identification + type, % Object file type + machine, % Machine Type + version, % Object file version + entry, % Entry point address + phoff, % Program header offset + shoff :: offset(), % Section header offset + flags, % Processor-specific flags + ehsize :: size(), % ELF header size + phentsize :: size(), % Size of program header entry + phnum :: num(), % Number of program header entries + shentsize :: size(), % Size of section header entry + shnum :: num(), % Number of section header entries + shstrndx :: index() % Section name string table index + }). +-type elf_ehdr() :: #elf_ehdr{}. + +-record(elf_ehdr_ident, {class, % File class + data, % Data encoding + version, % File version + osabi, % OS/ABI identification + abiversion, % ABI version + pad, % Start of padding bytes + nident % Size of e_ident[] + }). +%% -type elf_ehdr_ident() :: #elf_ehdr_ident{}. + +%% %% Program header table +%% -record(elf_phdr, {type, % Type of segment +%% flags, % Segment attributes +%% offset, % Offset in file +%% vaddr, % Virtual address in memory +%% paddr, % Reserved +%% filesz, % Size of segment in file +%% memsz, % Size of segment in memory +%% align % Alignment of segment +%% }). + +%% %% GCC exception table +%% -record(elf_gccexntab, {lpbenc, % Landing pad base encoding +%% lpbase, % Landing pad base +%% ttenc, % Type table encoding +%% ttoff, % Type table offset +%% csenc, % Call-site table encoding +%% cstabsize, % Call-site table size +%% cstab :: cstab() % Call-site table +%% }). +%% -type elf_gccexntab() :: #elf_gccexntab{}. + +-record(elf_gccexntab_callsite, {start :: start(), % Call-site start + size :: size(), % Call-site size + lp :: lp(), % Call-site landing pad + % (exception handler) + onaction % On action (e.g. cleanup) + }). +%% -type elf_gccexntab_callsite() :: #elf_gccexntab_callsite{}. + +%%------------------------------------------------------------------------------ +%% Accessor Functions +%%------------------------------------------------------------------------------ + +%% File header +%% -spec mk_ehdr(...) -> elf_ehrd(). +mk_ehdr(Ident, Type, Machine, Version, Entry, Phoff, Shoff, Flags, Ehsize, + Phentsize, Phnum, Shentsize, Shnum, Shstrndx) -> + #elf_ehdr{ident = Ident, type = Type, machine = Machine, version = Version, + entry = Entry, phoff = Phoff, shoff = Shoff, flags = Flags, + ehsize = Ehsize, phentsize = Phentsize, phnum = Phnum, + shentsize = Shentsize, shnum = Shnum, shstrndx = Shstrndx}. + +%% -spec ehdr_shoff(elf_ehdr()) -> offset(). +%% ehdr_shoff(#elf_ehdr{shoff = Offset}) -> Offset. +%% +%% -spec ehdr_shentsize(elf_ehdr()) -> size(). +%% ehdr_shentsize(#elf_ehdr{shentsize = Size}) -> Size. +%% +%% -spec ehdr_shnum(elf_ehdr()) -> num(). +%% ehdr_shnum(#elf_ehdr{shnum = Num}) -> Num. +%% +%% -spec ehdr_shstrndx(elf_ehdr()) -> index(). +%% ehdr_shstrndx(#elf_ehdr{shstrndx = Index}) -> Index. + + +%%-spec mk_ehdr_ident(...) -> elf_ehdr_ident(). +mk_ehdr_ident(Class, Data, Version, OsABI, AbiVersion, Pad, Nident) -> + #elf_ehdr_ident{class = Class, data = Data, version = Version, osabi = OsABI, + abiversion = AbiVersion, pad = Pad, nident = Nident}. + +%%%------------------------- +%%% Section header entries +%%%------------------------- +mk_shdr(Name, Type, Flags, Addr, Offset, Size, Link, Info, AddrAlign, EntSize) -> + #elf_shdr{name = Name, type = Type, flags = Flags, addr = Addr, + offset = Offset, size = Size, link = Link, info = Info, + addralign = AddrAlign, entsize = EntSize}. + +%% -spec shdr_offset(elf_shdr()) -> offset(). +%% shdr_offset(#elf_shdr{offset = Offset}) -> Offset. +%% +%% -spec shdr_size(elf_shdr()) -> size(). +%% shdr_size(#elf_shdr{size = Size}) -> Size. + +%%%------------------------- +%%% Symbol Table Entries +%%%------------------------- +mk_sym(Name, Bind, Type, Section, Value, Size) -> + #elf_sym{name = Name, bind = Bind, type = Type, + section = Section, value = Value, size = Size}. + +%% -spec sym_name(elf_sym()) -> string(). +%% sym_name(#elf_sym{name = Name}) -> Name. +%% +%% -spec sym_value(elf_sym()) -> valueoff(). +%% sym_value(#elf_sym{value = Value}) -> Value. +%% +%% -spec sym_size(elf_sym()) -> size(). +%% sym_size(#elf_sym{size = Size}) -> Size. + +%% %%%------------------------- +%% %%% GCC exception table +%% %%%------------------------- +%% -type cstab() :: [elf_gccexntab_callsite()]. +%% +%% mk_gccexntab(LPbenc, LPbase, TTenc, TToff, CSenc, CStabsize, CStab) -> +%% #elf_gccexntab{lpbenc = LPbenc, lpbase = LPbase, ttenc = TTenc, +%% ttoff = TToff, csenc = CSenc, cstabsize = CStabsize, +%% cstab = CStab}. +%% +%% -spec gccexntab_cstab(elf_gccexntab()) -> cstab(). +%% gccexntab_cstab(#elf_gccexntab{cstab = CSTab}) -> CSTab. + +mk_gccexntab_callsite(Start, Size, LP, Action) -> + #elf_gccexntab_callsite{start = Start, size=Size, lp=LP, onaction=Action}. + +%% -spec gccexntab_callsite_start(elf_gccexntab_callsite()) -> start(). +%% gccexntab_callsite_start(#elf_gccexntab_callsite{start = Start}) -> Start. +%% +%% -spec gccexntab_callsite_size(elf_gccexntab_callsite()) -> size(). +%% gccexntab_callsite_size(#elf_gccexntab_callsite{size = Size}) -> Size. +%% +%% -spec gccexntab_callsite_lp(elf_gccexntab_callsite()) -> lp(). +%% gccexntab_callsite_lp(#elf_gccexntab_callsite{lp = LP}) -> LP. + +%%------------------------------------------------------------------------------ +%% Main interface function +%%------------------------------------------------------------------------------ + +%% @doc Parses an ELF file. +-spec read(binary()) -> elf(). +read(ElfBin) -> + Header = extract_header(ElfBin), + [_UndefinedSec|Sections] = extract_shdrtab(ElfBin, Header), + SecNam = maps:from_list( + [{Name, Sec} || Sec = #elf_shdr{name=Name} <- Sections]), + Elf0 = #elf{file=ElfBin, sections=Sections, sec_nam=SecNam}, + [_UndefinedSym|Symbols] = extract_symtab(Elf0, extract_strtab(Elf0)), + Elf0#elf{symbols=Symbols}. + +%%------------------------------------------------------------------------------ +%% Functions to manipulate the ELF File Header +%%------------------------------------------------------------------------------ + +%% @doc Extracts the File Header from an ELF formatted object file. Also sets +%% the ELF class variable in the process dictionary (used by many functions +%% in this and hipe_llvm_main modules). +-spec extract_header(binary()) -> elf_ehdr(). +extract_header(ElfBin) -> + Ehdr_bin = get_binary_segment(ElfBin, 0, ?ELF_EHDR_SIZE), + << %% Structural pattern matching on fields. + Ident_bin:?E_IDENT_SIZE/binary, + Type:?bits(?E_TYPE_SIZE)/integer-little, + Machine:?bits(?E_MACHINE_SIZE)/integer-little, + Version:?bits(?E_VERSION_SIZE)/integer-little, + Entry:?bits(?E_ENTRY_SIZE)/integer-little, + Phoff:?bits(?E_PHOFF_SIZE)/integer-little, + Shoff:?bits(?E_SHOFF_SIZE)/integer-little, + Flags:?bits(?E_FLAGS_SIZE)/integer-little, + Ehsize:?bits(?E_EHSIZE_SIZE)/integer-little, + Phentsize:?bits(?E_PHENTSIZE_SIZE)/integer-little, + Phnum:?bits(?E_PHNUM_SIZE)/integer-little, + Shentsize:?bits(?E_SHENTSIZE_SIZE)/integer-little, + Shnum:?bits(?E_SHENTSIZE_SIZE)/integer-little, + Shstrndx:?bits(?E_SHSTRNDX_SIZE)/integer-little + >> = Ehdr_bin, + <<16#7f, $E, $L, $F, Class, Data, Version, Osabi, Abiversion, + Pad:6/binary, Nident + >> = Ident_bin, + Ident = mk_ehdr_ident(Class, Data, Version, Osabi, + Abiversion, Pad, Nident), + mk_ehdr(Ident, Type, Machine, Version, Entry, Phoff, Shoff, Flags, + Ehsize, Phentsize, Phnum, Shentsize, Shnum, Shstrndx). + +%%------------------------------------------------------------------------------ +%% Functions to manipulate Section Header Entries +%%------------------------------------------------------------------------------ + +-type shdrtab() :: [elf_shdr()]. + +%% @doc Extracts the Section Header Table from an ELF formated Object File. +-spec extract_shdrtab(binary(), elf_ehdr()) -> shdrtab(). +extract_shdrtab(ElfBin, #elf_ehdr{shoff=ShOff, shentsize=?ELF_SHDRENTRY_SIZE, + shnum=ShNum, shstrndx=ShStrNdx}) -> + %% Get actual Section header table (binary) + ShdrBin = get_binary_segment(ElfBin, ShOff, ShNum * ?ELF_SHDRENTRY_SIZE), + %% We need to lookup the offset and size of the section header string table + %% before we can fully parse the section table. We compute its offset and + %% extract the fields we need here. + ShStrEntryOffset = ShStrNdx * ?ELF_SHDRENTRY_SIZE, + <<_:ShStrEntryOffset/binary, _:?SH_NAME_SIZE/binary, + _:?SH_TYPE_SIZE/binary, _:?SH_FLAGS_SIZE/binary, _:?SH_ADDR_SIZE/binary, + ShStrOffset:?bits(?SH_OFFSET_SIZE)/little, + ShStrSize:?bits(?SH_SIZE_SIZE)/little, + _/binary>> = ShdrBin, + ShStrTab = parse_strtab(get_binary_segment(ElfBin, ShStrOffset, ShStrSize)), + get_shdrtab_entries(ShdrBin, ShStrTab). + +get_shdrtab_entries(<<>>, _ShStrTab) -> []; +get_shdrtab_entries(ShdrTab, ShStrTab) -> + <<%% Structural pattern matching on fields. + Name:?bits(?SH_NAME_SIZE)/integer-little, + Type:?bits(?SH_TYPE_SIZE)/integer-little, + Flags:?bits(?SH_FLAGS_SIZE)/integer-little, + Addr:?bits(?SH_ADDR_SIZE)/integer-little, + Offset:?bits(?SH_OFFSET_SIZE)/integer-little, + Size:?bits(?SH_SIZE_SIZE)/integer-little, + Link:?bits(?SH_LINK_SIZE)/integer-little, + Info:?bits(?SH_INFO_SIZE)/integer-little, + Addralign:?bits(?SH_ADDRALIGN_SIZE)/integer-little, + Entsize:?bits(?SH_ENTSIZE_SIZE)/integer-little, + Rest/binary + >> = ShdrTab, + Entry = mk_shdr(get_strtab_entry(Name, ShStrTab), decode_shdr_type(Type), + Flags, Addr, Offset, Size, Link, Info, Addralign, Entsize), + [Entry | get_shdrtab_entries(Rest, ShStrTab)]. + +decode_shdr_type(?SHT_NULL) -> 'null'; +decode_shdr_type(?SHT_PROGBITS) -> 'progbits'; +decode_shdr_type(?SHT_SYMTAB) -> 'symtab'; +decode_shdr_type(?SHT_STRTAB) -> 'strtab'; +decode_shdr_type(?SHT_RELA) -> 'rela'; +decode_shdr_type(?SHT_HASH) -> 'hash'; %unused +decode_shdr_type(?SHT_DYNAMIC) -> 'dynamic'; %unused +decode_shdr_type(?SHT_NOTE) -> 'note'; %unused +decode_shdr_type(?SHT_NOBITS) -> 'nobits'; +decode_shdr_type(?SHT_REL) -> 'rel'; +decode_shdr_type(?SHT_SHLIB) -> 'shlib'; %unused +decode_shdr_type(?SHT_DYNSYM) -> 'dynsym'; %unused +decode_shdr_type(OS) when ?SHT_LOOS =< OS, OS =< ?SHT_HIOS -> {os, OS}; +decode_shdr_type(Proc) when ?SHT_LOPROC =< Proc, Proc =< ?SHT_HIPROC -> + {proc, Proc}. + +-spec elf_section(non_neg_integer(), elf()) -> undefined | abs | elf_shdr(). +elf_section(0, #elf{}) -> undefined; +elf_section(?SHN_ABS, #elf{}) -> abs; +elf_section(Index, #elf{sections=SecIdx}) -> + lists:nth(Index, SecIdx). + +%% Reads the contents of a section from an object +-spec section_contents(elf_shdr(), elf()) -> binary(). +section_contents(#elf_shdr{offset=Offset, size=Size}, #elf{file=ElfBin}) -> + get_binary_segment(ElfBin, Offset, Size). + +%%------------------------------------------------------------------------------ +%% Functions to manipulate Symbol Table +%%------------------------------------------------------------------------------ + +%% @doc Function that extracts Symbol Table from an ELF Object file. +extract_symtab(Elf, StrTab) -> + Symtab = extract_segment_by_name(Elf, ?SYMTAB), + [parse_sym(Sym, Elf, StrTab) || <<Sym:?ELF_SYM_SIZE/binary>> <= Symtab]. + +-ifdef(BIT32). +parse_sym(<<%% Structural pattern matching on fields. + Name:?bits(?ST_NAME_SIZE)/integer-little, + Value:?bits(?ST_VALUE_SIZE)/integer-little, + Size:?bits(?ST_SIZE_SIZE)/integer-little, + Info:?bits(?ST_INFO_SIZE)/integer-little, + _Other:?bits(?ST_OTHER_SIZE)/integer-little, + Shndx:?bits(?ST_SHNDX_SIZE)/integer-little>>, + Elf, StrTab) -> + mk_sym(get_strtab_entry(Name, StrTab), decode_symbol_bind(?ELF_ST_BIND(Info)), + decode_symbol_type(?ELF_ST_TYPE(Info)), elf_section(Shndx, Elf), Value, + Size). +-else. +parse_sym(<<%% Same fields in different order: + Name:?bits(?ST_NAME_SIZE)/integer-little, + Info:?bits(?ST_INFO_SIZE)/integer-little, + _Other:?bits(?ST_OTHER_SIZE)/integer-little, + Shndx:?bits(?ST_SHNDX_SIZE)/integer-little, + Value:?bits(?ST_VALUE_SIZE)/integer-little, + Size:?bits(?ST_SIZE_SIZE)/integer-little>>, + Elf, StrTab) -> + mk_sym(get_strtab_entry(Name, StrTab), decode_symbol_bind(?ELF_ST_BIND(Info)), + decode_symbol_type(?ELF_ST_TYPE(Info)), elf_section(Shndx, Elf), Value, + Size). +-endif. + +decode_symbol_bind(?STB_LOCAL) -> 'local'; +decode_symbol_bind(?STB_GLOBAL) -> 'global'; +decode_symbol_bind(?STB_WEAK) -> 'weak'; %unused +decode_symbol_bind(OS) when ?STB_LOOS =< OS, OS =< ?STB_HIOS -> {os, OS}; +decode_symbol_bind(Proc) when ?STB_LOPROC =< Proc, Proc =< ?STB_HIPROC -> + {proc, Proc}. + +decode_symbol_type(?STT_NOTYPE) -> 'notype'; +decode_symbol_type(?STT_OBJECT) -> 'object'; +decode_symbol_type(?STT_FUNC) -> 'func'; +decode_symbol_type(?STT_SECTION) -> 'section'; +decode_symbol_type(?STT_FILE) -> 'file'; +decode_symbol_type(OS) when ?STT_LOOS =< OS, OS =< ?STT_HIOS -> {os, OS}; +decode_symbol_type(Proc) when ?STT_LOPROC =< Proc, Proc =< ?STT_HIPROC -> + {proc, Proc}. + +%% @doc Extracts a specific entry from the Symbol Table. +-spec elf_symbol(0, elf()) -> undefined; + (pos_integer(), elf()) -> elf_sym(). +elf_symbol(0, #elf{}) -> undefined; +elf_symbol(Index, #elf{symbols=Symbols}) -> lists:nth(Index, Symbols). + +-spec elf_symbols(elf()) -> [elf_sym()]. +elf_symbols(#elf{symbols=Symbols}) -> Symbols. + +%%------------------------------------------------------------------------------ +%% Functions to manipulate String Table +%%------------------------------------------------------------------------------ + +%% ADT: get_strtab_entry/1 must be used to consume this type. +-type strtab() :: binary(). + +%% @doc Extracts String Table from an ELF formated Object File. +-spec extract_strtab(elf()) -> strtab(). +extract_strtab(Elf) -> + parse_strtab(extract_segment_by_name(Elf, ?STRTAB)). + +-spec parse_strtab(binary()) -> strtab(). +parse_strtab(StrTabSectionBin) -> StrTabSectionBin. + +%% @doc Returns the name of the symbol at the given offset. +-spec get_strtab_entry(non_neg_integer(), strtab()) -> string(). +get_strtab_entry(Offset, StrTab) -> + <<_:Offset/binary, StrBin/binary>> = StrTab, + bin_get_string(StrBin). + +%% @doc Extracts a null-terminated string from a binary. +-spec bin_get_string(binary()) -> string(). +%% FIXME: No regard for encoding (just happens to work for ASCII and Latin-1) +bin_get_string(<<0, _/binary>>) -> []; +bin_get_string(<<Char, Rest/binary>>) -> [Char|bin_get_string(Rest)]. + +%%------------------------------------------------------------------------------ +%% Functions to manipulate Relocations +%%------------------------------------------------------------------------------ + +%% @doc Extract the Relocations segment for section `Name' (that is passed +%% as second argument) from an ELF formated Object file binary. +-spec extract_rela(elf(), name()) -> [elf_rel()]. + +-ifdef(BIT32). +extract_rela(Elf, Name) -> + SecData = extract_segment_by_name(Elf, Name), + [#elf_rel{offset=Offset, symbol=elf_symbol(?ELF_R_SYM(Info), Elf), + type=decode_reloc_type(?ELF_R_TYPE(Info)), + addend=read_implicit_addend(Offset, SecData)} + || <<Offset:?bits(?R_OFFSET_SIZE)/little, + Info:?bits(?R_INFO_SIZE)/little % 386 uses ".rel" + >> <= extract_segment_by_name(Elf, ?REL(Name))]. + +%% The only types HiPE knows how to patch +decode_reloc_type(1) -> '32'; +decode_reloc_type(2) -> 'pc32'. + +read_implicit_addend(Offset, Section) -> + %% All x86 relocation types uses 'word32' relocation fields; i.e. 32-bit LE. + <<_:Offset/binary, Addend:32/signed-little, _/binary>> = Section, + Addend. + +-else. %% BIT32 +extract_rela(Elf, Name) -> + [#elf_rel{offset=Offset, symbol=elf_symbol(?ELF_R_SYM(Info), Elf), + type=decode_reloc_type(?ELF_R_TYPE(Info)), addend=Addend} + || <<Offset:?bits(?R_OFFSET_SIZE)/little, + Info:?bits(?R_INFO_SIZE)/little, + Addend:?bits(?R_ADDEND_SIZE)/signed-little % X86_64 uses ".rela" + >> <= extract_segment_by_name(Elf, ?RELA(Name))]. + +decode_reloc_type(1) -> '64'; +decode_reloc_type(2) -> 'pc32'; +decode_reloc_type(10) -> '32'. +-endif. %% BIT32 + +%%------------------------------------------------------------------------------ +%% Functions to manipulate Executable Code segment +%%------------------------------------------------------------------------------ + +%% @doc This function gets as arguments an ELF formated binary file and +%% returns the Executable Code (".text" segment) or an empty binary if it +%% is not found. +-spec extract_text(elf()) -> binary(). +extract_text(Elf) -> + extract_segment_by_name(Elf, ?TEXT). + +%%------------------------------------------------------------------------------ +%% Functions to manipulate Note Section +%%------------------------------------------------------------------------------ + +%% @doc Extract specific Note Section from an ELF Object file. The function +%% takes as first argument the object file (`Elf') and the `Name' of the +%% wanted Note Section (<b>without</b> the ".note" prefix!). It returns +%% the specified binary segment or an empty binary if no such section +%% exists. +-spec extract_note(elf(), string()) -> binary(). +extract_note(Elf, Name) -> + extract_segment_by_name(Elf, ?NOTE(Name)). + +%%------------------------------------------------------------------------------ +%% Functions to manipulate GCC Exception Table segment +%%------------------------------------------------------------------------------ + +%% A description for the C++ exception table formats can be found at Exception +%% Handling Tables (http://www.codesourcery.com/cxx-abi/exceptions.pdf). + +%% A list with `{Start, End, HandlerOffset}' for all call sites in the code +-spec get_exn_handlers(elf()) -> [{start(), start(), lp()}]. +get_exn_handlers(Elf) -> + CallSites = extract_gccexntab_callsites(Elf), + [{Start, Start + Size, LP} + || #elf_gccexntab_callsite{start = Start, size = Size, lp = LP} <- CallSites]. + +%% @doc This function gets as argument an ELF binary file and returns +%% the table (list) of call sites which is stored in GCC +%% Exception Table (".gcc_except_table") section. +%% It returns an empty list if the Exception Table is not found. +%% XXX: Assumes there is *no* Action Record Table. +extract_gccexntab_callsites(Elf) -> + case extract_segment_by_name(Elf, ?GCC_EXN_TAB) of + <<>> -> + []; + ExnTab -> + %% First byte of LSDA is Landing Pad base encoding. + <<LBenc:8, More/binary>> = ExnTab, + %% Second byte is the Landing Pad base (if its encoding is not + %% DW_EH_PE_omit) (optional). + {_LPBase, LSDACont} = + case LBenc =:= ?DW_EH_PE_omit of + true -> % No landing pad base byte. (-1 denotes that) + {-1, More}; + false -> % Landing pad base. + <<Base:8, More2/binary>> = More, + {Base, More2} + end, + %% Next byte of LSDA is the encoding of the Type Table. + <<TTenc:8, More3/binary>> = LSDACont, + %% Next byte is the Types Table offset encoded in U-LEB128 (optional). + {_TTOff, LSDACont2} = + case TTenc =:= ?DW_EH_PE_omit of + true -> % There is no Types Table pointer. (-1 denotes that) + {-1, More3}; + false -> % The byte offset from this field to the start of the Types + % Table used for exception matching. + leb128_decode(More3) + end, + %% Next byte of LSDA is the encoding of the fields in the Call-site Table. + <<_CSenc:8, More4/binary>> = LSDACont2, + %% Sixth byte is the size (in bytes) of the Call-site Table encoded in + %% U-LEB128. + {_CSTabSize, CSTab} = leb128_decode(More4), + %% Extract all call site information + get_gccexntab_callsites(CSTab, []) + end. + +get_gccexntab_callsites(<<>>, Acc) -> + lists:reverse(Acc); +get_gccexntab_callsites(CSTab, Acc) -> + %% We are only interested in the Landing Pad of every entry. + <<Start:32/integer-little, Size:32/integer-little, + LP:32/integer-little, OnAction:8, More/binary + >> = CSTab, + GccCS = mk_gccexntab_callsite(Start, Size, LP, OnAction), + get_gccexntab_callsites(More, [GccCS | Acc]). + +%%------------------------------------------------------------------------------ +%% Helper functions +%%------------------------------------------------------------------------------ + +%% @doc Returns the binary segment starting at `Offset' with length `Size' +%% (bytes) from a binary file. If `Offset' is bigger than the byte size of +%% the binary, an empty binary (`<<>>') is returned. +-spec get_binary_segment(binary(), offset(), size()) -> binary(). +get_binary_segment(Bin, Offset, _Size) when Offset > byte_size(Bin) -> + <<>>; +get_binary_segment(Bin, Offset, Size) -> + <<_Hdr:Offset/binary, BinSeg:Size/binary, _More/binary>> = Bin, + BinSeg. + +%% @doc This function gets as arguments an ELF formated binary object and +%% a string with the segments' name and returns the specified segment or +%% an empty binary (`<<>>') if there exists no segment with that name. +%% There are handy macros defined in elf_format.hrl for all Standard +%% Section Names. +-spec extract_segment_by_name(elf(), string()) -> binary(). +extract_segment_by_name(#elf{file=ElfBin, sec_nam=SecNam}, SectionName) -> + %% Find Section Header Table entry by name + case SecNam of + #{SectionName := #elf_shdr{offset=Offset, size=Size}} -> + get_binary_segment(ElfBin, Offset, Size); + #{} -> %% Not found. + <<>> + end. + +%% @doc Little-Endian Base 128 (LEB128) Decoder +%% This function extracts the <b>first</b> LEB128-encoded integer in a +%% binary and returns that integer along with the remaining binary. This is +%% done because a LEB128 number has variable bit-size and that is a way of +%% extracting only one number in a binary and continuing parsing the binary +%% for other kind of data (e.g. different encoding). +%% FIXME: Only decodes unsigned data! +-spec leb128_decode(binary()) -> {integer(), binary()}. +leb128_decode(LebNum) -> + leb128_decode(LebNum, 0, <<>>). + +-spec leb128_decode(binary(), integer(), binary()) -> {integer(), binary()}. +leb128_decode(LebNum, NoOfBits, Acc) -> + <<Sentinel:1/bits, NextBundle:7/bits, MoreLebNums/bits>> = LebNum, + case Sentinel of + <<1:1>> -> % more bytes to follow + leb128_decode(MoreLebNums, NoOfBits+7, <<NextBundle:7/bits, Acc/bits>>); + <<0:1>> -> % byte bundle stop + Size = NoOfBits+7, + <<Num:Size/integer>> = <<NextBundle:7/bits, Acc/bits>>, + {Num, MoreLebNums} + end. |