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394d998315
At least in neovim, `│vi:` is not recognized as a modeline because it has no preceding whitespace. After fixing this, opening a file yields an error because `net` is not an option. (`noet`, however, is.)
79 lines
4 KiB
C
79 lines
4 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│ vi: set noet ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi │
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2023 Justine Alexandra Roberts Tunney │
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│ │
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│ Permission to use, copy, modify, and/or distribute this software for │
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│ any purpose with or without fee is hereby granted, provided that the │
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│ above copyright notice and this permission notice appear in all copies. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
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│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
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│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
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│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
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│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
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│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
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│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
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│ PERFORMANCE OF THIS SOFTWARE. │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/elf/def.h"
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#include "libc/elf/elf.h"
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#include "libc/elf/scalar.h"
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#include "libc/elf/struct/ehdr.h"
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#include "libc/elf/struct/shdr.h"
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#include "libc/elf/struct/sym.h"
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/**
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* Returns pointer to the elf section header for a symbol table.
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*
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* The easiest way to get the symbol table is:
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*
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* Elf64_Xword i, n;
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* Elf64_Sym *st = GetElfSymbols(map, size, SHT_SYMTAB, &n);
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* for (i = 0; st && i < n; ++i) {
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* // st[i] holds a symbol
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* }
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*
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* This API is more verbose than the GetElfSymbols() shortcut, however
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* calling this the long way makes tricks like the following possible:
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*
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* Elf64_Xword i, n;
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* Elf64_Shdr *sh = GetElfSymbolTable(map, size, SHT_SYMTAB, &n);
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* Elf64_Sym *st = GetElfSectionAddress(map, size, sh);
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* if (st) {
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* for (i = sh->sh_info; i < n; ++i) {
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* // st[i] holds a non-local symbol
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* }
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* }
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*
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* Our code here only cares about `STB_GLOBAL` and `STB_WEAK` symbols
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* however `SHT_SYMTAB` usually has countless `STB_LOCAL` entries too
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* that must be skipped over. The trick is that the ELF spec requires
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* local symbols be ordered before global symbols, and that the index
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* dividing the two be stored to `sh_info`. So, if we start iterating
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* there, then we've cleverly avoided possibly dozens of page faults!
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*
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* @param elf points to the start of the executable image data
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* @param mapsize is the number of bytes past `elf` we can access
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* @param section_type is usually `SHT_SYMTAB` or `SHT_DYNSYM`
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* @param out_count optionally receives number of symbols
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* @return pointer to symbol table section header, otherwise null
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*/
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Elf64_Shdr *GetElfSymbolTable(const Elf64_Ehdr *elf, //
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size_t mapsize, //
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int section_type, //
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Elf64_Xword *out_count) {
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int i;
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Elf64_Shdr *shdr;
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for (i = elf->e_shnum; i > 0; --i) {
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if ((shdr = GetElfSectionHeaderAddress(elf, mapsize, i - 1)) && //
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shdr->sh_entsize == sizeof(Elf64_Sym) && //
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shdr->sh_type == section_type) {
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if (out_count) {
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*out_count = shdr->sh_size / sizeof(Elf64_Sym);
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}
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return shdr;
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}
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}
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return 0;
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}
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