mirror of
https://github.com/jart/cosmopolitan.git
synced 2025-01-31 19:43:32 +00:00
0c630d95b5
The build/bootstrap/ar.com program is now tinier. This change reduces its size from 140kb to 53kb. Nothing was traded away. Cosmopolitan Ar performance is now 2x better than llvm-ar largely thanks to using the copy_file_range() system call. This change homebrews a new allocation API that addresses the shortcomings of the C standard library design. Using these new balloc() and reballoc() functions I managed to reduce memory consumption so much that Cosmpolitan Ar should now use roughly 100x fewer bytes of peak resident memory compared to llvm-ar. Correct behavior with better compatibility has been assured. Binary output is now pretty much bit-identical to llvm-ar, as of this change. This can and should be the living proof we need to show that a better world is possible for software.
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 -*-│
|
|
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
|
|
╞══════════════════════════════════════════════════════════════════════════════╡
|
|
│ Copyright 2023 Justine Alexandra Roberts Tunney │
|
|
│ │
|
|
│ Permission to use, copy, modify, and/or distribute this software for │
|
|
│ any purpose with or without fee is hereby granted, provided that the │
|
|
│ above copyright notice and this permission notice appear in all copies. │
|
|
│ │
|
|
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
|
|
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
|
|
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
|
|
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
|
|
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
|
|
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
|
|
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
|
|
│ PERFORMANCE OF THIS SOFTWARE. │
|
|
╚─────────────────────────────────────────────────────────────────────────────*/
|
|
#include "libc/elf/def.h"
|
|
#include "libc/elf/elf.h"
|
|
#include "libc/elf/scalar.h"
|
|
#include "libc/elf/struct/ehdr.h"
|
|
#include "libc/elf/struct/shdr.h"
|
|
#include "libc/elf/struct/sym.h"
|
|
|
|
/**
|
|
* Returns pointer to the elf section header for a symbol table.
|
|
*
|
|
* The easiest way to get the symbol table is:
|
|
*
|
|
* Elf64_Xword i, n;
|
|
* Elf64_Sym *st = GetElfSymbols(map, size, SHT_SYMTAB, &n);
|
|
* for (i = 0; st && i < n; ++i) {
|
|
* // st[i] holds a symbol
|
|
* }
|
|
*
|
|
* This API is more verbose than the GetElfSymbols() shortcut, however
|
|
* calling this the long way makes tricks like the following possible:
|
|
*
|
|
* Elf64_Xword i, n;
|
|
* Elf64_Shdr *sh = GetElfSymbolTable(map, size, SHT_SYMTAB, &n);
|
|
* Elf64_Sym *st = GetElfSectionAddress(map, size, sh);
|
|
* if (st) {
|
|
* for (i = sh->sh_info; i < n; ++i) {
|
|
* // st[i] holds a non-local symbol
|
|
* }
|
|
* }
|
|
*
|
|
* Our code here only cares about `STB_GLOBAL` and `STB_WEAK` symbols
|
|
* however `SHT_SYMTAB` usually has countless `STB_LOCAL` entries too
|
|
* that must be skipped over. The trick is that the ELF spec requires
|
|
* local symbols be ordered before global symbols, and that the index
|
|
* dividing the two be stored to `sh_info`. So, if we start iterating
|
|
* there, then we've cleverly avoided possibly dozens of page faults!
|
|
*
|
|
* @param elf points to the start of the executable image data
|
|
* @param mapsize is the number of bytes past `elf` we can access
|
|
* @param section_type is usually `SHT_SYMTAB` or `SHT_DYNSYM`
|
|
* @param out_count optionally receives number of symbols
|
|
* @return pointer to symbol table section header, otherwise null
|
|
*/
|
|
Elf64_Shdr *GetElfSymbolTable(const Elf64_Ehdr *elf, //
|
|
size_t mapsize, //
|
|
int section_type, //
|
|
Elf64_Xword *out_count) {
|
|
int i;
|
|
Elf64_Shdr *shdr;
|
|
for (i = elf->e_shnum; i > 0; --i) {
|
|
if ((shdr = GetElfSectionHeaderAddress(elf, mapsize, i - 1)) && //
|
|
shdr->sh_entsize == sizeof(Elf64_Sym) && //
|
|
shdr->sh_type == section_type) {
|
|
if (out_count) {
|
|
*out_count = shdr->sh_size / sizeof(Elf64_Sym);
|
|
}
|
|
return shdr;
|
|
}
|
|
}
|
|
return 0;
|
|
}
|