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https://github.com/JuliaLang/julia.git
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ac4ee59e16
Somewhat of a companion to https://github.com/JuliaLang/julia/pull/60248. For a small application that has just started up `fork()` is not a huge concern, but it's quite heavy-handed for Julia- as-a-library scenarios where resident memory may already be large. Many soft-embedded targets also do not support fork() well, so it is good for our compatibility to adjust this. Rather than relying on the linker to do all of the heavy lifting, this changes our `libstdcxx` probe sequence to directly parse the `ld.so.cache` and `libstdc++.so.6` files. As long as we can expect `/etc/ld.so.cache` to be the same path on all Linux systems, this seems to be a reliable way to locate system libraries.
124 lines
3.5 KiB
C
124 lines
3.5 KiB
C
#include "../src/support/platform.h"
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#include "loader.h"
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#ifdef _OS_LINUX_
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#include <stdio.h>
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#include <assert.h>
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#include <stddef.h>
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#include <stdint.h>
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#include <string.h>
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#include <sys/mman.h>
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#include <linux/elf.h>
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static Elf64_Shdr *Elf64_get_section(Elf64_Ehdr *hdr, size_t i)
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{
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size_t section_header_sz = hdr->e_shentsize;
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size_t byte_offset = hdr->e_shoff + i * section_header_sz;
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return (Elf64_Shdr *)&((char *)hdr)[byte_offset];
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}
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static const char *Elf64_get_strtab(Elf64_Ehdr *hdr, Elf64_Shdr *section)
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{
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return &((const char *)hdr)[section->sh_offset];
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}
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static Elf64_Sym *Elf64_get_symbol(Elf64_Ehdr *hdr, Elf64_Shdr *section, size_t i)
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{
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size_t byte_offset = section->sh_offset + i * section->sh_entsize;
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return (Elf64_Sym *)&((char *)hdr)[byte_offset];
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}
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static int Elf64_locate_symbol(Elf64_Ehdr *hdr, const char *symbol)
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{
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if (hdr->e_type != ET_DYN)
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return 0;
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for (size_t sect_idx = 0; sect_idx < hdr->e_shnum; sect_idx++) {
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Elf64_Shdr *shdr = Elf64_get_section(hdr, sect_idx);
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if (shdr->sh_type != SHT_DYNSYM)
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continue;
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Elf64_Shdr *strtab_shdr = Elf64_get_section(hdr, shdr->sh_link);
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const char *strtab = Elf64_get_strtab(hdr, strtab_shdr);
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size_t nsymbols = shdr->sh_size / shdr->sh_entsize;
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for (size_t i = 0; i < nsymbols; i++) {
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Elf64_Sym *sym = Elf64_get_symbol(hdr, shdr, i);
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const char *name = &strtab[sym->st_name];
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if (strcmp(name, symbol) == 0)
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return 1;
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}
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}
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return 0;
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}
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static Elf32_Shdr *Elf32_get_section(Elf32_Ehdr *hdr, size_t i)
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{
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size_t section_header_sz = hdr->e_shentsize;
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size_t byte_offset = hdr->e_shoff + i * section_header_sz;
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return (Elf32_Shdr *)&((char *)hdr)[byte_offset];
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}
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static const char *Elf32_get_strtab(Elf32_Ehdr *hdr, Elf32_Shdr *section)
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{
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return &((const char *)hdr)[section->sh_offset];
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}
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static Elf32_Sym *Elf32_get_symbol(Elf32_Ehdr *hdr, Elf32_Shdr *section, size_t i)
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{
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size_t byte_offset = section->sh_offset + i * section->sh_entsize;
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return (Elf32_Sym *)&((char *)hdr)[byte_offset];
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}
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static int Elf32_locate_symbol(Elf32_Ehdr *hdr, const char *symbol)
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{
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if (hdr->e_type != ET_DYN)
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return 0;
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for (size_t sect_idx = 0; sect_idx < hdr->e_shnum; sect_idx++) {
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Elf32_Shdr *shdr = Elf32_get_section(hdr, sect_idx);
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if (shdr->sh_type != SHT_DYNSYM)
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continue;
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Elf32_Shdr *strtab_shdr = Elf32_get_section(hdr, shdr->sh_link);
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const char *strtab = Elf32_get_strtab(hdr, strtab_shdr);
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size_t nsymbols = shdr->sh_size / shdr->sh_entsize;
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for (size_t i = 0; i < nsymbols; i++) {
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Elf32_Sym *sym = Elf32_get_symbol(hdr, shdr, i);
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const char *name = &strtab[sym->st_name];
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if (strcmp(name, symbol) == 0)
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return 1;
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}
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}
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return 0;
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}
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int jl_loader_locate_symbol(const char *library, const char *symbol)
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{
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size_t library_sz;
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void *elf_file = jl_loader_open_via_mmap(library, &library_sz);
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if (elf_file == NULL)
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return 0;
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int found = 0;
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const char *hdr = (const char *)elf_file;
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if (strncmp(hdr, ELFMAG, SELFMAG) != 0)
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goto bail;
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assert(hdr[5] == ELFDATA2LSB);
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if (hdr[4] == ELFCLASS32) {
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found = Elf32_locate_symbol((Elf32_Ehdr *)hdr, symbol);
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} else if (hdr[4] == ELFCLASS64) {
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found = Elf64_locate_symbol((Elf64_Ehdr *)hdr, symbol);
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}
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bail:
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munmap(elf_file, library_sz);
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return found;
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}
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#endif
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