fusl/src/internal/vdso.c

#include <elf.h>
#include <limits.h>
#include <stdint.h>
#include <string.h>
#include "libc.h"
#include "syscall.h"

#ifdef VDSO_USEFUL

#if ULONG_MAX == 0xffffffff
typedef Elf32_Ehdr Ehdr;
typedef Elf32_Phdr Phdr;
typedef Elf32_Sym Sym;
typedef Elf32_Verdef Verdef;
typedef Elf32_Verdaux Verdaux;
#else
typedef Elf64_Ehdr Ehdr;
typedef Elf64_Phdr Phdr;
typedef Elf64_Sym Sym;
typedef Elf64_Verdef Verdef;
typedef Elf64_Verdaux Verdaux;
#endif

static int checkver(Verdef* def, int vsym, const char* vername, char* strings) {
  vsym &= 0x7fff;
  for (;;) {
    if (!(def->vd_flags & VER_FLG_BASE) && (def->vd_ndx & 0x7fff) == vsym)
      break;
    if (def->vd_next == 0)
      return 0;
    def = (Verdef*)((char*)def + def->vd_next);
  }
  Verdaux* aux = (Verdaux*)((char*)def + def->vd_aux);
  return !strcmp(vername, strings + aux->vda_name);
}

#define OK_TYPES \
  (1 << STT_NOTYPE | 1 << STT_OBJECT | 1 << STT_FUNC | 1 << STT_COMMON)
#define OK_BINDS (1 << STB_GLOBAL | 1 << STB_WEAK | 1 << STB_GNU_UNIQUE)

void* __vdsosym(const char* vername, const char* name) {
  size_t i;
  for (i = 0; libc.auxv[i] != AT_SYSINFO_EHDR; i += 2)
    if (!libc.auxv[i])
      return 0;
  Ehdr* eh = (void*)libc.auxv[i + 1];
  Phdr* ph = (void*)((char*)eh + eh->e_phoff);
  size_t *dynv = 0, base = -1;
  for (i = 0; i < eh->e_phnum; i++, ph = (void*)((char*)ph + eh->e_phentsize)) {
    if (ph->p_type == PT_LOAD)
      base = (size_t)eh + ph->p_offset - ph->p_vaddr;
    else if (ph->p_type == PT_DYNAMIC)
      dynv = (void*)((char*)eh + ph->p_offset);
  }
  if (!dynv || base == (size_t)-1)
    return 0;

  char* strings = 0;
  Sym* syms = 0;
  uint32_t* hashtab = 0;
  uint16_t* versym = 0;
  Verdef* verdef = 0;

  for (i = 0; dynv[i]; i += 2) {
    void* p = (void*)(base + dynv[i + 1]);
    switch (dynv[i]) {
      case DT_STRTAB:
        strings = p;
        break;
      case DT_SYMTAB:
        syms = p;
        break;
      case DT_HASH:
        hashtab = p;
        break;
      case DT_VERSYM:
        versym = p;
        break;
      case DT_VERDEF:
        verdef = p;
        break;
    }
  }

  if (!strings || !syms || !hashtab)
    return 0;
  if (!verdef)
    versym = 0;

  for (i = 0; i < hashtab[1]; i++) {
    if (!(1 << (syms[i].st_info & 0xf) & OK_TYPES))
      continue;
    if (!(1 << (syms[i].st_info >> 4) & OK_BINDS))
      continue;
    if (!syms[i].st_shndx)
      continue;
    if (strcmp(name, strings + syms[i].st_name))
      continue;
    if (versym && !checkver(verdef, versym[i], vername, strings))
      continue;
    return (void*)(base + syms[i].st_value);
  }

  return 0;
}

#endif