src/internal/vdso.c

   1 #include <elf.h>
   2 #include <link.h>
   3 #include <limits.h>
   4 #include <stdint.h>
   5 #include <string.h>
   6 #include "libc.h"
   7 #include "syscall.h"
   8
   9 #ifdef VDSO_USEFUL
  10
  11 #if ULONG_MAX == 0xffffffff
  12 typedef Elf32_Ehdr Ehdr;
  13 typedef Elf32_Phdr Phdr;
  14 typedef Elf32_Sym Sym;
  15 typedef Elf32_Verdef Verdef;
  16 typedef Elf32_Verdaux Verdaux;
  17 #else
  18 typedef Elf64_Ehdr Ehdr;
  19 typedef Elf64_Phdr Phdr;
  20 typedef Elf64_Sym Sym;
  21 typedef Elf64_Verdef Verdef;
  22 typedef Elf64_Verdaux Verdaux;
  23 #endif
  24
  25 static int checkver(Verdef *def, int vsym, const char *vername, char *strings)
  26 {
  27         vsym &= 0x7fff;
  28         for (;;) {
  29                 if (!(def->vd_flags & VER_FLG_BASE)
  30                   && (def->vd_ndx & 0x7fff) == vsym)
  31                         break;
  32                 if (def->vd_next == 0)
  33                         return 0;
  34                 def = (Verdef *)((char *)def + def->vd_next);
  35         }
  36         Verdaux *aux = (Verdaux *)((char *)def + def->vd_aux);
  37         return !strcmp(vername, strings + aux->vda_name);
  38 }
  39
  40 #define OK_TYPES (1<<STT_NOTYPE | 1<<STT_OBJECT | 1<<STT_FUNC | 1<<STT_COMMON)
  41 #define OK_BINDS (1<<STB_GLOBAL | 1<<STB_WEAK | 1<<STB_GNU_UNIQUE)
  42
  43 void *__vdsosym(const char *vername, const char *name)
  44 {
  45         size_t i;
  46         for (i=0; libc.auxv[i] != AT_SYSINFO_EHDR; i+=2)
  47                 if (!libc.auxv[i]) return 0;
  48         if (!libc.auxv[i+1]) return 0;
  49         Ehdr *eh = (void *)libc.auxv[i+1];
  50         Phdr *ph = (void *)((char *)eh + eh->e_phoff);
  51         size_t *dynv=0, base=-1;
  52         for (i=0; i<eh->e_phnum; i++, ph=(void *)((char *)ph+eh->e_phentsize)) {
  53                 if (ph->p_type == PT_LOAD)
  54                         base = (size_t)eh + ph->p_offset - ph->p_vaddr;
  55                 else if (ph->p_type == PT_DYNAMIC)
  56                         dynv = (void *)((char *)eh + ph->p_offset);
  57         }
  58         if (!dynv || base==(size_t)-1) return 0;
  59
  60         char *strings = 0;
  61         Sym *syms = 0;
  62         Elf_Symndx *hashtab = 0;
  63         uint16_t *versym = 0;
  64         Verdef *verdef = 0;
  65
  66         for (i=0; dynv[i]; i+=2) {
  67                 void *p = (void *)(base + dynv[i+1]);
  68                 switch(dynv[i]) {
  69                 case DT_STRTAB: strings = p; break;
  70                 case DT_SYMTAB: syms = p; break;
  71                 case DT_HASH: hashtab = p; break;
  72                 case DT_VERSYM: versym = p; break;
  73                 case DT_VERDEF: verdef = p; break;
  74                 }
  75         }
  76
  77         if (!strings || !syms || !hashtab) return 0;
  78         if (!verdef) versym = 0;
  79
  80         for (i=0; i<hashtab[1]; i++) {
  81                 if (!(1<<(syms[i].st_info&0xf) & OK_TYPES)) continue;
  82                 if (!(1<<(syms[i].st_info>>4) & OK_BINDS)) continue;
  83                 if (!syms[i].st_shndx) continue;
  84                 if (strcmp(name, strings+syms[i].st_name)) continue;
  85                 if (versym && !checkver(verdef, versym[i], vername, strings))
  86                         continue;
  87                 return (void *)(base + syms[i].st_value);
  88         }
  89
  90         return 0;
  91 }
  92
  93 #endif