vdso.c raw

   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
  94