github.com/afumu/libc@v0.0.6/musl/src/internal/vdso.c (about)

     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