commands/swifi/read_nlist.c

   1 /* ELF functions-only symbol table extractor by David van Moolenbroek.
   2  * Replaces generic a.out version by Philip Homburg.
   3  * Temporary solution until libc's nlist(3) becomes usable.
   4  */
   5 #include <stdlib.h>
   6 #include <stdio.h>
   7 #include <string.h>
   8 #include <unistd.h>
   9 #include <fcntl.h>
  10 #include <errno.h>
  11 #include <libelf.h>
  12 #include <nlist.h>
  13
  14 static int get_syms(Elf *elf, Elf_Scn *scn, Elf32_Shdr *shdr,
  15         struct nlist **nlistp)
  16 {
  17         Elf_Data *data;
  18         Elf32_Sym *sym;
  19         unsigned long nsyms;
  20         struct nlist *nlp;
  21         char *name;
  22         size_t size;
  23         int i;
  24
  25         if ((data = elf_getdata(scn, NULL)) == NULL) {
  26                 errno = ENOEXEC;
  27                 return -1;
  28         }
  29
  30         nsyms = data->d_size / sizeof(Elf32_Sym);
  31
  32         size = sizeof(struct nlist) * nsyms;
  33         if ((*nlistp = nlp = malloc(size)) == NULL)
  34                 return -1;
  35         memset(nlp, 0, size);
  36
  37         sym = (Elf32_Sym *) data->d_buf;
  38         for (i = 0; i < nsyms; i++, sym++, nlp++) {
  39                 nlp->n_value = sym->st_value;
  40
  41                 /* The caller only cares about N_TEXT. Properly setting other
  42                  * types would involve crosschecking with section types.
  43                  */
  44                 switch (ELF32_ST_TYPE(sym->st_info)) {
  45                 case STT_FUNC:   nlp->n_type = N_TEXT; break;
  46                 default:         nlp->n_type = N_UNDF; break;
  47                 }
  48
  49                 name = elf_strptr(elf, shdr->sh_link, (size_t) sym->st_name);
  50                 if ((nlp->n_name = strdup(name ? name : "")) == NULL) {
  51                         free(*nlistp);
  52                         return -1;
  53                 }
  54         }
  55
  56         return nsyms;
  57 }
  58
  59 int read_nlist(const char *filename, struct nlist **nlist_table)
  60 {
  61         /* Read in the symbol table of 'filename'. Return the resulting symbols
  62          * as an array, with 'nlist_table' set to point to it, and the number
  63          * of elements as the return value. The caller has no way to free the
  64          * results. Return 0 if the executable contains no symbols. Upon error,
  65          * return -1 and set errno to an appropriate value.
  66          */
  67         Elf *elf;
  68         Elf_Scn *scn;
  69         Elf32_Shdr *shdr;
  70         int res, fd;
  71
  72         if (elf_version(EV_CURRENT) == EV_NONE) {
  73                 errno = EINVAL;
  74                 return -1;
  75         }
  76
  77         if ((fd = open(filename, O_RDONLY)) < 0)
  78                 return -1;
  79
  80         elf = elf_begin(fd, ELF_C_READ, NULL);
  81         if (elf == NULL) {
  82                 errno = ENOEXEC;
  83                 close(fd);
  84                 return -1;
  85         }
  86
  87         scn = NULL;
  88         res = 0;
  89         while ((scn = elf_nextscn(elf, scn)) != NULL) {
  90                 if ((shdr = elf32_getshdr(scn)) == NULL)
  91                         continue;
  92
  93                 if (shdr->sh_type != SHT_SYMTAB)
  94                         continue;
  95
  96                 res = get_syms(elf, scn, shdr, nlist_table);
  97                 break;
  98         }
  99
 100         elf_end(elf);
 101         close(fd);
 102
 103         return res;
 104 }