elf.c

#include <elf.h>
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>

Elf32_Ehdr Elf_Header;
Elf32_Shdr Section_Header;

/**
 * Load the ELF header.
 * Returns zero on failure, or number of bytes read.
 */
size_t load_elf_header(FILE *fp);

/**
 * Read Nth section header.
 * Returns zero on failure, or number of bytes read.
 */
size_t load_section_header(FILE *fp, uint16_t n);

/**
 * Returns a copy of section header string table.
 * Returns NULL on failure
 */
char *shstrtab(FILE *fp);

void dump_shstrtab(FILE *fp);

int main(int argc, char *argv[]) {
  FILE *fp;

  if (argc != 2) {
    fprintf(stderr, "usage: %s <path>\n", argv[0]);
    return -1;
  }

  fp = fopen(argv[1], "r");
  if (fp == NULL) {
    perror("fopen");
    return -1;
  }

  if (!load_elf_header(fp)) {
    perror("load_elf_header");
    fclose(fp);
    return -1;
  }

  dump_shstrtab(fp);

  return 0;
}

size_t load_elf_header(FILE *fp) {
  rewind(fp); // TODO: ftell?
  return fread(&Elf_Header, sizeof(Elf32_Ehdr), 1, fp);
}

size_t load_section_header(FILE *fp, uint16_t n) {
  Elf32_Off offset = Elf_Header.e_shoff + n * sizeof(Elf32_Shdr);
  if (fseek(fp, offset, SEEK_SET) < 0) {
    return 0;
  }
  return fread(&Section_Header, sizeof(Elf32_Shdr), 1, fp);
}

char *shstrtab(FILE *fp) {
  if (!load_section_header(fp, Elf_Header.e_shstrndx)) {
    return NULL;
  }
  if (fseek(fp, Section_Header.sh_offset, SEEK_SET) < 0) {
    return NULL;
  }
  char *s = malloc(Section_Header.sh_size);
  if (s) {
    if (!fread(s, Section_Header.sh_size, 1, fp)) {
      free(s);
      return NULL;
    }
  }
  return s;
}

void dump_shstrtab(FILE *fp) {
  char *strtab = shstrtab(fp);
  if (!strtab) {
    perror("shstrtab");
    return;
  }

  uint16_t i;
  for (i = 0; i < Elf_Header.e_shnum; i++) {
    if (!load_section_header(fp, i)) {
      perror("load_section_header");
      free(strtab);
      return;
    }
    char *name = strtab + Section_Header.sh_name;
    printf("section %d: %s\n", i, name);
  }
  free(strtab);
}