CODEWITHSUNDEEP
celfobjdump
Laodis
Laodis

Reputation: 17

Get the full contents of any section of an ELF file in C code

I want to get the full contents of any sections in an ELF file,

I can get the name of the content with this code:

int fd;
int counter;
int filesize;
void *data;
char *strtab;
Elf64_Ehdr  *elf;
Elf64_Shdr  *shdr;

counter = 0;
fd = open(av[1], O_RDONLY);
if (fd == -1) {
    perror("open : ");
    return (84);
}
filesize = lseek(fd, 0, SEEK_END);
data = mmap(NULL, filesize, PROT_READ, MAP_SHARED, fd, 0);
if (data != NULL) {
    elf = (Elf64_Ehdr *)(data);
    shdr = (Elf64_Shdr *)(data + elf->e_shoff);
    strtab = (char *)(data + shdr[elf->e_shstrndx].sh_offset);
    while(counter < elf->e_shnum) {
        printf("Contents of section %s:\n", &strtab[shdr[counter].sh_name]);
        counter ++;
    }
    return (EXIT_SUCCESS);
}
perror("mmap : ");
return (EXIT_FAILURE);

I found that the shdr structure contain many pieces of information but I want the information given by the objdump -s a.out command and I can’t find the structure that gives all the information.

Can you help me to find a lead or a name of a structure where I can find this information, please?

Upvotes: 0

Views: 1015

Answers (1)

Employed Russian
Employed Russian

Reputation: 213385

This is a bug:

if (data != NULL) {

because mmap doesn't return NULL on failure (it returns MAP_FAILED).

Your shdr variable points to struct Elf64_Shdr, which has .sh_offset and .sh_size fields. To get the contents of the section, you want to dump .sh_size bytes located at (char *)data + shdr->sh_offset.

Upvotes: 1

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