打印节标题的精灵名称

Question

I have a C program where I want to print out names of section headers of input file. I made everything based on researching ELF notation and helped with existing programs on internet but it still doesn't work. It printed only indexes from for loop where also should to be section names. Anyone see something I missed?

Update: I updated the code and remove the bug which causes Stack Overflow if anyone in future will need it.

Code:

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <elf.h>

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


    int fd;
    int val;

    Elf32_Ehdr elfHdr;
    Elf32_Shdr sectHdr;
    FILE* ElfFile = NULL;
    char* SectNames = NULL;

    if(argc != 2) {
        perror("Error while opening file");
        return 0;
    }   



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

    //preberemo elf header
    fread(&elfHdr, 1, sizeof(Elf32_Ehdr), ElfFile);

    printf("\tVersion: 0x%.2X\n", elfHdr.e_version);

    printf("\tEntry point address: 0x%.8X\n", elfHdr.e_entry);

    printf("\tProgram header offset: 0x%.8X\n", elfHdr.e_phoff);

    printf("\tSection header offset: 0x%.8X\n", elfHdr.e_shoff);

    printf("\tFlags: 0x%.8X\n", elfHdr.e_flags);

    printf("\tSize of this header: 0x%X\n", elfHdr.e_ehsize);

    printf("\tSize of program headers: 0x%X\n", elfHdr.e_phentsize);

    printf("\tNumber of program headers: %d\n", elfHdr.e_phnum);

    printf("\tSize of section headers: 0x%X\n", elfHdr.e_shentsize);

    printf("\tNumber of section headers: %d\n", elfHdr.e_shnum);

    printf("\tSection header string table index: 0x%X\n", elfHdr.e_shstrndx);

    //premik do section tabele
    fseek(ElfFile, elfHdr.e_shoff + elfHdr.e_shstrndx * elfHdr.e_shentsize, SEEK_SET);
    fread(&sectHdr, 1, sizeof(sectHdr), ElfFile);
    SectNames = malloc(sectHdr.sh_size);
    fseek(ElfFile, sectHdr.sh_offset, SEEK_SET);
    fread(SectNames, 1, sectHdr.sh_size, ElfFile);

    for (int idx = 0; idx < elfHdr.e_shnum; idx++){
        char* name = "";

        fseek(ElfFile, elfHdr.e_shoff + idx * sizeof(sectHdr), SEEK_SET);
        fread(&sectHdr, 1, sizeof(sectHdr), ElfFile);

        // print section name
        if (sectHdr.sh_name);
        name = SectNames + sectHdr.sh_name;
            
        printf("%i %s\n", idx, name);
    }



    close(fd);

    return 0;
}

Answer 1

Anyone see something I missed?

Did you compile your program in 32-bit mode?

Update:

There is an "obvious" bug, which I missed on first reading, and which was exposed by building with -fsanitize=address :

Elf32_Ehdr elfHdr;
...
fread(&elfHdr, 1, sizeof(Elf64_Ehdr), ElfFile);

This bug causes stack buffer overflow. To prevent such bugs, it is always safer to use sizeof(variable) instead of sizeof(Type) , eg

fread(&elfHdr, 1, sizeof(elfHdr), ElfFile);

It works for me:

gcc -w -m32 t.c && ./a.out ./a.out
    Version: 0x01
    Entry point address: 0x000010C0
    Program header offset: 0x00000034
    Section header offset: 0x000038B0
    Flags: 0x00000000
    Size of this header: 0x34
    Size of program headers: 0x20
    Number of program headers: 11
    Size of section headers: 0x28
    Number of section headers: 30
    Section header string table index: 0x1D
0
1 .interp
2 .note.gnu.build-id
3 .note.ABI-tag
4 .gnu.hash
5 .dynsym
6 .dynstr
7 .gnu.version
8 .gnu.version_r
9 .rel.dyn
10 .rel.plt
11 .init
12 .plt
13 .plt.got
14 .text
15 .fini
16 .rodata
17 .eh_frame_hdr
18 .eh_frame
19 .init_array
20 .fini_array
21 .dynamic
22 .got
23 .got.plt
24 .data
25 .bss
26 .comment
27 .symtab
28 .strtab
29 .shstrtab

If you are trying to run it on a 64-bit ELF file, then you need to change Elf32_Ehdr and Elf32_Shdr with their Elf64_... equivalents.