cassemblygccsegmentation-faultcrt

C to ASM increment causes Segfault


I have the following C program:

#include <stdio.h>

int main() {
    int i = 0;
    int N = 10;
    while(i < N) {
        printf("counting to %d: %d", N, i);
        //i = i + 1;
    }
    return 0;
}

I would like to compile this first to assembly, then to binary for instructional purposes. So, I issue the following commands:

$ gcc -S count.c -o count.s
$ as -o count.o count.s
$ ld -o count -e main -dynamic-linker /lib64/ld-linux-x86-64.so.2 /usr/lib/x86_64-linux-gnu/libc.so count.o -lc

These compile the C to assembly, assemble the assembly to binary, and then link the library containing the printf function, respectively.

This works. Output:

counting to 10: 0counting to 10: 0counting to 10: 0counting to 10: 0counting to 10: 0counting to 10: 0counting to 10: 0counting to 10: 0counting to 10: 0counting to 10: 0counting to 10: 0counting to 10: 0counting to 10: 0

etc until I ctrl-c the program.

However, when I uncomment the i = i + 1 line:

Segmentation fault (core dumped)

What is going wrong here?

UPDATE: Here is count.s (with the i = i + 1 line included)

    .file   "count.c"
    .text
    .section    .rodata
.LC0:
    .string "counting to %d: %d"
    .text
    .globl  main
    .type   main, @function
main:
.LFB0:
    .cfi_startproc
    pushq   %rbp
    .cfi_def_cfa_offset 16
    .cfi_offset 6, -16
    movq    %rsp, %rbp
    .cfi_def_cfa_register 6
    subq    $16, %rsp
    movl    $0, -8(%rbp)
    movl    $10, -4(%rbp)
    jmp .L2
.L3:
    movl    -8(%rbp), %edx
    movl    -4(%rbp), %eax
    movl    %eax, %esi
    leaq    .LC0(%rip), %rdi
    movl    $0, %eax
    call    printf@PLT
    addl    $1, -8(%rbp)
.L2:
    movl    -8(%rbp), %eax
    cmpl    -4(%rbp), %eax
    jl  .L3
    movl    $0, %eax
    leave
    .cfi_def_cfa 7, 8
    ret
    .cfi_endproc
.LFE0:
    .size   main, .-main
    .ident  "GCC: (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0"
    .section    .note.GNU-stack,"",@progbits

Solution

  • The below works perfectly fine for me on Ubuntu 20 (taken from Ciro Santilli's answer at Linking a C program directly with ld fails with undefined reference to `__libc_csu_fini`).

    gcc -S count.c -o count.s
    as -o count.o count.s
    ld -o count -dynamic-linker /lib64/ld-linux-x86-64.so.2 /usr/lib/x86_64-linux-gnu/crt1.o /usr/lib/x86_64-linux-gnu/crti.o -L/usr/lib/gcc/x86_64-linux-gnu/4.8/ -lc count.o /usr/lib/x86_64-linux-gnu/crtn.o