Can't see my assembly source code with GDB

Question

I am starting to program linux x86_64 assembly code, and thus I was trying to debug just like one would normal C code, for examble when I run gdb -tui ./a.out, I get my source code and I can then toggle the registers to see what's going on, and go step by step, etc.

However that is not the case when I use it with assembly binaries, I simply get [ No Source Available ]. However I can see the registers and the resulting assembly code (given I do layout next). The thing is, since I am using C functions in the middle of my code (mainly printf, in order to simplify the IO process, as instructed by my professor); I would like to see my original assembly code. At the moment I have installed:

• gcc :(GCC) 12.2.0

• ld :GNU ld (GNU Binutils) 2.39.0

• NASM version 2.15.05

And to compile and run a program I run:

nasm -f elf64 -o hello.o hello.asm
gcc hello.o -o hello -no-pie 
gdb ./hello

Those were the commands that my teacher told us to run. I have read online that I could pass the -g flag to gcc to debug my code; it compiles just fine, but I can't see my source code either. I have also tried passing -g to nasm (same issue, compiles but no source code)

Is there a flag/setting that I'm not passing?

Answer 1

Just tell NASM to compile the source code with -g to add debugging symbols:

nasm -g -f elf64 -o hello.o hello.asm
gcc -m64 hello.o -o hello -no-pie
gdb hello

Once GDB opens, you can display the source code with list:

Reading symbols from hello...
(gdb) list
1           extern  printf          ; the C function, to be called
2   
3           section .data           ; Data section, initialized variables
4   msg:    db "Hello world", 0     ; C string needs 0
5   fmt:    db "%s", 10, 0          ; The printf format, "\n",'0'
6   
7           section .text           ; Code section.
8   
9           global main             ; the standard gcc entry point
10  main:                           ; the program label for the entry point

Here is a sample source code:

; Declare needed C  functions
        extern  printf          ; the C function, to be called

        section .data           ; Data section, initialized variables
msg:    db "Hello world", 0     ; C string needs 0
fmt:    db "%s", 10, 0          ; The printf format, "\n",'0'

        section .text           ; Code section.

        global main             ; the standard gcc entry point
main:                           ; the program label for the entry point
        push    rbp             ; set up stack frame, must be aligned
    
        mov rdi,fmt
        mov rsi,msg
        mov rax,0               ; or can be  xor  rax,rax
        call    printf          ; Call C function

        pop     rbp             ; restore stack 

        mov rax,0               ; normal, no error, return value
        ret                     ; return