Using GDB to debug a program assembled with NASM

From: Joshua Davies (spamtrap_at_crayne.org)
Date: 11/01/04 

Date: Mon, 1 Nov 2004 21:56:39 +0000 (UTC)

Hi, I'm new to assembler programming - NASM seems to be a natural
choice for assembler programming under Linux, but I'm having trouble
getting GDB to debug my apps. If I have the following file named
sample.asm:

  section .text
    global _start

  _start:
    mov eax, 1
    add eax, 5

    mov ebx, 0 ; return code
    mov eax, 1 ; syscall 'exit'
    int 0x80

and assemble it with:

$ nasm -f elf -g sample.asm
$ ld sample.o

I can run the resulting a.out just fine. I'd like to step through it
with a debugger, but when I load it with gdb, it won't let me
single-step:

$ gdb a.out
(gdb) break _start
Breakpoint 1 at 0x8048080: file sample.asm, line 6.
(gdb) set step-mode on
(gdb) r
Starting program: a.out

Program exited normally.
(gdb)

It seems to set the breakpoint (I don't get an error message), but it
doesn't stop - it just runs through the whole program. I've tried it
with step-mode on & off (the default) with no luck. Can anybody see
what I'm missing?

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