Linux (64-bit), nasm and gdb

Question

I was searching other threads without luck. My problem is perhaps simple but frustrating. I'm compiling two files on 64-bit Ubuntu 11.04:

1. nasm -f elf64 -g file64.asm
2. gcc -g -o file file.c file64.o

Then I debug the resulting executables with gdb. With C, everything is OK. However, when debugging assembly, the source code is "not visible" to the debugger. I'm getting the following output:

(gdb) step
Single stepping until exit from function line,
which has no line number information.
0x0000000000400962 in convert ()

A quick investigation with:

objdump --source file64.o

shows that the assembly source code (and line information) is contained in the file.

Why can't I see it in a debug session? What am I doing wrong? These problems arose after moving to 64-bit Ubuntu. In the 32-bit Linux it worked (as it should).

Answer 1

With NASM, I've had much better experience in gdb when using the dwarf debugging format. gdb then treats the assembly source as if it were any other language (i.e., no disassemble commands necessary)

nasm -f elf64 -g -F dwarf file64.asm

(Versions 2.03.01 and later automatically enable -g if -F is specified.)

I'm using NASM version 2.10.07. I'm not sure if that makes a difference or not.