Local labels in GNU assembler; gdb printing backtrace as though labels are functions

Question

Two pieces of example code; first some C++ code calling into assembly:

/* test1.cc */
#include <stdio.h>

extern "C" void blah();
extern "C" void stuff() {
  printf( "This is a test\n" );
}

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

  return 0;
}

... then the assembly:

.file "test2.s"
.text
.globl blah, stuff
.type blah,@function
.type stuff,@function
.align 16

blah:
  /* normal function preamble */
  pushl %ebp
  movl %esp, %ebp

label1:
  call stuff

  leave
  retn

Built with:

as -g --32 test2.s -o test2.o
clang++ -m32 -g test1.cc -c
clang++ -m32 -g test*.o -o test

Run it under gdb, set a breakpoint on stuff(), then look at the backtrace:

gdb test
(gdb) break stuff
(gdb) run
(gdb) back
     #0  stuff () at test1.cc:5
---> #1  0x08048458 in label1 () at test2.s:12
---> #2  0xffffc998 in ?? ()
     #3  0x0804843e in main (argc=1, argv=0xffffca44) at test1.cc:9

After sifting through [edit an older copy of] the GNU assembler documentation, I tried labels prefixed with L & postfixed with $ to see if it would prevent the labels from being exported, but it didn't work.

If I make the labels numeric the backtrace looks normal, but I'm not overly fond of the notion of using numeric labels.

Could someone point me in the right direction, please?

Chubby

Local labels should start with .L (dot L). For example, .Llabel1 works. – Sabol

Answer 1

I found an answer in the GNU assembler manual; quoting from that doc:

A local symbol is any symbol beginning with certain local label prefixes. By default, the local label prefix is ‘.L’ for ELF systems or ‘L’ for traditional a.out systems, but each target may have its own set of local label prefixes.

Sure enough, as soon as I put .L on there, it worked.

.L labels don't appear as symbols in the object file.

Chubby

I asked if there is any way to break on such local labels: #55227298 – Brookebrooker