Re: -g1 is broken

["H . J . Lu" <hjl at lucon dot org>]

On Thu, Feb 14, 2002 at 03:03:52PM -0800, Richard Henderson wrote:
> On Wed, Feb 13, 2002 at 04:51:26PM -0800, H . J . Lu wrote:
> > When I tried to debug libgcc_so.so, which is compiled with -g1, I
> > couldn't get anything debug info on Linux/x86 with DWARF2. On Linux/mips
> > with stabs, the function line numbers are all wrong.
> 
> Err, -g1 doesn't emit line numbers.

That is true for gcc 2.96.

> 
> What were you expecting, exactly?
> 
> 

# /usr/gcc-3.1/bin/gcc -g1 -gstabs+ -S unwind-dw2-fde-glibc.c -O2

I got

        .stabs  "_Unwind_Find_FDE:F(1,1)=*(1,2)=(1,2)",36,0,23,_Unwind_Find_FDE
        .stabs  "pc:p(1,1)",160,0,22,8
.globl _Unwind_Find_FDE 
        .type   _Unwind_Find_FDE,@function
_Unwind_Find_FDE:
        .stabn 68,0,16,.LM6-_Unwind_Find_FDE
	            ^^^
.LM6:

The number 16 is bogus.

# /usr/gcc-3.1/bin/gcc -gstabs+ -S unwind-dw2-fde-glibc.c -O2

gave me

        .stabs  "_Unwind_Find_FDE:F(1,1)=*(1,2)=(1,2)",36,0,23,_Unwind_Find_FDE
        .stabs  "pc:p(1,1)",160,0,22,8
.globl _Unwind_Find_FDE 
        .type   _Unwind_Find_FDE,@function
_Unwind_Find_FDE:
        .stabn 68,0,23,.LM10-_Unwind_Find_FDE
		    ^^
.LM10:

Line 23 is correct.

As for DWARF-2, it is even worse:

(gdb) set env LD_LIBRARY_PATH .:../i686-pc-linux-gnu/libstdc++-v3/src/.libs/
(gdb) r
Starting program: /export/build/gnu/gcc/build-i686-linux/gcc/a.out 

Program exited with code 0143.
Current language:  auto; currently c
(gdb) b main
Breakpoint 1 at 0x80486a0: file /home/hjl/tmp/foo.cc, line 4.
(gdb) r
Starting program: /export/build/gnu/gcc/build-i686-linux/gcc/a.out 

Breakpoint 1, main () at /home/hjl/tmp/foo.cc:4
4         int n = 0;
Current language:  auto; currently c++
(gdb) b _Unwind_Find_FDE
Breakpoint 2 at 0x400ffe96
(gdb) c
Continuing.

Breakpoint 2, 0x400ffe96 in _Unwind_Find_FDE () from ./libgcc_s.so.1
Current language:  auto; currently c
(gdb) bt
#0  0x400ffe96 in _Unwind_Find_FDE () from ./libgcc_s.so.1
#1  0x400fdc15 in uw_frame_state_for () from ./libgcc_s.so.1
#2  0x400fe180 in uw_init_context_1 () from ./libgcc_s.so.1
#3  0x400fe3f8 in _Unwind_RaiseException () from ./libgcc_s.so.1
#4  0x400a57b9 in __cxa_throw (obj=0x804a908, tinfo=0xbffff664, 
    dest=0xbffff664)
    at
/home/hjl/work/gnu/src/gcc-mips/gcc/libstdc++-v3/libsupc++/eh_throw.cc:72
#5  0x080486d1 in main () at /home/hjl/tmp/foo.cc:8
#6  0x4011b3e7 in __libc_start_main (main=0x8048690 <main>, argc=1, 
    ubp_av=0xbffff754, init=0x8048530 <_init>, fini=0x8048740 <_fini>, 
    rtld_fini=0x4000d5f4 <_dl_fini>, stack_end=0xbffff74c)
    at ../sysdeps/generic/libc-start.c:129

I didn't even get function prototype.


H.J.
--unwind-dw2-fde-glibc.c---
static unsigned int
size_of_encoded_value (unsigned char encoding)
{
  if (encoding == 0xff)
    return 0;

  switch (encoding & 0x07)
    {
    case 0x00:
      return sizeof (void *);
    case 0x02:
      return 2;
    case 0x03:
      return 4;
    case 0x04:
      return 8;
    }
  abort ();
}

void *
_Unwind_Find_FDE (void *pc)
{
  return 0;
}