[Qemu-devel] setting MIPS gdb breakpoints have wrong offsets

[Qemu-devel] setting MIPS gdb breakpoints have wrong offsets

[Dirk Behme]

Hi,

I just tried to debug some simple MIPS code using 
qemu-system-mipsel by setting some breakpoints. If I use 
gdb's break command with symbol names the breakpoints are 
set at offsets and therefore they are never hit.

Please find an example below. I'd like to stop the program 
if I get an interrupt, everything looks okay. But break 
command sets breakpoint at 0xbfc00384 instead of 0xbfc00380. 
Is this a bug or feature? I use qemu-system-mipsel with some 
of the pending MIPS patches applied locally. If this is a 
bug, can anybody else reproduce this? Any idea?

Best regards

Dirk

(gdb) info address exception
Symbol "exception" is at 0xbfc00380.
(gdb) list exception
158     .end cache_miss
159
160     .org 0x380
161     .ent exception
162     exception:
163             j       exception_handler
164             nop
165     .end exception
166
167     /****************************************************
(gdb) x/2i 0xbfc00380
0xbfc00380 <exception>: b       0xbfc0046c <exception_handler>
0xbfc00384 <exception+4>:       nop
(gdb) break exception
Breakpoint 1 at 0xbfc00384: file crt0.S, line 163.
(gdb)

Re: [Qemu-devel] setting MIPS gdb breakpoints have wrong offsets

[Stefan Weil]

Hi Dirk,

when I set a breakpoint to address 0x80000180 ("b *0x80000180"), this
works as expected. So do breakpoints to symbolic addresses in the
Linux kernel.

"info breakpoints" shows address 0xffffffff80000180 for the first example.

Maybe "b *0xbfc00380" works for your case. If it does, your mips-gdb
is somehow strange.

Regards
Stefan


Dirk Behme schrieb:

> Hi,
>
> I just tried to debug some simple MIPS code using qemu-system-mipsel 
> by setting some breakpoints. If I use gdb's break command with symbol 
> names the breakpoints are set at offsets and therefore they are never 
> hit.
>
> Please find an example below. I'd like to stop the program if I get an 
> interrupt, everything looks okay. But break command sets breakpoint at 
> 0xbfc00384 instead of 0xbfc00380. Is this a bug or feature? I use 
> qemu-system-mipsel with some of the pending MIPS patches applied 
> locally. If this is a bug, can anybody else reproduce this? Any idea?
>
> Best regards
>
> Dirk

Re: [Qemu-devel] setting MIPS gdb breakpoints have wrong offsets

[Daniel Jacobowitz]

On Sun, Jun 11, 2006 at 10:56:51PM +0200, Stefan Weil wrote:
> Hi Dirk,
> 
> when I set a breakpoint to address 0x80000180 ("b *0x80000180"), this
> works as expected. So do breakpoints to symbolic addresses in the
> Linux kernel.
> 
> "info breakpoints" shows address 0xffffffff80000180 for the first example.
> 
> Maybe "b *0xbfc00380" works for your case. If it does, your mips-gdb
> is somehow strange.

This means that GDB has (mistakenly) decided that the first assembly
instruction in the function is part of a standard function prologue;
feel free to report a GDB bug.

-- 
Daniel Jacobowitz
CodeSourcery