Problem with GDB when debugging IRQ handlers

[Dmitry Eremin-Solenikov]

Hello,

On 27.06.2011 17:27, Russell King - ARM Linux wrote:
> On Mon, Jun 27, 2011 at 04:53:06PM +0400, Dmitry Eremin-Solenikov wrote:
>> I've got into a problem when trying to debug irq handlers on PXA (in
>> qemu). backtrace is really strange from my POV (a target is just a qemu
>> running a bit modified 3.0-rc2 kernel):
> ...
>> Breakpoint 1, handle_level_irq (irq=42, desc=0xc3e06000) at kernel/irq/chip.c:329
>> 329		mask_ack_irq(desc);
>> (gdb) bt
>> #0  handle_level_irq (irq=42, desc=0xc3e06000) at kernel/irq/chip.c:329
>> #1  0xc0085f64 in generic_handle_irq_desc (irq=42) at include/linux/irqdesc.h:111
>> #2  generic_handle_irq (irq=42) at kernel/irq/irqdesc.c:304
>> #3  0xc0033060 in asm_do_IRQ (irq=42, regs=<value optimized out>) at arch/arm/kernel/irq.c:90
>> #4  0xc0033b50 in __irq_svc () at arch/arm/kernel/entry-armv.S:202
>> #5  0xc0033b50 in __irq_svc () at arch/arm/kernel/entry-armv.S:202
>> #6  0xc0033b50 in __irq_svc () at arch/arm/kernel/entry-armv.S:202
>> #7  0xc0033b50 in __irq_svc () at arch/arm/kernel/entry-armv.S:202
>> #8  0xc0033b50 in __irq_svc () at arch/arm/kernel/entry-armv.S:202
>> #9  0xc0033b50 in __irq_svc () at arch/arm/kernel/entry-armv.S:202
>> #10 0xc0033b50 in __irq_svc () at arch/arm/kernel/entry-armv.S:202
>> #11 0xc0033b50 in __irq_svc () at arch/arm/kernel/entry-armv.S:202
>> #12 0xc0033b50 in __irq_svc () at arch/arm/kernel/entry-armv.S:202
>>
>> ... and so on it continues ad infinitum. Is it the expected behaviour?
>> Because I'm pretty much sure that this isn't a desired behaviour.
>
> My guess is that gdb is trying to unwind using the unwind information.
> However, I don't think we actually give the assembler the full information
> to be able to unwind this.  I've no idea how to solve this as I'm no
> expert at the debug info.
>
> We _really_ _do_ want to unwind through this so that we can see the
> parent kernel context information in backtraces - and the fact that
> the kernel itself can unwind through these means we can't tell the
> unwinder not to.
>
> So, no idea.  I think you need someone who knows debug info to sort
> this one out.

Adding gdb ML to cc in the hope to get any assistance.

-- 
With best wishes
Dmitry