Problem with GDB when debugging IRQ handlers

[dbaryshkov@gmail.com (Dmitry Eremin-Solenikov)]

On 6/28/11, Catalin Marinas <catalin.marinas@arm.com> wrote:
> On Tue, Jun 28, 2011 at 04:45:52PM +0100, Dmitry Eremin-Solenikov wrote:
>> Here is a part of gdb log generated using the attached patch:
> [...]
>> #11 0xc0033810 in kernel_thread_helper ()
>> #12 0xc0033810 in kernel_thread_helper ()
>> Backtrace stopped: previous frame identical to this frame (corrupt stack?)
>
> Maybe you can add something similar to the kernel_thread_helper in
> arch/arm/kernel/process.c? I'm not sure whether there is something like
> .cantunwind (as for the kernel unwinding information).
>
>> diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
>> index e8d8856..44daf40 100644
>> --- a/arch/arm/kernel/entry-armv.S
>> +++ b/arch/arm/kernel/entry-armv.S
>> @@ -28,6 +28,7 @@
>>  #include "entry-header.S"
>>  #include <asm/entry-macro-multi.S>
>>
>> +	.cfi_sections	.debug_frame
>>  /*
>>   * Interrupt handling.  Preserves r7, r8, r9
>>   */
>> @@ -113,6 +114,7 @@ ENDPROC(__und_invalid)
>>
>>  	.macro	svc_entry, stack_hole=0
>>   UNWIND(.fnstart		)
>> +	.cfi_startproc
>>   UNWIND(.save {r0 - pc}		)
>>  	sub	sp, sp, #(S_FRAME_SIZE + \stack_hole - 4)
>>  #ifdef CONFIG_THUMB2_KERNEL
>> @@ -146,6 +148,24 @@ ENDPROC(__und_invalid)
>>  	@  r4 - orig_r0 (see pt_regs definition in ptrace.h)
>>  	@
>>  	stmia	r5, {r0 - r4}
>> +	.cfi_def_cfa_offset S_PC + 4
>> +	.cfi_offset 14, -4
>> +#define	CFI_REG_OFF(r) .cfi_offset r, (r - 16) * 4
>> +	CFI_REG_OFF(13)
>> +	CFI_REG_OFF(12)
>> +	CFI_REG_OFF(11)
>> +	CFI_REG_OFF(10)
>> +	CFI_REG_OFF(9)
>> +	CFI_REG_OFF(8)
>> +	CFI_REG_OFF(7)
>> +	CFI_REG_OFF(6)
>> +	CFI_REG_OFF(5)
>> +	CFI_REG_OFF(4)
>> +	CFI_REG_OFF(3)
>> +	CFI_REG_OFF(2)
>> +	CFI_REG_OFF(1)
>> +	CFI_REG_OFF(0)
>> +#undef CFI_REG_OFF
>>  	.endm
>
> Do we need all the registers in here for gdb stack unwinding? In general
> we would only need LR, SP and FP.

CFI info isn't only related to stack unwinding. IIUC (I'll have to run
more experiments)
these instrutions will help me to get correct variables/arguments
values in the before-exception stack frames.

>
> --
> Catalin
>
>


-- 
With best wishes
Dmitry