On Friday 30 May 2014 17:59:44 Nikolay Borisov wrote:

From: Nikolay Borisov <redacted>

Currently all the code which deals with backtrace support assumes that R11
is the frame-pointer. While this is the case for ARM mode and is explicitly
documented in the AAPCS, this is not the case for THUMB2 mode.

There is no official document requiring that R11 has to be the frame pointer
and GCC uses R7 as FP and given that R7's usage is so intertwined within GCC's
mechanics it is unlikely to change, so fixing backtrace in THUMB2 mode seems
in order.

This patch series rectifies the problem by first fixing the
thread_save_fp macro to reference the correct register. Furthermore, there
a lot of repetetive sequences of code such as :

stackframe.fp = pt_regs->ARM_fp
stackframe.lr = pt_regs->ARM_lr

so introducing a function arm_get_current_stack_frame which both
hides this repetition and also utilizes teh frame_pointer(regs) macro
to reference the correct register depending on the mode.

Finally, change all the call sites so that they utilize the new routine.

Sorry for the stupid question, but does your series relate to the
#warning "TODO: return_address should use unwind tables" that we see
all the time in arch/arm/kernel/return_address.c?

If I remember the story correctly, the problem is that so far we could
never use the frame pointer in thumb2 mode, and nobody has implemented
a version of that function using the arm unwinder.

Are we now able to use the frame pointer after all?

	Arnd