Fix backtrace support in THUMB2 mode
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Cover letter [PATCH v2 0/7] Fix backtrace support in THUMB2 mode
Quoted 15 lines · On Friday 30 May 2014 17:59:44 Nikolay Borisov wrote:
From: Nikolay Borisov <[email protected]>
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_fpmacro to reference the correct register. Furthermore, there a lot of repetetive sequences of code such as :
Quoted 8 lines
stackframe.fp =
pt_regs->ARM_fp
stackframe.lr =pt_regs->ARM_lrso introducing a function
arm_get_current_stack_framewhich both hides this repetition and also utilizes tehframe_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