On Thu, May 28, 2020 at 09:05:08AM +0100, Peter Smith wrote: > I suggest using Arm if you need a frame pointer, and disable the > frame pointer if you want/need to use Thumb. My understanding is that > runtime unwinding using the frame pointer in Thumb is already difficult > due to Arm and Thumb functions using different registers for the frame > pointer.
IIRC from the Thumb-2 kernel porting days, even in the absence of ARM/Thumb interworking, the Thumb-2 frame pointer was pretty useless for unwinding since it points to the bottom of the current stack frame (the reason I think is that some LDR/STR instructions with negative indexing are not available). So finding the previous frame pointer was not possible and had to rely on the exception unwinding information. -- Catalin
