Re: [PATCH] arm64: vdso32: force vdso32 to be compiled as -marm

Catalin Marinas
2020-05-28T09:42:00Z

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