Messages in this thread | | | From | Nick Desaulniers <> | Date | Wed, 21 Aug 2019 19:33:02 -0700 | Subject | Re: [PATCH] ARM: UNWINDER_FRAME_POINTER implementation for Clang |
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On Wed, Aug 21, 2019 at 10:43 AM Nathan Huckleberry <nhuck@google.com> wrote: > > On Tue, Aug 20, 2019 at 2:39 PM Nick Desaulniers > <ndesaulniers@google.com> wrote: > > > > On Tue, Aug 20, 2019 at 12:44 PM Nathan Huckleberry <nhuck@google.com> wrote: ...snip... > > > +tst r1, #0x10 @ 26 or 32-bit mode? > > > +moveq mask, #0xfc000003 > > > > Should we be using different masks for ARM vs THUMB as per the > > reference implementation? > The change that introduces the arm/thumb code looked like a script > that was run over all arm in the kernel. Neither this code nor the > reference solution is compatible with arm, so there's no need for the > change.
Looks like you're referring to commit 8b592783a2e8 ("Thumb-2: Implement the unified arch/arm/lib functions").
Currently, arch/arm/Kconfig.debug has: 57 config UNWINDER_FRAME_POINTER 58 bool "Frame pointer unwinder" 59 depends on !THUMB2_KERNEL && !CC_IS_CLANG
So it looks like UNWINDER_FRAME_POINTER and THUMB2_KERNEL are mutually exclusive. Probably could send a patch cleaning that up. (ie. removing the different masks; essentially removing the hunk from arch/arm/lib/backtrace.S from 8b592783a2e8).
> > > +for_each_frame: tst frame, mask @ Check for address exceptions > > > + bne no_frame > > > + > > > +/* > > > + * sv_fp is the stack frame with the locals for the current considered > > > + * function. > > > + * sv_pc is the saved lr frame the frame above. This is a pointer to a > > > + * code address within the current considered function, but > > > + * it is not the function start. This value gets updated to be > > > + * the function start later if it is possible. > > > + */ > > > +1001: ldr sv_pc, [frame, #4] @ get saved 'pc' > > > +1002: ldr sv_fp, [frame, #0] @ get saved fp > > > > The reference implementation applies the mask to sv_pc and sv_fp. I > > assume we want to, too? > The mask is already applied to both. See for_each_frame:
ah, under the finished_setup label. -- Thanks, ~Nick Desaulniers
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