Re: [PATCH 6/8] ARM: clang: Do not relay on lr register for stacktrace

On Tue, Oct 12, 2021 at 7:18 AM Masami Hiramatsu [off-list ref] wrote:

Hi Nick,

On Mon, 11 Oct 2021 11:45:22 -0700
Nick Desaulniers [off-list ref] wrote:

quoted

If I change from CONFIG_UNWINDER_ARM=y to
CONFIG_UNWINDER_FRAME_POINTER=y, before:

# cat /proc/self/stack
[<0>] stack_trace_save_tsk+0x50/0x6c
[<0>] proc_pid_stack+0xa0/0xf8
[<0>] proc_single_show+0x50/0xbc
[<0>] seq_read_iter+0x178/0x4ec
[<0>] seq_read+0x138/0x15c
[<0>] vfs_read+0xd0/0x304
[<0>] ksys_read+0x78/0xd4
[<0>] sys_read+0xc/0x10

after:
# cat /proc/self/stack
[<0>] proc_pid_stack+0xa0/0xf8
[<0>] proc_single_show+0x50/0xbc
[<0>] seq_read_iter+0x178/0x4ec
[<0>] seq_read+0x138/0x15c
[<0>] vfs_read+0xd0/0x304
[<0>] ksys_read+0x78/0xd4
[<0>] sys_read+0xc/0x10
[<0>] __entry_text_start+0x14/0x14
[<0>] 0xffffffff

So I guess this helps the CONFIG_UNWINDER_FRAME_POINTER=y case? (That
final frame address looks wrong, but is potentially yet another bug;
perhaps for clang we need to manually store the previous frame's pc at
a different offset before jumping to __entry_text_start).

Ah, yes. I didn't touch the UNWINDER_ARM. As you may know the
unwind_frame()@arch/arm/kernel/stacktrace.c is compiled only
CONFIG_UNWINDER_FRAME_POINTER=y.

Ah, right, thanks for pointing that out.

quoted

so likely this fixes/improves CONFIG_UNWINDER_FRAME_POINTER=y? Is that correct?

Yes, that is correct.

In that case, additionally:
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

-- 
Thanks,
~Nick Desaulniers

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel