* [PATCH] ARM: perf: Fix stacktraces for tracepoint events in THUMB2 kernels
@ 2022-09-20 23:07 Tomislav Novak
2022-09-22 8:57 ` Linus Walleij
0 siblings, 1 reply; 4+ messages in thread
From: Tomislav Novak @ 2022-09-20 23:07 UTC (permalink / raw)
To: Will Deacon
Cc: Russell King, Mark Rutland, Alexander Shishkin, Jiri Olsa,
Namhyung Kim, Peter Zijlstra, Ingo Molnar,
Arnaldo Carvalho de Melo, linux-arm-kernel, linux-perf-users,
linux-kernel, Tomislav Novak
Store the frame address where arm_get_current_stackframe() looks for it
(ARM_r7 instead of ARM_fp if CONFIG_THUMB2_KERNEL=y). Otherwise frame->fp
gets set to 0, causing unwind_frame() to fail.
# bpftrace -e 't:sched:sched_switch { @[kstack] = count(); exit(); }'
Attaching 1 probe...
@[
__schedule+1059
]: 1
A typical first unwind instruction is 0x97 (SP = R7), so after executing
it SP ends up being 0 and -URC_FAILURE is returned.
unwind_frame(pc = ac9da7d7 lr = 00000000 sp = c69bdda0 fp = 00000000)
unwind_find_idx(ac9da7d7)
unwind_exec_insn: insn = 00000097
unwind_exec_insn: fp = 00000000 sp = 00000000 lr = 00000000 pc = 00000000
With this patch:
# bpftrace -e 't:sched:sched_switch { @[kstack] = count(); exit(); }'
Attaching 1 probe...
@[
__schedule+1059
__schedule+1059
schedule+79
schedule_hrtimeout_range_clock+163
schedule_hrtimeout_range+17
ep_poll+471
SyS_epoll_wait+111
sys_epoll_pwait+231
__ret_fast_syscall+1
]: 1
Signed-off-by: Tomislav Novak <tnovak@fb.com>
---
arch/arm/include/asm/perf_event.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm/include/asm/perf_event.h b/arch/arm/include/asm/perf_event.h
index 4f9dec489931..c5d27140834e 100644
--- a/arch/arm/include/asm/perf_event.h
+++ b/arch/arm/include/asm/perf_event.h
@@ -21,7 +21,7 @@ extern unsigned long perf_misc_flags(struct pt_regs *regs);
#define perf_arch_fetch_caller_regs(regs, __ip) { \
(regs)->ARM_pc = (__ip); \
- (regs)->ARM_fp = (unsigned long) __builtin_frame_address(0); \
+ frame_pointer((regs)) = (unsigned long) __builtin_frame_address(0); \
(regs)->ARM_sp = current_stack_pointer; \
(regs)->ARM_cpsr = SVC_MODE; \
}
--
2.30.2
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^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] ARM: perf: Fix stacktraces for tracepoint events in THUMB2 kernels
2022-09-20 23:07 [PATCH] ARM: perf: Fix stacktraces for tracepoint events in THUMB2 kernels Tomislav Novak
@ 2022-09-22 8:57 ` Linus Walleij
2022-09-23 15:05 ` Tomislav Novak
0 siblings, 1 reply; 4+ messages in thread
From: Linus Walleij @ 2022-09-22 8:57 UTC (permalink / raw)
To: Tomislav Novak
Cc: Will Deacon, Russell King, Mark Rutland, Alexander Shishkin,
Jiri Olsa, Namhyung Kim, Peter Zijlstra, Ingo Molnar,
Arnaldo Carvalho de Melo, linux-arm-kernel, linux-perf-users,
linux-kernel, Arnd Bergmann
On Wed, Sep 21, 2022 at 1:19 AM Tomislav Novak <tnovak@fb.com> wrote:
> Store the frame address where arm_get_current_stackframe() looks for it
> (ARM_r7 instead of ARM_fp if CONFIG_THUMB2_KERNEL=y). Otherwise frame->fp
> gets set to 0, causing unwind_frame() to fail.
>
> # bpftrace -e 't:sched:sched_switch { @[kstack] = count(); exit(); }'
> Attaching 1 probe...
> @[
> __schedule+1059
> ]: 1
>
> A typical first unwind instruction is 0x97 (SP = R7), so after executing
> it SP ends up being 0 and -URC_FAILURE is returned.
>
> unwind_frame(pc = ac9da7d7 lr = 00000000 sp = c69bdda0 fp = 00000000)
> unwind_find_idx(ac9da7d7)
> unwind_exec_insn: insn = 00000097
> unwind_exec_insn: fp = 00000000 sp = 00000000 lr = 00000000 pc = 00000000
>
> With this patch:
>
> # bpftrace -e 't:sched:sched_switch { @[kstack] = count(); exit(); }'
> Attaching 1 probe...
> @[
> __schedule+1059
> __schedule+1059
> schedule+79
> schedule_hrtimeout_range_clock+163
> schedule_hrtimeout_range+17
> ep_poll+471
> SyS_epoll_wait+111
> sys_epoll_pwait+231
> __ret_fast_syscall+1
> ]: 1
>
> Signed-off-by: Tomislav Novak <tnovak@fb.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Can you put this patch into Russell's patch tracker please?
https://www.armlinux.org.uk/developer/patches/
BTW: what is this interesting CONFIG_THUMB2_KERNEL target
that Facebook/Meta is working on? (It's OK if you can't tell, just
curious.)
Yours,
Linus Walleij
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linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] ARM: perf: Fix stacktraces for tracepoint events in THUMB2 kernels
2022-09-22 8:57 ` Linus Walleij
@ 2022-09-23 15:05 ` Tomislav Novak
2022-10-03 21:56 ` Linus Walleij
0 siblings, 1 reply; 4+ messages in thread
From: Tomislav Novak @ 2022-09-23 15:05 UTC (permalink / raw)
To: Linus Walleij
Cc: Will Deacon, Russell King, Mark Rutland, Alexander Shishkin,
Jiri Olsa, Namhyung Kim, Peter Zijlstra, Ingo Molnar,
Arnaldo Carvalho de Melo, linux-arm-kernel, Arnd Bergmann
On Thu, Sep 22, 2022 at 10:57:11AM +0200, Linus Walleij wrote:
> Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
>
> Can you put this patch into Russell's patch tracker please?
Thanks! Done: https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9250/1
This bug came up while I was testing another patch[1] to make sure it doesn't
break stack unwinding in Thumb-2 builds.
[1] https://lore.kernel.org/r/20220921002446.3096120-1-tnovak@fb.com/
--
T.
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] ARM: perf: Fix stacktraces for tracepoint events in THUMB2 kernels
2022-09-23 15:05 ` Tomislav Novak
@ 2022-10-03 21:56 ` Linus Walleij
0 siblings, 0 replies; 4+ messages in thread
From: Linus Walleij @ 2022-10-03 21:56 UTC (permalink / raw)
To: Tomislav Novak
Cc: Will Deacon, Russell King, Mark Rutland, Alexander Shishkin,
Jiri Olsa, Namhyung Kim, Peter Zijlstra, Ingo Molnar,
Arnaldo Carvalho de Melo, linux-arm-kernel, Arnd Bergmann
On Fri, Sep 23, 2022 at 5:06 PM Tomislav Novak <tnovak@meta.com> wrote:
> On Thu, Sep 22, 2022 at 10:57:11AM +0200, Linus Walleij wrote:
> > Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
> >
> > Can you put this patch into Russell's patch tracker please?
>
> Thanks! Done: https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9250/1
>
> This bug came up while I was testing another patch[1] to make sure it doesn't
> break stack unwinding in Thumb-2 builds.
>
> [1] https://lore.kernel.org/r/20220921002446.3096120-1-tnovak@fb.com/
That's what I call a job well done, and exactly the walking an extra mile
spirit that we value in developers!
Thanks!
Yours,
Linus Walleij
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linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 4+ messages in thread
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2022-09-20 23:07 [PATCH] ARM: perf: Fix stacktraces for tracepoint events in THUMB2 kernels Tomislav Novak
2022-09-22 8:57 ` Linus Walleij
2022-09-23 15:05 ` Tomislav Novak
2022-10-03 21:56 ` Linus Walleij
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