From: Linus Walleij <linus.walleij@linaro.org>
To: Tomislav Novak <tnovak@fb.com>
Cc: Will Deacon <will@kernel.org>,
Russell King <linux@armlinux.org.uk>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@kernel.org>, Namhyung Kim <namhyung@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
linux-arm-kernel@lists.infradead.org,
linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH] ARM: perf: Fix stacktraces for tracepoint events in THUMB2 kernels
Date: Thu, 22 Sep 2022 10:57:11 +0200 [thread overview]
Message-ID: <CACRpkdZZFx3W3EHZh30FnQ+xH9ub_S7DZdGLJFQ_wBVN5EBVwA@mail.gmail.com> (raw)
In-Reply-To: <20220920230728.2617421-1-tnovak@fb.com>
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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next prev parent reply other threads:[~2022-09-22 9:19 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
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 [this message]
2022-09-23 15:05 ` Tomislav Novak
2022-10-03 21:56 ` Linus Walleij
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