linux-kernel - Re: [PATCH v2] perf/x86: always include regs->ip in callchain

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Date:   Thu, 23 May 2019 14:06:44 +0800
From:   Kairui Song <kasong@...hat.com>
To:     Song Liu <songliubraving@...com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        bpf@...r.kernel.org, Kernel Team <kernel-team@...com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2] perf/x86: always include regs->ip in callchain

On Thu, May 23, 2019 at 1:34 PM Song Liu <songliubraving@...com> wrote:
>
> Commit d15d356887e7 removes regs->ip for !perf_hw_regs(regs) case. This
> patch adds regs->ip back.
>
> Fixes: d15d356887e7 ("perf/x86: Make perf callchains work without CONFIG_FRAME_POINTER")
> Cc: Kairui Song <kasong@...hat.com>
> Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
> Signed-off-by: Song Liu <songliubraving@...com>
> ---
>  arch/x86/events/core.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index f315425d8468..7b8a9eb4d5fd 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -2402,9 +2402,9 @@ perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *re
>                 return;
>         }
>
> +       if (perf_callchain_store(entry, regs->ip))
> +               return;
>         if (perf_hw_regs(regs)) {
> -               if (perf_callchain_store(entry, regs->ip))
> -                       return;
>                 unwind_start(&state, current, regs, NULL);
>         } else {
>                 unwind_start(&state, current, NULL, (void *)regs->sp);
> --
> 2.17.1
>

Hi, this will make !perf_hw_regs(regs) case print a double first level
stack trace, which is wrong. And the actual problem that unwinder give
empty calltrace in bpf is still not fixed.

-- 
Best Regards,
Kairui Song