linux-kernel - Re: Getting empty callchain from perf_callchain

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Message-ID: <20190517091044.GM2606@hirez.programming.kicks-ass.net>
Date:   Fri, 17 May 2019 11:10:44 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kairui Song <kasong@...hat.com>
Cc:     Song Liu <songliubraving@...com>,
        lkml <linux-kernel@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: Getting empty callchain from perf_callchain_kernel()

On Fri, May 17, 2019 at 04:15:39PM +0800, Kairui Song wrote:
> Hi, I think the actual problem is that bpf_get_stackid_tp (and maybe
> some other bfp functions) is now broken, or, strating an unwind
> directly inside a bpf program will end up strangely. It have following
> kernel message:

Urgh, what is that bpf_get_stackid_tp() doing to get the regs? I can't
follow.