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Date:   Wed, 22 May 2019 12:45:17 -0500
From:   Josh Poimboeuf <jpoimboe@redhat.com>
To:     Alexei Starovoitov <ast@fb.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Kairui Song <kasong@redhat.com>,
        Song Liu <songliubraving@fb.com>,
        lkml <linux-kernel@vger.kernel.org>,
        Kernel Team <Kernel-team@fb.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        "bpf@vger.kernel.org" <bpf@vger.kernel.org>
Subject: Re: Getting empty callchain from perf_callchain_kernel()
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On Wed, May 22, 2019 at 02:49:07PM +0000, Alexei Starovoitov wrote:
> The one that is broken is prog_tests/stacktrace_map.c
> There we attach bpf to standard tracepoint where
> kernel suppose to collect pt_regs before calling into bpf.
> And that's what bpf_get_stackid_tp() is doing.
> It passes pt_regs (that was collected before any bpf)
> into bpf_get_stackid() which calls get_perf_callchain().
> Same thing with kprobes, uprobes.

Is it trying to unwind through ___bpf_prog_run()?

If so, that would at least explain why ORC isn't working.  Objtool
currently ignores that function because it can't follow the jump table.

-- 
Josh