linux-kernel - Re: Getting empty callchain from perf_callchain

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Message-ID: <20190524130557.icmofltzzotqvurg@treble>
Date:   Fri, 24 May 2019 08:05:57 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Kairui Song <kasong@...hat.com>, Alexei Starovoitov <ast@...com>,
        Song Liu <songliubraving@...com>,
        lkml <linux-kernel@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>
Subject: Re: Getting empty callchain from perf_callchain_kernel()

On Fri, May 24, 2019 at 10:53:19AM +0200, Peter Zijlstra wrote:
> On Thu, May 23, 2019 at 10:24:13AM -0500, Josh Poimboeuf wrote:
> 
> > Here's the latest version which should fix it in all cases (based on
> > tip/master):
> > 
> >   https://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git/commit/?h=bpf-orc-fix
> 
> That patch suffers an inconsitency, the comment states:
> 
>   'if they have "jump_table" in the name'
> 
> while the actual code implements:
> 
>   'if the name starts with "jump_table"'
> 
> Other than that, I suppose that works just fine ;-)

The thing is, gcc converts a static local variable named "jump_table" to
an ELF symbol with a numbered suffix, something like "jump_table.12345".
But yeah I should at least clarify that in the comment.

-- 
Josh