linux-kernel - [BUG?] perf: dwarf unwind doesn't work correctly with -static

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Date:   Mon, 27 Mar 2017 12:39:54 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Kim Phillips <kim.phillips@....com>,
        Will Deacon <will.deacon@....com>,
        He Kuang <hekuang@...wei.com>, Wang Nan <wangnan0@...wei.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Mark Rutland <mark.rutland@....com>,
        <linux-kernel@...r.kernel.org>
Subject: [BUG?] perf: dwarf unwind doesn't work correctly with -static

Hello,

On Fri, 24 Mar 2017 22:00:30 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> On Thu, 23 Mar 2017 22:24:01 -0500
> Kim Phillips <kim.phillips@....com> wrote:
> 
> > On Thu, 23 Feb 2017 16:50:18 +0900
> > Masami Hiramatsu <mhiramat@...nel.org> wrote:
> > 
> > [sorry for the delay, I just saw this]
> > 
> > > perf record -g dwarf (and perf report) doesn't show correct callchain
> > > on aarch64. Here is how to reproduce it.
> > ...
> > > # Samples: 6K of event 'cpu-clock:u'
> > > # Event count (approx.): 1623750000
> > > #
> > > # Children      Self  Command  Shared Object  Symbol                    
> > > # ........  ........  .......  .............  ..........................
> > > #
> > >     17.21%    17.21%  main     main           [.] func2
> > >             |
> > >             ---func2
> > > 
> > >     17.09%    17.09%  main     main           [.] func1
> > >             |
> > >             ---func1
> > > 
> > >     16.67%    16.67%  main     main           [.] main
> > >             |
> > >             ---main
> > > .....
> > > 
> > > So, as you can see, the call graph reported each function has been
> > > called from itself. If I report it with fp as below, perf reported
> > > correct callgraph.
> > ...
> > > I guess there is a bug in libunwind on aarch64 or we missed to pass
> > > the stack data to libunwind. (BTW, it works correctly on arm32)
> > 
> > Trying to replicate this on a debian 9 ("stretch") arm64 box:
> 
> I'm using debian 8 ("jessie"), but I can try debian 9 too.

I've tried debian 9 and found this issue is another reason.

> 2) Build attached program as below
> # gcc -O0 -ggdb3 -funwind-tables -o main main.c

Originally, I reported above, but that is not correct, when I cleaned
up the command line, I missed important piece -- -static.

I've tested several binaries with different gcc, and found that
- Even with linaro-gcc 6.3.1, this issue happened.
- But natively build binary with gcc-6.3 (stretch) I didn't see it.
- Building binary with -static, it happened even with native binary 6.3.
- And I saw this happened even on x86-64 with -static.

So, I think the correct subject is

"perf: dwarf unwind doesn't work correctly with -static"

Thank you,

-- 
Masami Hiramatsu <mhiramat@...nel.org>