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From:   Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Date:   Fri, 29 Nov 2019 12:14:36 -0300
To:     Jiri Olsa <jolsa@redhat.com>
Cc:     Ivan Babrou <ivan@cloudflare.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-perf-users@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Namhyung Kim <namhyung@kernel.org>,
        kernel-team <kernel-team@cloudflare.com>
Subject: Re: perf is unable to read dward from go programs
Message-ID: <20191129151436.GB26963@kernel.org>
References: <CABWYdi2jvPUq128XDv_VbY=vFknFyJHbUR=0_K9WuA0mFTkPvg@mail.gmail.com>
 <CABWYdi3k9QvFOEd_hFG16LVE=BiokO4hWp50nZcxYwbWfxeE3g@mail.gmail.com>
 <20191129134929.GA26903@krava>
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Em Fri, Nov 29, 2019 at 02:49:29PM +0100, Jiri Olsa escreveu:
> On Wed, Nov 27, 2019 at 01:15:20PM -0800, Ivan Babrou wrote:
> > There were no response in linux-perf-users@, so I think it's fair to
> > ask maintainers.
> > 
> > On Fri, Nov 8, 2019 at 3:53 PM Ivan Babrou <ivan@cloudflare.com> wrote:
> > >
> > > I have a simple piece of code that burns CPU for 1s:
> > >
> > > * https://gist.github.com/bobrik/cf022ff6950d09032fa13a984e2272ed
> > >
> > > I can build it just fine: go build -o /tmp/burn burn.go
> > >
> > > And I can see correct stacks if I record with fp:
> > >
> > > perf record -e cpu-clock -g -F 99 /tmp/burn
> > >
> > > But if I record with gwarf:
> > >
> > > perf record -e cpu-clock -g -F 99 --call-graph dwarf /tmp/burn
> > >
> > > Then stacks are lost with the following complaints during "perf script":
> > >
> > > BFD: Dwarf Error: found dwarf version '376', this reader only handles
> > > version 2, 3 and 4 information.
> > > BFD: Dwarf Error: found dwarf version '31863', this reader only
> > > handles version 2, 3 and 4 information.
> > > BFD: Dwarf Error: found dwarf version '65271', this reader only
> > > handles version 2, 3 and 4 information.
> > > BFD: Dwarf Error: found dwarf version '289', this reader only handles
> > > version 2, 3 and 4 information.
> 
> hi,
> the binary generated by go has compressed debug info (on my setup)
> and libunwind (default dwarf unwinder) does not seem to support that
> 
> but when I compile perf with libdw unwind support:
> 
>   $ make DEBUG=1 VF=1 NO_LIBUNWIND=1
> 
> I'm getting proper backtraces (below), maybe it's time to change
> the default dwarf unwinder ;-)

we have some 'perf test' entries testing the unwinding routines, can you
please check if those pass when switching to libdw's unwinder?

- Arnaldo
 
> thanks,
> jirka
> 
> 
> ---
>     51.63%  ex       ex                [.] crypto/sha512.blockAVX2
>             |
>             ---crypto/sha512.blockAVX2
>                |          
>                 --51.48%--crypto/sha512.block
>                           crypto/sha512.(*digest).Write
>                           crypto/sha512.(*digest).checkSum
>                           crypto/sha512.(*digest).Sum
>                           main.burn
>                           main.main
>                           runtime.main
>                           runtime.goexit
> 
>     11.55%  ex       ex                [.] runtime.mallocgc
>             |
>             ---runtime.mallocgc
>                |          
>                |--7.45%--runtime.newobject
>                |          |          
>                |           --7.45%--main.burn
>                |                     main.main
>                |                     runtime.main
>                |                     runtime.goexit
>                |          
>                 --3.40%--runtime.growslice
>                           crypto/sha512.(*digest).Sum
>                           main.burn
>                           main.main
>                           runtime.main
>                           runtime.goexit
> 
>      3.69%  ex       ex                [.] crypto/sha512.(*digest).Write
>             |
>             ---crypto/sha512.(*digest).Write
>                |          
>                |--2.91%--crypto/sha512.(*digest).checkSum
>                |          crypto/sha512.(*digest).Sum
>                |          main.burn
>                |          main.main
>                |          runtime.main
>                |          runtime.goexit
>                |          
>                 --0.57%--main.burn
>                           main.main
>                           runtime.main
>                           runtime.goexit
> 
>      3.44%  ex       ex                [.] runtime.memclrNoHeapPointers
>             |
>             ---runtime.memclrNoHeapPointers
>                |          
>                 --2.92%--runtime.(*mheap).alloc
>                           runtime.(*mcentral).grow
>                           runtime.(*mcentral).cacheSpan
>                           runtime.(*mcache).refill
>                           runtime.(*mcache).nextFree
>                           runtime.mallocgc
>                           |          
>                           |--2.27%--runtime.newobject
>                           |          main.burn
>                           |          main.main
>                           |          runtime.main
>                           |          runtime.goexit
>                           |          
>                            --0.64%--runtime.growslice
>                                      crypto/sha512.(*digest).Sum
>                                      main.burn
>                                      main.main
>                                      runtime.main
>                                      runtime.goexit
> ...

-- 

- Arnaldo