linux-kernel - Re: [PATCH] perf symbol: Fix kernel symbol address display

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Message-ID: <20200424150631.GN19437@kernel.org>
Date:   Fri, 24 Apr 2020 12:06:31 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Thomas Richter <tmricht@...ux.ibm.com>
Cc:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        gor@...ux.ibm.com, sumanthk@...ux.ibm.com,
        heiko.carstens@...ibm.com
Subject: Re: [PATCH] perf symbol: Fix kernel symbol address display

Em Fri, Apr 24, 2020 at 02:37:01PM +0200, Thomas Richter escreveu:
> On 4/20/20 10:46 PM, Arnaldo Carvalho de Melo wrote:
> > Em Wed, Apr 15, 2020 at 09:07:44AM +0200, Thomas Richter escreveu:
> >> Running commands
> >>
> >>    ./perf record -e rb0000 -- find .
> >>    ./perf report -v
> > 
> > Or when pressing 'V' in the TUI.
> >  
> >> reveals symbol names and its addresses. There is a mismatch between
> > 
> > Yeah, an address that at some point was put there to help with debugging
> > the symbol resolution, IIRC how it looked like when looking at
> > 
> >   readelf -sW vmlinux
> > 
> > Or any other DSO, for instance, for a glibc symbol here:
> > 
> > Using 'perf report -s pid,dso,sym' then pressing 'V':
> > 
> >    1.55%    20325:perf  /usr/lib64/libc-2.30.so   0x161825   B [.] __strlen_avx2
> > 
> > [acme@...e perf]$ readelf -sW /usr/lib64/libc-2.30.so | grep strlen_avx2
> >  24371: 0000000000161810   414 FUNC    LOCAL  DEFAULT   15 __strlen_avx2
> > [acme@...e perf]$ 
> > 
> > Can you check if doing in /lib/modules/.../build/vmlinux produces what
> > appears when 'V' is in place?
> > 
> > And perhaps we can also show the DSO offset and the rip as it gets laid
> > out in memory in the end? So we have all the informations?
> > 
> > - Arnaldo
> > 
> 
> Arnaldo,
> 
> having verified this also works in the TUI mode using 'V', are you going to pick
> this patch?

That would be a change in behaviour, the original intent was to show the
value one would get from the ELF symbol table, isn't that the case?

That is why I asked if you would think that providing the information
you want, which is matching to what is in kallsyms, would be
interesting, which I think it is, but how? showing the vmlinux offset
somehow?
 
> Thanks
> 
> 
> -- 
> Thomas Richter, Dept 3252, IBM s390 Linux Development, Boeblingen, Germany
> --
> Vorsitzender des Aufsichtsrats: Matthias Hartmann
> Geschäftsführung: Dirk Wittkopp
> Sitz der Gesellschaft: Böblingen / Registergericht: Amtsgericht Stuttgart, HRB 243294

-- 

- Arnaldo