From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnaldo Carvalho de Melo Subject: Re: [PATCH] perf symbol: Fix kernel symbol address display Date: Fri, 24 Apr 2020 15:23:36 -0300 Message-ID: <20200424182336.GO19437@kernel.org> References: <20200415070744.59919-1-tmricht@linux.ibm.com> <20200420204617.GA23638@kernel.org> <475a5c86-2be3-4f12-56f3-7bd6587e8ec3@linux.ibm.com> <20200424150631.GN19437@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Thomas Richter Cc: Arnaldo Carvalho de Melo , linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, gor@linux.ibm.com, sumanthk@linux.ibm.com, heiko.carstens@de.ibm.com List-Id: linux-perf-users.vger.kernel.org Em Fri, Apr 24, 2020 at 08:01:22PM +0200, Thomas Richter escreveu: > On 4/24/20 5:06 PM, Arnaldo Carvalho de Melo wrote: > > 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@five perf]$ readelf -sW /usr/lib64/libc-2.30.so | grep strlen_avx2 > >>> 24371: 0000000000161810 414 FUNC LOCAL DEFAULT 15 __strlen_avx2 > >>> [acme@five 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? > > > > I think there is a misunderstanding. > > Your example above refers to libc, which shows the addresses > correctly (on x86 and s390). I was refering to the kernel dso. > The issue only shows up on the kernel DSO (vmlinux and kallsyms) > > When I use the -v option (or 'V' in TUI) I get this > > 3.55% find /lib/modules/.../build/vmlinux 0xf11ec v [k] check_chain_key > ^^^^^^^ > This address is not correct as compared to readelf on vmlinux file: > > [root@m35lp76 linux]# readelf -sW vmlinux| fgrep check_chain_key > 20698: 00000000001f0c70 486 FUNC LOCAL DEFAULT 1 check_chain_key > [root@m35lp76 linux]# > > The problem are the mapping functions with are applied for the kernel DSO. > In dso__process_kernel_symbol() the mapping is adjusted (around line 903) > and function hist_entry_iter_add() saves the modified address in the > struct hist_entry->ip. This address is used from now on and printed. > > Let me know and I will double check this and rework the commit message > as it was not good enough. Yeah, this may be me not understanding something right, I saw this was a corner case, that only happens in debug mode (ok, better provide good info here...), so I haven't devoted more than cursory attention to this and may be making a bad judgement, so I thought that since this doesn't seems urgent, better leave it to when I manage to have solid time to devote to this or someone else looks at this. Sorry, but these have been difficult time for everybody, and I fear, for me, I have to prioritise all the time. - Arnaldo > Thanks. > > > > 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? > > > > -- > 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