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Date: Fri, 24 Apr 2020 20:01:22 +0200 From: Thomas Richter <tmricht@...ux.ibm.com> To: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com> Cc: 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 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@...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? > 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@...lp76 linux]# readelf -sW vmlinux| fgrep check_chain_key 20698: 00000000001f0c70 486 FUNC LOCAL DEFAULT 1 check_chain_key [root@...lp76 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. 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
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