Messages in this thread | | | Subject | Re: [PATCH] perf symbol: Fix kernel symbol address display | From | Thomas Richter <> | Date | Mon, 27 Apr 2020 14:23:01 +0200 |
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On 4/24/20 8:23 PM, Arnaldo Carvalho de Melo wrote: > 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 >
Yes, it is not easy these days. I just wanted to make sure this patch is not lost. I already have been asked when this will be fixed.
-- 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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