linux-kernel - Re: [PATCH 1/3] perf tools: Set proper module name when build-id event found

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Date:   Thu, 1 Jun 2017 00:24:52 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Jiri Olsa <jolsa@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, kernel-team@....com,
        David Ahern <dsahern@...il.com>,
        Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH 1/3] perf tools: Set proper module name when build-id
 event found

On Wed, May 31, 2017 at 09:01:03PM +0900, Namhyung Kim wrote:
> When perf processes build-id event, it creates DSOs with the build-id.
> But it didn't set the module short name (like '[module-name]') so when
> processing a kernel mmap event of the module, it cannot found the DSO as
> it only checks the short names.
> 
> That leads for perf to create a same DSO without the build-id info and
> it'll lookup the system path even if the DSO is already in the build-id
> cache.  After kernel was updated, perf cannot find the DSO  and cannot show
> symbols in it anymore.
> 
> You can see this if you have an old data file (w/ old kernel version):
> 
>   $ perf report -i perf.data.old -v |& grep scsi_mod
>   build id event received for /lib/modules/3.19.2-1-ARCH/kernel/drivers/scsi/scsi_mod.ko.gz : cafe1ce6ca13a98a5d9ed3425cde249e57a27fc1
>   Failed to open /lib/modules/3.19.2-1-ARCH/kernel/drivers/scsi/scsi_mod.ko.gz, continuing without symbols
>   ...
> 
> The second message didn't show the build-id.  With this patch:
> 
>   $ perf report -i perf.data.old -v |& grep scsi_mod
>   build id event received for /lib/modules/3.19.2-1-ARCH/kernel/drivers/scsi/scsi_mod.ko.gz: cafe1ce6ca13a98a5d9ed3425cde249e57a27fc1
>   /lib/modules/3.19.2-1-ARCH/kernel/drivers/scsi/scsi_mod.ko.gz with build id cafe1ce6ca13a98a5d9ed3425cde249e57a27fc1 not found, continuing without symbols
>   ...
> 
> Now it shows the build-id but still cannot load the symbol table.  This
> is a different problem which will be fixed in the next patch.
> 
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>

for all 3:

Acked-by: Jiri Olsa <jolsa@...nel.org>

thanks,
jirka