linux-kernel - Re: [RFC 0/4] perf tool: Fix non-".text" symbol resolution for kernel modules

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Message-ID: <760acfd9-26a0-e028-bc29-004be0b2620c@amd.com>
Date:   Tue, 10 Jan 2023 14:13:53 +0530
From:   Ravi Bangoria <ravi.bangoria@....com>
To:     Adrian Hunter <adrian.hunter@...el.com>, acme@...nel.org
Cc:     jolsa@...nel.org, namhyung@...nel.org, irogers@...gle.com,
        kan.liang@...ux.intel.com, peterz@...radead.org,
        mark.rutland@....com, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, james.clark@....com,
        german.gomez@....com, leo.yan@...aro.org,
        alexey.v.bayduraev@...ux.intel.com,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        sandipan.das@....com, ananth.narayan@....com,
        santosh.shukla@....com, Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [RFC 0/4] perf tool: Fix non-".text" symbol resolution for kernel
 modules

Hi Adrian,

On 10-Jan-23 12:05 PM, Adrian Hunter wrote:
> On 10/01/23 07:58, Ravi Bangoria wrote:
>> Kernel module elf contains executable code in non-".text" sections as
>> well, for ex: ".noinstr.text". Plus, kernel module's memory layout
>> differs from it's binary layout because .ko elf does not contain
>> program header table.
> 
> Have you looked at using perf record --kcore option.

Nice! We can also use --kallsyms with perf report and it resolves symbols
fine.

But what about normal perf record/report? Why I'm enforcing on normal perf-
record/report is because, generally user don't specify these options, esp if
he has root privileges, he expects symbol-resolution should just work fine.
But when he sees inconsistency in symbol-resolution of the same kernel module,
he will be clueless of what's missing. This patchset is trying to solve it,
although I too feel adding section specific maps to perf.data is overkill as
--kcore or --kallsyms can also resolve those symbols.

Thanks for your feedback,
Ravi