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Message-ID: <06bf52bd-43eb-74f9-dfb1-470e2e42fe51@amd.com>
Date:   Tue, 10 Jan 2023 14:28:42 +0530
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Subject: Re: [RFC 0/4] perf tool: Fix non-".text" symbol resolution for kernel
 modules
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To:     Adrian Hunter <adrian.hunter@intel.com>, acme@kernel.org
Cc:     jolsa@kernel.org, namhyung@kernel.org, irogers@google.com,
        kan.liang@linux.intel.com, peterz@infradead.org,
        mark.rutland@arm.com, mingo@redhat.com,
        alexander.shishkin@linux.intel.com, james.clark@arm.com,
        german.gomez@arm.com, leo.yan@linaro.org,
        alexey.v.bayduraev@linux.intel.com,
        linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
        sandipan.das@amd.com, ananth.narayan@amd.com,
        santosh.shukla@amd.com, Ravi Bangoria <ravi.bangoria@amd.com>
References: <20230110055859.685-1-ravi.bangoria@amd.com>
 <86f43058-a51a-42c7-4d75-564f0e8eef04@intel.com>
 <760acfd9-26a0-e028-bc29-004be0b2620c@amd.com>
From:   Ravi Bangoria <ravi.bangoria@amd.com>
In-Reply-To: <760acfd9-26a0-e028-bc29-004be0b2620c@amd.com>
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On 10-Jan-23 2:13 PM, Ravi Bangoria wrote:
> 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.

FWIW, what this patchset does is not new. Perf already creates (pseudo) maps
for module elf sections while parsing symbol table: dso__process_kernel_symbol().
But perf does it incorrectly so this patchset is trying to fix it.

Thanks,
Ravi