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Date:   Mon, 16 Jan 2023 19:04:12 +0530
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From:   Ravi Bangoria <ravi.bangoria@amd.com>
Subject: Re: [RFC 3/4] perf tool: Introduce PERF_RECORD_KMOD_SEC_MAP
To:     Adrian Hunter <adrian.hunter@intel.com>
Cc:     acme@kernel.org, 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>
 <20230110055859.685-4-ravi.bangoria@amd.com>
 <cbcb6109-0c23-9270-a534-c4fabdddfbbc@intel.com>
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Hi Adrian,

On 16-Jan-23 11:44 AM, Adrian Hunter wrote:
> On 10/01/23 07:58, Ravi Bangoria wrote:
>> Introduce, perf tool only, synthetic event type PERF_RECORD_KMOD_SEC_MAP.
>> Also add stub code for it. This event will be used to save/restore kernel
>> module section maps to/from perf.data file. This is needed because kernel
>> module elfs does not contain program header table and thus there is no
>> easy way to find out how kernel would have loaded module sections in the
>> memory.
> 
> Currently machine__addnew_module_map() adds a map for a
> module, and then perf_event__synthesize_modules() creates
> an MMAP/MMAP2 event for it.  Why can't we do that for the
> sections?

Do you mean why not use MMAP/MMAP2 for module sections as well?
I thought about that but:
- PERF_RECORD_MMAP has no field which can help segregate normal vs section
  specific maps.
- I can probably introduce special MAP_ flag and use PERF_RECORD_MMAP2. But
  that flag will be non-standard (perf tool only), which is ugly.
- I also need additional hacks while synthesizing section specific MMAP/
  MMAP2 (e.g.: store section name and file path in filename[]) and similar
  hacks while parsing them at perf report time.

So I felt introducing PERF_RECORD_KMOD_SEC_MAP is relatively cleaner approach.

Thanks,
Ravi