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

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Date:   Mon, 16 Jan 2023 09:51:27 +0530
From:   Ravi Bangoria <ravi.bangoria@....com>
To:     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, adrian.hunter@...el.com,
        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 all,

On 10-Jan-23 11:28 AM, 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.
> 
> Perf tries to solve it by creating special maps for allocated (SHF_ALLOC)
> elf sections, but perf uses elf addresses for map address range and thus
> these special maps remains unused because no real ip falls into their
> address range.
> 
> Solve this by preparing section specific special maps using addresses
> provided by sysfs /sys/module/.../sections/. Also save these details in
> PERF_RECORD_KMOD_SEC_MAP format in perf.data which can be consumed at
> perf-report time.

Do you guys feel this is worth to fix and I shall continue? Or --kcore /
--kallsyms workarounds are sufficient?

Thanks,
Ravi