linux-kernel - Re: [PATCH] perf symbol: ignore $a/$d symbols for ARM modules

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Date:   Sat, 6 Nov 2021 16:48:04 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     James Clark <james.clark@....com>
Cc:     Lexi Shao <shaolexi@...wei.com>, linux-perf-users@...r.kernel.org,
        linux-kernel@...r.kernel.org, mark.rutland@....com,
        peterz@...radead.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        namhyung@...nel.org, qiuxi1@...wei.com, nixiaoming@...wei.com,
        wangbing6@...wei.com
Subject: Re: [PATCH] perf symbol: ignore $a/$d symbols for ARM modules

Em Thu, Oct 28, 2021 at 09:44:26AM +0100, James Clark escreveu:
> 
> 
> On 27/10/2021 10:52, Lexi Shao wrote:
> > On ARM machine, kernel symbols from modules can be resolved to $a
> > instead of printing the actual symbol name. Ignore symbols starting with
> > "$" when building kallsyms rbtree.
> > 
> > A sample stacktrace is shown as follows:
> > 
> > c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms])
> > bf4a66d8 $a+0x78 ([test_module])
> > c0a4f5f4 kthread+0x15c ([kernel.kallsyms])
> > c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms])
> > 
> > On ARM machine, $a/$d symbols are used by the compiler to mark the
> > beginning of code/data part in code section. These symbols are filtered
> > out when linking vmlinux(see scripts/kallsyms.c ignored_prefixes), but
> > are left on modules. So there are $a symbols in /proc/kallsyms which
> > share the same addresses with the actual module symbols and confuses perf
> > when resolving symbols.
> > 
> > After this patch, the module symbol name is printed:
> > 
> > c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms])
> > bf4a66d8 test_func+0x78 ([test_module])
> > c0a4f5f4 kthread+0x15c ([kernel.kallsyms])
> > c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms])
> > 
> > Signed-off-by: Lexi Shao <shaolexi@...wei.com>
> 
> Reviewed-by: James Clark <james.clark@....com>

Thanks, applied.

- Arnaldo