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To:     Masami Hiramatsu <mhiramat@kernel.org>
From:   Alexandre Ghiti <alex@ghiti.fr>
Subject: Perf tool regression from 07d369857808
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Sasha Levin <sashal@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org
Message-ID: <2bb02f9b-1413-97c3-684b-104a0fab9144@ghiti.fr>
Date:   Thu, 27 Feb 2020 13:23:19 +0100
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Hi Masami,

The commit 07d369857808 ("perf probe: Fix wrong address verification) 
found its way in kernel 4.19.98 (and debian 10) and I observed some 
regressions when I try to add probes in shared libraries.
The symptoms are:

$ perf probe -f --exec=/home/aghiti/lib/libdpuhw.so --add 
'log_rank_path=log_rank_path rank path:string'
   Failed to find symbol at 0x3bf0
     Error: Failed to add events.

Whereas when I revert this patch, on the same shared library:

$ perf probe -f --exec=/home/aghiti/lib/libdpuhw.so --add 
'log_rank_path=log_rank_path rank path:string'
Added new event:
   probe_libdpuhw:log_rank_path_4 (on log_rank_path in 
/home/aghiti/lib/libdpuhw.so.2020.1.0 with rank path:string)

You can now use it in all perf tools, such as:

	perf record -e probe_libdpuhw:log_rank_path_4 -aR sleep 1

Actually, I noted that this patch reverts a previous patch that stated 
that dwfl_module_addrsym could fail on shared libraries 664fee3dc379 
("perf probe: Do not use dwfl_module_addrsym if dwarf_diename finds 
symbol name").

Let me know if I can be of any help,

Thanks,

Alexandre Ghiti