linux-kernel - Re: [PATCH v2 3/3] tools/perf: Fix to get declared file name from clang DWARF5

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Date:   Fri, 9 Jun 2023 14:21:30 +0200
From:   Georg Müller <georgmueller@....net>
To:     "Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v2 3/3] tools/perf: Fix to get declared file name from
 clang DWARF5

Hi,

Am 01.11.22 um 14:48 schrieb Masami Hiramatsu (Google):
> From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
>
> Fix to get the declared file name even if it uses file index 0
> in DWARF5, using custom die_get_decl_file() function.
>

this patch breaks perf probe on fedora 38.

I was trying to a add a probe to systemd-logind using kernel-6.3.6-200.fc38.x86_64 with kernel-tools-6.3.3-200.fc38.x86_64.

When trying to add a probe, I get the following message:

# perf probe -x /usr/lib/systemd/systemd-logind --funcs="match_unit_removed"
match_unit_removed

Function exists and was found:

# perf probe -x /usr/lib/systemd/systemd-logind match_unit_removed
A function DIE doesn't have decl_line. Maybe broken DWARF?
A function DIE doesn't have decl_line. Maybe broken DWARF?
Probe point 'match_unit_removed' not found.
   Error: Failed to add events.

When reverting dc9a5d2ccd5c823cc05cafe75fcf19b682d8152c, I was able to add the probe point:

# ./perf probe -x /usr/lib/systemd/systemd-logind match_unit_removed
Added new event:
   probe_systemd:match_unit_removed (on match_unit_removed in /usr/lib/systemd/systemd-logind)

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

	perf record -e probe_systemd:match_unit_removed -aR sleep 1

Probe point is then visible with and without this commit:

# perf probe -l
   probe_systemd:match_unit_removed (on match_unit_removed in /usr/lib/systemd/systemd-logind)
# ./perf probe -l
   probe_systemd:match_unit_removed (on match_unit_removed@...src/login/logind-dbus.c in /usr/lib/systemd/systemd-logind)

Best regards,
Georg