linux-kernel - [PATCH v2 0/3] tools/perf: Fix perf probe crash by clang DWARF5 file

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Message-Id: <166731050151.2100653.8202870942871353491.stgit@devnote3>
Date:   Tue,  1 Nov 2022 22:48:21 +0900
From:   "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
To:     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,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: [PATCH v2 0/3] tools/perf: Fix perf probe crash by clang DWARF5 file

Hi,

Here is the 2nd version of the patches for perf probe which improves the
robustness against clang DWARF5 file.

Since the Clang generates a bit different DWARF5 file, the perf probe
crashes or failes to analyze it. There are actually fragile code against
it, so I fixed it ([1/3]) to avoid crash by SEGV. And make it accepts
Clang's DWARF5 file ([2/3],[3/3]).

Without this series, the perf probe crashes with the DWARF5 file
which generated by clang as below;

  $ ./perf probe -k $BIN_PATH/vmlinux -s $SRC_PATH -L vfs_read:10
  Segmentation fault

This series fixes it to handle such file correctly;

  $ ./perf probe -k $BIN_PATH/vmlinux -s $SRC_PATH -L vfs_read:10
  <vfs_read@...C_PATH/fs/read_write.c:10>

       11         ret = rw_verify_area(READ, file, pos, count);
       12         if (ret)
                           return ret;

On the DWARF5 specification, Sec 2.14, there is
"The value 0 indicates that no source file has been specified."
for DW_AT_decl_file, but clang generated DWARF5 will use the value 0.

This issue is discussed on DWARF std ML;
https://www.mail-archive.com/dwarf-discuss@lists.dwarfstd.org/msg00884.html

And suggested that removing this part from the specification.
http://wiki.dwarfstd.org/index.php?title=DWARF5_Line_Table_File_Numbers

So as far as I understand, this is out of standard at this moment,
but the standard itself has a discussion on this part. And maybe updated
as currently clang does in the next release/revision.

Thank you,

---

Masami Hiramatsu (Google) (3):
      tools/perf: Fix to avoid crashing if DW_AT_decl_file is NULL
      tools/perf: Fix to use dwarf_attr_integrate for generic attr accessor
      tools/perf: Fix to get declared file name from clang DWARF5

 tools/perf/util/dwarf-aux.c    |   58 ++++++++++++++++++++++++++++------------
 tools/perf/util/dwarf-aux.h    |    3 ++
 tools/perf/util/probe-finder.c |   37 +++++++++++++++++---------
 3 files changed, 68 insertions(+), 30 deletions(-)

--
Masami Hiramatsu (Google) <mhiramat@...nel.org>