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

[Masami Hiramatsu (Google)]

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 $SRC_PATH -L vfs_read:10
  <vfs_read@$SRC_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@xxxxxxxxxxxxxxxxxx/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@xxxxxxxxxx>