perf dwarf-aux: Check allowed DWARF Ops
authorNamhyung Kim <namhyung@kernel.org>
Wed, 17 Jan 2024 06:26:57 +0000 (22:26 -0800)
committerNamhyung Kim <namhyung@kernel.org>
Mon, 22 Jan 2024 20:08:20 +0000 (12:08 -0800)
commit55442cc2f22d0727abfecc3a30c605f04acff4b7
tree03a12222b301a734e986bd225980490889edc2a9
parentbc10db8eb8955fbcaf29f75c91147e4e724b740d
perf dwarf-aux: Check allowed DWARF Ops

The DWARF location expression can be fairly complex and it'd be hard
to match it with the condition correctly.  So let's be conservative
and only allow simple expressions.  For now it just checks the first
operation in the list.  The following operations looks ok:

 * DW_OP_stack_value
 * DW_OP_deref_size
 * DW_OP_deref
 * DW_OP_piece

To refuse complex (and unsupported) location expressions, add
check_allowed_ops() to compare the rest of the list.  It seems earlier
result contained those unsupported expressions.  For example, I found
some local struct variable is placed like below.

 <2><43d1517>: Abbrev Number: 62 (DW_TAG_variable)
    <43d1518>   DW_AT_location    : 15 byte block: 91 50 93 8 91 78 93 4 93 84 8 91 68 93 4
        (DW_OP_fbreg: -48; DW_OP_piece: 8;
         DW_OP_fbreg: -8; DW_OP_piece: 4;
         DW_OP_piece: 1028;
         DW_OP_fbreg: -24; DW_OP_piece: 4)

Another example is something like this.

    0057c8be ffffffffffffffff ffffffff812109f0 (base address)
    0057c8ce ffffffff812112b5 ffffffff812112c8 (DW_OP_breg3 (rbx): 0;
                                                DW_OP_constu: 18446744073709551612;
                                                DW_OP_and;
                                                DW_OP_stack_value)

It should refuse them.  After the change, the stat shows:

  Annotate data type stats:
  total 294, ok 158 (53.7%), bad 136 (46.3%)
  -----------------------------------------------------------
          30 : no_sym
          32 : no_mem_ops
          53 : no_var
          14 : no_typeinfo
           7 : bad_offset

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Ian Rogers <irogers@google.com>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20240117062657.985479-10-namhyung@kernel.org
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
tools/perf/util/dwarf-aux.c