[PATCH -tip ] [BUGFIX] perf/probe: Fix perf probe to find correct variable DIE

Masami Hiramatsu
2014-05-29T12:19:43Z

Fix perf probe to find correct variable DIE which has location or
external instance by tracking down the lexical blocks.

Current die_find_variable() expects that the all variable DIEs
which has DW_TAG_variable have a location. However, since recent
dwarf information may have declaration variable DIEs at the
entry of function (subprogram), die_find_variable() returns it.

To solve this problem, it must track down the DIE tree to find
a DIE which has an actual location or a reference for external
instance.

e.g. finding a DIE which origin is <0xdc73>;

<1><11496>: Abbrev Number: 95 (DW_TAG_subprogram)
<11497> DW_AT_abstract_origin: <0xdc42>
<1149b> DW_AT_low_pc : 0x1850
[...]
<2><114cc>: Abbrev Number: 119 (DW_TAG_variable) <- this is a declaration
<114cd> DW_AT_abstract_origin: <0xdc73>
<2><114d1>: Abbrev Number: 119 (DW_TAG_variable)
[...]
<3><115a7>: Abbrev Number: 105 (DW_TAG_lexical_block)
<115a8> DW_AT_ranges : 0xaa0
<4><115ac>: Abbrev Number: 96 (DW_TAG_variable) <- this has a location
<115ad> DW_AT_abstract_origin: <0xdc73>
<115b1> DW_AT_location : 0x486c (location list)

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
---
tools/perf/util/dwarf-aux.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
index 7defd77..cc66c40 100644
--- a/tools/perf/util/dwarf-aux.c
+++ b/tools/perf/util/dwarf-aux.c
@@ -747,14 +747,17 @@ struct __find_variable_param {
static int __die_find_variable_cb(Dwarf_Die *die_mem, void *data)
{
struct __find_variable_param *fvp = data;
+ Dwarf_Attribute attr;
int tag;

tag = dwarf_tag(die_mem);
if ((tag == DW_TAG_formal_parameter ||
tag == DW_TAG_variable) &&
- die_compare_name(die_mem, fvp->name))
+ die_compare_name(die_mem, fvp->name) &&
+ /* Does the DIE have location information or external instance? */
+ (dwarf_attr(die_mem, DW_AT_external, &attr) ||
+ dwarf_attr(die_mem, DW_AT_location, &attr)))
return DIE_FIND_CB_END;
-
if (dwarf_haspc(die_mem, fvp->addr))
return DIE_FIND_CB_CONTINUE;
else