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

Masami Hiramatsu
2014-05-29T12:39:23Z

Hi Arnaldo,

Here is the patch which fixes perf probe to find variable
location correctly, on the recent dwarf format. This is not
related to the SEGV issue which I fixed in previous mail.

Thank you,

(2014/05/29 21:19), Masami Hiramatsu wrote:
> 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
>
>
>
>

--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com