linux-kernel - Re: [PATCH] perf callchain: separate eh/debug frame offset cache.

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Date:	Thu, 19 Mar 2015 14:20:16 +0800
From:	Wang Nan <wangnan0@...wei.com>
To:	Ingo Molnar <mingo@...hat.com>
CC:	Namhyung Kim <namhyung@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Li Zefan <lizefan@...wei.com>
Subject: Re: [PATCH] perf callchain: separate eh/debug frame offset cache.

Hi Ingo,

Could you please collect this patch? It fixes a bug which prevent unwind for ARM.

Thank you.

On 2015/3/13 17:44, Namhyung Kim wrote:
> Hi Wang,
> 
> On Fri, Mar 13, 2015 at 03:02:56PM +0800, Wang Nan wrote:
>> Commit f1f13af99a90 ("perf callchain: Cache eh/debug frame offset for
>> dwarf unwind") introduces a cache for .debug_frame and .eh_frame_hdr.
>> Unfortunately, it makes them share a same cache (dso->frame_offset).
>> Which causes unwind failure on ARM:
>>
>>    $ perf test unwind
>>   Test dwarf unwind: FAILED!
>>
>> The reason is that, if a dso has '.debug_frame' but doesn't have
>> '.eh_frame_hdr' (like ARM), dso->frame_offset will be filled by offset
>> of '.debug_frame' during the first time calling of find_proc_info() ->
>> read_unwind_spec_debug_frame(), and be regarded to '.eh_frame_hdr' when
>> the second time calling of find_proc_info() ->
>> read_unwind_spec_eh_frame(), since '.eh_frame_hdr' is checked prior to
>> '.debug_frame'.
>>
>> This patch solves the problem by creating two cache fields for
>> '.eh_frame_hdr' and '.debug_frame'.
>>
>> Signed-off-by: Wang Nan <wangnan0@...wei.com>
> 
> Acked-by: Namhyung Kim <namhyung@...nel.org>
> 
> Thanks,
> Namhyung
> 
> 
>> ---
>>  tools/perf/util/dso.h              | 3 ++-
>>  tools/perf/util/unwind-libunwind.c | 8 ++++----
>>  2 files changed, 6 insertions(+), 5 deletions(-)
>>
>> diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
>> index ced9284..408c65f 100644
>> --- a/tools/perf/util/dso.h
>> +++ b/tools/perf/util/dso.h
>> @@ -139,7 +139,8 @@ struct dso {
>>  		u32		 status_seen;
>>  		size_t		 file_size;
>>  		struct list_head open_entry;
>> -		u64		 frame_offset;
>> +		u64		 debug_frame_offset;
>> +		u64		 eh_frame_hdr_offset;
>>  	} data;
>>
>>  	union { /* Tool specific area */
>> diff --git a/tools/perf/util/unwind-libunwind.c b/tools/perf/util/unwind-libunwind.c
>> index e3c40a5..7b09a44 100644
>> --- a/tools/perf/util/unwind-libunwind.c
>> +++ b/tools/perf/util/unwind-libunwind.c
>> @@ -266,7 +266,7 @@ static int read_unwind_spec_eh_frame(struct dso *dso, struct machine *machine,
>>  				     u64 *fde_count)
>>  {
>>  	int ret = -EINVAL, fd;
>> -	u64 offset = dso->data.frame_offset;
>> +	u64 offset = dso->data.eh_frame_hdr_offset;
>>
>>  	if (offset == 0) {
>>  		fd = dso__data_fd(dso, machine);
>> @@ -275,7 +275,7 @@ static int read_unwind_spec_eh_frame(struct dso *dso, struct machine *machine,
>>
>>  		/* Check the .eh_frame section for unwinding info */
>>  		offset = elf_section_offset(fd, ".eh_frame_hdr");
>> -		dso->data.frame_offset = offset;
>> +		dso->data.eh_frame_hdr_offset = offset;
>>  	}
>>
>>  	if (offset)
>> @@ -291,7 +291,7 @@ static int read_unwind_spec_debug_frame(struct dso *dso,
>>  					struct machine *machine, u64 *offset)
>>  {
>>  	int fd;
>> -	u64 ofs = dso->data.frame_offset;
>> +	u64 ofs = dso->data.debug_frame_offset;
>>
>>  	if (ofs == 0) {
>>  		fd = dso__data_fd(dso, machine);
>> @@ -300,7 +300,7 @@ static int read_unwind_spec_debug_frame(struct dso *dso,
>>
>>  		/* Check the .debug_frame section for unwinding info */
>>  		ofs = elf_section_offset(fd, ".debug_frame");
>> -		dso->data.frame_offset = ofs;
>> +		dso->data.debug_frame_offset = ofs;
>>  	}
>>
>>  	*offset = ofs;
>> --
>> 1.8.3.4
>>


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