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

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Message-ID: <20150313094444.GB10836@danjae.skbroadband>
Date:	Fri, 13 Mar 2015 18:44:44 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>, Li Zefan <lizefan@...wei.com>
Subject: Re: [PATCH] perf callchain: separate eh/debug frame offset cache.

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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