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Subject[tip:perf/core] perf callchain: Cache eh/ debug frame offset for dwarf unwind
Commit-ID:  f1f13af99a903ae873f5373e965508e0486c1c29
Gitweb: http://git.kernel.org/tip/f1f13af99a903ae873f5373e965508e0486c1c29
Author: Namhyung Kim <namhyung@kernel.org>
AuthorDate: Thu, 29 Jan 2015 17:07:21 +0900
Committer: Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Thu, 29 Jan 2015 16:20:42 -0300

perf callchain: Cache eh/debug frame offset for dwarf unwind

When libunwind tries to resolve callchains it needs to know the offset
of .eh_frame_hdr or .debug_frame to access the dso.

Since it will always return the same result for a given DSO, just cache
the result as an optimization.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1422518843-25818-41-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/util/dso.h | 1 +
tools/perf/util/unwind-libunwind.c | 31 ++++++++++++++++++++-----------
2 files changed, 21 insertions(+), 11 deletions(-)

diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
index 3782c82..ced9284 100644
--- a/tools/perf/util/dso.h
+++ b/tools/perf/util/dso.h
@@ -139,6 +139,7 @@ struct dso {
u32 status_seen;
size_t file_size;
struct list_head open_entry;
+ u64 frame_offset;
} data;

union { /* Tool specific area */
diff --git a/tools/perf/util/unwind-libunwind.c b/tools/perf/util/unwind-libunwind.c
index 6edf535..e3c40a5 100644
--- a/tools/perf/util/unwind-libunwind.c
+++ b/tools/perf/util/unwind-libunwind.c
@@ -266,14 +266,17 @@ static int read_unwind_spec_eh_frame(struct dso *dso, struct machine *machine,
u64 *fde_count)
{
int ret = -EINVAL, fd;
- u64 offset;
+ u64 offset = dso->data.frame_offset;

- fd = dso__data_fd(dso, machine);
- if (fd < 0)
- return -EINVAL;
+ if (offset == 0) {
+ fd = dso__data_fd(dso, machine);
+ if (fd < 0)
+ return -EINVAL;

- /* Check the .eh_frame section for unwinding info */
- offset = elf_section_offset(fd, ".eh_frame_hdr");
+ /* Check the .eh_frame section for unwinding info */
+ offset = elf_section_offset(fd, ".eh_frame_hdr");
+ dso->data.frame_offset = offset;
+ }

if (offset)
ret = unwind_spec_ehframe(dso, machine, offset,
@@ -287,14 +290,20 @@ static int read_unwind_spec_eh_frame(struct dso *dso, struct machine *machine,
static int read_unwind_spec_debug_frame(struct dso *dso,
struct machine *machine, u64 *offset)
{
- int fd = dso__data_fd(dso, machine);
+ int fd;
+ u64 ofs = dso->data.frame_offset;

- if (fd < 0)
- return -EINVAL;
+ if (ofs == 0) {
+ fd = dso__data_fd(dso, machine);
+ if (fd < 0)
+ return -EINVAL;

- /* Check the .debug_frame section for unwinding info */
- *offset = elf_section_offset(fd, ".debug_frame");
+ /* Check the .debug_frame section for unwinding info */
+ ofs = elf_section_offset(fd, ".debug_frame");
+ dso->data.frame_offset = ofs;
+ }

+ *offset = ofs;
if (*offset)
return 0;


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