perf tools powerpc: Adjust callchain based on DWARF debug info
When saving the callchain on Power, the kernel conservatively saves excess
entries in the callchain. A few of these entries are needed in some cases
but not others. We should use the DWARF debug information to determine
when the entries are needed.
Eg: the value in the link register (LR) is needed only when it holds the
return address of a function. At other times it must be ignored.
If the unnecessary entries are not ignored, we end up with duplicate arcs
in the call-graphs.
Use the DWARF debug information to determine if any callchain entries
should be ignored when building call-graphs.
Callgraph before the patch:
14.67% 2234 sprintft libc-2.18.so [.] __random
|
--- __random
|
|--61.12%-- __random
| |
| |--97.15%-- rand
| | do_my_sprintf
| | main
| | generic_start_main.isra.0
| | __libc_start_main
| | 0x0
| |
| --2.85%-- do_my_sprintf
| main
| generic_start_main.isra.0
| __libc_start_main
| 0x0
|
--38.88%-- rand
|
|--94.01%-- rand
| do_my_sprintf
| main
| generic_start_main.isra.0
| __libc_start_main
| 0x0
|
--5.99%-- do_my_sprintf
main
generic_start_main.isra.0
__libc_start_main
0x0
Callgraph after the patch:
14.67% 2234 sprintft libc-2.18.so [.] __random
|
--- __random
|
|--95.93%-- rand
| do_my_sprintf
| main
| generic_start_main.isra.0
| __libc_start_main
| 0x0
|
--4.07%-- do_my_sprintf
main
generic_start_main.isra.0
__libc_start_main
0x0
TODO: For split-debug info objects like glibc, we can only determine
the call-frame-address only when both .eh_frame and .debug_info
sections are available. We should be able to determin the CFA
even without the .eh_frame section.
Fix suggested by Anton Blanchard.
Thanks to valuable input on DWARF debug information from Ulrich Weigand.
Reported-by: Maynard Johnson <maynard@us.ibm.com>
Tested-by: Maynard Johnson <maynard@us.ibm.com>
Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20140625154903.GA29607@us.ibm.com
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index c73e1fc..e9b943a 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -1281,7 +1281,9 @@
u8 cpumode = PERF_RECORD_MISC_USER;
int chain_nr = min(max_stack, (int)chain->nr);
int i;
+ int j;
int err;
+ int skip_idx __maybe_unused;
callchain_cursor_reset(&callchain_cursor);
@@ -1290,14 +1292,26 @@
return 0;
}
+ /*
+ * Based on DWARF debug information, some architectures skip
+ * a callchain entry saved by the kernel.
+ */
+ skip_idx = arch_skip_callchain_idx(machine, thread, chain);
+
for (i = 0; i < chain_nr; i++) {
u64 ip;
struct addr_location al;
if (callchain_param.order == ORDER_CALLEE)
- ip = chain->ips[i];
+ j = i;
else
- ip = chain->ips[chain->nr - i - 1];
+ j = chain->nr - i - 1;
+
+#ifdef HAVE_SKIP_CALLCHAIN_IDX
+ if (j == skip_idx)
+ continue;
+#endif
+ ip = chain->ips[j];
if (ip >= PERF_CONTEXT_MAX) {
switch (ip) {