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perf tools powerpc: Adjust callchain based on DWARF debug info

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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>
This commit is contained in:
Sukadev Bhattiprolu
2014-06-25 08:49:03 -07:00
committed by Jiri Olsa
parent 21da83fb6c
commit a60335ba32
5 changed files with 300 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

18
tools/perf/util/machine.c
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@@ -1281,7 +1281,9 @@ static int machine__resolve_callchain_sample(struct machine *machine,
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 @@ static int machine__resolve_callchain_sample(struct machine *machine,
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) {