[PATCH v4 09/15] perf report: compare symbol name for inlined frames when matching

Milian Wolff
2017-10-01T14:31:31Z

The fake symbols we create for inlined frames will represent
different functions but can use the symbol start address. This leads
to issues when different inline branches all lead to the same
function.

Before:
~~~~~
$ perf report -s sym -i perf.inlining.data --inline --stdio -g function
...
--38.86%--_start
__libc_start_main
main
|
--37.57%--std::norm<double> (inlined)
std::_Norm_helper<true>::_S_do_it<double> (inlined)
|
--36.36%--std::abs<double> (inlined)
std::__complex_abs (inlined)
|
--12.24%--std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul>::operator() (inlined)
std::__detail::__mod<unsigned long, 2147483647ul, 16807ul, 0ul> (inlined)
std::__detail::_Mod<unsigned long, 2147483647ul, 16807ul, 0ul, true, true>::__calc (inlined)
~~~~~

Note that this backtrace representation is completely bogus.
Complex abs does not call the linear congruential engine! It
is just a side-effect of a longer inlined stack being appended
to a shorter, different inlined stack, both of which originate
in the same function (main).

This patch fixes the issue:

~~~~~
$ perf report -s sym -i perf.inlining.data --inline --stdio -g function
...
--38.86%--_start
__libc_start_main
main
|
|--35.59%--std::uniform_real_distribution<double>::operator()<std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul> > (inlined)
| std::uniform_real_distribution<double>::operator()<std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul> > (inlined)
| |
| --34.37%--std::__detail::_Adaptor<std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul>, double>::operator() (inlined)
| std::generate_canonical<double, 53ul, std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul> > (inlined)
| |
| --12.24%--std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul>::operator() (inlined)
| std::__detail::__mod<unsigned long, 2147483647ul, 16807ul, 0ul> (inlined)
| std::__detail::_Mod<unsigned long, 2147483647ul, 16807ul, 0ul, true, true>::__calc (inlined)
|
--1.99%--std::norm<double> (inlined)
std::_Norm_helper<true>::_S_do_it<double> (inlined)
std::abs<double> (inlined)
std::__complex_abs (inlined)
~~~~~

Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Yao Jin <yao.jin@linux.intel.com>
Signed-off-by: Milian Wolff <milian.wolff@kdab.com>
---
tools/perf/util/callchain.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
index c6a033ba2b73..261823ae2ea4 100644
--- a/tools/perf/util/callchain.c
+++ b/tools/perf/util/callchain.c
@@ -663,11 +663,11 @@ static enum match_result match_chain(struct callchain_cursor_node *node,
struct callchain_list *cnode)
{
struct symbol *sym = node->sym;
+ enum match_result match;
u64 left, right;

if (callchain_param.key == CCKEY_SRCLINE) {
- enum match_result match = match_chain_strings(cnode->srcline,
- node->srcline);
+ match = match_chain_strings(cnode->srcline, node->srcline);

/* if no srcline is available, fallback to symbol name */
if (match == MATCH_ERROR && cnode->ms.sym && node->sym)
@@ -681,6 +681,13 @@ static enum match_result match_chain(struct callchain_cursor_node *node,
}

if (cnode->ms.sym && sym && callchain_param.key == CCKEY_FUNCTION) {
+ /* compare inlined frames based on their symbol name because
+ * different inlined frames will have the same symbol start
+ */
+ if (cnode->ms.sym->inlined || node->sym->inlined)
+ return match_chain_strings(cnode->ms.sym->name,
+ node->sym->name);
+
left = cnode->ms.sym->start;
right = sym->start;
} else {
--
2.14.2