[tip:perf/core] perf thread-stack: Improve thread_stack__no_call_return()

tip-bot for Adrian Hunter
2019-02-28T07:49:26Z

Commit-ID: 1f35cd65386e02430546727bd3cc2508d052e3ec
Gitweb: https://git.kernel.org/tip/1f35cd65386e02430546727bd3cc2508d052e3ec
Author: Adrian Hunter <adrian.hunter@intel.com>
AuthorDate: Wed, 9 Jan 2019 11:18:34 +0200
Committer: Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Fri, 22 Feb 2019 11:42:34 -0300

perf thread-stack: Improve thread_stack__no_call_return()

Improve thread_stack__no_call_return() to better handle 'returns' that
do not match the stack i.e. 'no call'. See code comments for details.
The example below shows how retpolines are affected:

Example:

$ cat simple-retpoline.c
__attribute__((noinline)) int bar(void)
{
return -1;
}

int foo(void)
{
return bar() + 1;
}

__attribute__((indirect_branch("thunk"))) int main()
{
int (*volatile fn)(void) = foo;

fn();
return fn();
}
$ gcc -ggdb3 -Wall -Wextra -O2 -o simple-retpoline simple-retpoline.c
$ objdump -d simple-retpoline
<SNIP>
0000000000001040 :
1040: 48 83 ec 18 sub $0x18,%rsp
1044: 48 8d 05 25 01 00 00 lea 0x125(%rip),%rax # 1170 <foo>
104b: 48 89 44 24 08 mov %rax,0x8(%rsp)
1050: 48 8b 44 24 08 mov 0x8(%rsp),%rax
1055: e8 1f 01 00 00 callq 1179 <__x86_indirect_thunk_rax>
105a: 48 8b 44 24 08 mov 0x8(%rsp),%rax
105f: 48 83 c4 18 add $0x18,%rsp
1063: e9 11 01 00 00 jmpq 1179 <__x86_indirect_thunk_rax>
<SNIP>
0000000000001160 <bar>:
1160: b8 ff ff ff ff mov $0xffffffff,%eax
1165: c3 retq
<SNIP>
0000000000001170 <foo>:
1170: e8 eb ff ff ff callq 1160 <bar>
1175: 83 c0 01 add $0x1,%eax
1178: c3 retq
0000000000001179 <__x86_indirect_thunk_rax>:
1179: e8 07 00 00 00 callq 1185 <__x86_indirect_thunk_rax+0xc>
117e: f3 90 pause
1180: 0f ae e8 lfence
1183: eb f9 jmp 117e <__x86_indirect_thunk_rax+0x5>
1185: 48 89 04 24 mov %rax,(%rsp)
1189: c3 retq
<SNIP>
$ perf record -o simple-retpoline.perf.data -e intel_pt/cyc/u ./simple-retpoline
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0,017 MB simple-retpoline.perf.data ]
$ perf script -i simple-retpoline.perf.data --itrace=be -s ~/libexec/perf-core/scripts/python/export-to-sqlite.py simple-retpoline.db branches calls
2019-01-08 14:03:37.851655 Creating database...
2019-01-08 14:03:37.863256 Writing records...
2019-01-08 14:03:38.069750 Adding indexes
2019-01-08 14:03:38.078799 Done
$ ~/libexec/perf-core/scripts/python/exported-sql-viewer.py simple-retpoline.db

Before:

main
-> __x86_indirect_thunk_rax
-> __x86_indirect_thunk_rax
-> __x86_indirect_thunk_rax
-> bar

After:

main
-> __x86_indirect_thunk_rax
-> __x86_indirect_thunk_rax
-> foo
-> bar

Committer testing:

Chose "Reports", Then "Context-Sensitive Call Graph" and then go on
expanding:

Before:

simple-retpolin
PID:PID
_start
_start
__libc_start_main
main
__x86_indirect_thunk_rax
__x86_indirect_thunk_rax
bar

After:

Remove the "simple.retpoline.db" file, run again the 'perf script' line
to regenerate the .db file and run the exported-sql-viewer.py again to
get the same all the way to 'main', then, from there, including 'main':

main
__x86_indirect_thunk_rax
__x86_indirect_thunk_rax
foo
bar

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/20190109091835.5570-6-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/util/thread-stack.c | 49 +++++++++++++++++++++++++++++++++++++++---
1 file changed, 46 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/thread-stack.c b/tools/perf/util/thread-stack.c
index f52c0f90915d..632c07a125ab 100644
--- a/tools/perf/util/thread-stack.c
+++ b/tools/perf/util/thread-stack.c
@@ -638,14 +638,57 @@ static int thread_stack__no_call_return(struct thread *thread,
else
parent = root;

- /* This 'return' had no 'call', so push and pop top of stack */
- cp = call_path__findnew(cpr, parent, fsym, ip, ks);
+ if (parent->sym == from_al->sym) {
+ /*
+ * At the bottom of the stack, assume the missing 'call' was
+ * before the trace started. So, pop the current symbol and push
+ * the 'to' symbol.
+ */
+ if (ts->cnt == 1) {
+ err = thread_stack__call_return(thread, ts, --ts->cnt,
+ tm, ref, false);
+ if (err)
+ return err;
+ }
+
+ if (!ts->cnt) {
+ cp = call_path__findnew(cpr, root, tsym, addr, ks);
+
+ return thread_stack__push_cp(ts, addr, tm, ref, cp,
+ true, false);
+ }
+
+ /*
+ * Otherwise assume the 'return' is being used as a jump (e.g.
+ * retpoline) and just push the 'to' symbol.
+ */
+ cp = call_path__findnew(cpr, parent, tsym, addr, ks);
+
+ err = thread_stack__push_cp(ts, 0, tm, ref, cp, true, false);
+ if (!err)
+ ts->stack[ts->cnt - 1].non_call = true;
+
+ return err;
+ }
+
+ /*
+ * Assume 'parent' has not yet returned, so push 'to', and then push and
+ * pop 'from'.
+ */
+
+ cp = call_path__findnew(cpr, parent, tsym, addr, ks);

err = thread_stack__push_cp(ts, addr, tm, ref, cp, true, false);
if (err)
return err;

- return thread_stack__pop_cp(thread, ts, addr, tm, ref, tsym);
+ cp = call_path__findnew(cpr, cp, fsym, ip, ks);
+
+ err = thread_stack__push_cp(ts, ip, tm, ref, cp, true, false);
+ if (err)
+ return err;
+
+ return thread_stack__call_return(thread, ts, --ts->cnt, tm, ref, false);
}

static int thread_stack__trace_begin(struct thread *thread,