[tip:perf/core] perf thread-stack: Represent jmps to the start of a different symbol

tip-bot for Adrian Hunter
2019-02-09T12:59:44Z

Commit-ID: f08046cb3082b313e7b08dc35838cf8bd902c36b
Gitweb: https://git.kernel.org/tip/f08046cb3082b313e7b08dc35838cf8bd902c36b
Author: Adrian Hunter <adrian.hunter@intel.com>
AuthorDate: Wed, 9 Jan 2019 11:18:33 +0200
Committer: Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Wed, 6 Feb 2019 10:00:40 -0300

perf thread-stack: Represent jmps to the start of a different symbol

The compiler might optimize a call/ret combination by making it a jmp.
However the thread-stack does not presently cater for that, so that such
control flow is not visible in the call graph. Make it visible by
recording on the stack a branch to the start of a different symbol.
Note, that means when a ret pops the stack, all jmps must be popped off
first.

Example:

$ cat jmp-to-fn.c
__attribute__((noinline)) int bar(void)
{
return -1;
}

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

int main()
{
return foo();
}
$ gcc -ggdb3 -Wall -Wextra -O2 -o jmp-to-fn jmp-to-fn.c
$ objdump -d jmp-to-fn
<SNIP>
0000000000001040 :
1040: 31 c0 xor %eax,%eax
1042: e9 09 01 00 00 jmpq 1150 <foo>
<SNIP>
0000000000001140 <bar>:
1140: b8 ff ff ff ff mov $0xffffffff,%eax
1145: c3 retq
<SNIP>
0000000000001150 <foo>:
1150: 31 c0 xor %eax,%eax
1152: e8 e9 ff ff ff callq 1140 <bar>
1157: 83 c0 01 add $0x1,%eax
115a: c3 retq
<SNIP>
$ perf record -o jmp-to-fn.perf.data -e intel_pt/cyc/u ./jmp-to-fn
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0,017 MB jmp-to-fn.perf.data ]
$ perf script -i jmp-to-fn.perf.data --itrace=be -s ~/libexec/perf-core/scripts/python/export-to-sqlite.py jmp-to-fn.db branches calls
2019-01-08 13:24:58.783069 Creating database...
2019-01-08 13:24:58.794650 Writing records...
2019-01-08 13:24:59.008050 Adding indexes
2019-01-08 13:24:59.015802 Done
$ ~/libexec/perf-core/scripts/python/exported-sql-viewer.py jmp-to-fn.db

Before:

main
-> bar

After:

main
-> foo
-> bar

Committer testing:

Install the python2-pyside package, then select these menu options
on the GUI:

"Reports"
"Context sensitive callgraphs"

Then go on expanding the symbols, to get, full picture when doing this
on a fedora:29 with gcc version 8.2.1 20181215 (Red Hat 8.2.1-6) (GCC):

jmp-to-fn
PID:TID
_start (ld-2.28.so)
__libc_start_main
main
foo
bar

To verify that indeed, this fixes the problem.

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/20190109091835.5570-5-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/scripts/python/export-to-postgresql.py | 2 +-
tools/perf/scripts/python/export-to-sqlite.py | 2 +-
tools/perf/util/thread-stack.c | 30 +++++++++++++++++++++--
tools/perf/util/thread-stack.h | 3 +++
4 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/tools/perf/scripts/python/export-to-postgresql.py b/tools/perf/scripts/python/export-to-postgresql.py
index 0564dd7377f2..30130213da7e 100644
--- a/tools/perf/scripts/python/export-to-postgresql.py
+++ b/tools/perf/scripts/python/export-to-postgresql.py
@@ -478,7 +478,7 @@ if perf_db_export_calls:
'branch_count,'
'call_id,'
'return_id,'
- 'CASE WHEN flags=1 THEN \'no call\' WHEN flags=2 THEN \'no return\' WHEN flags=3 THEN \'no call/return\' ELSE \'\' END AS flags,'
+ 'CASE WHEN flags=0 THEN \'\' WHEN flags=1 THEN \'no call\' WHEN flags=2 THEN \'no return\' WHEN flags=3 THEN \'no call/return\' WHEN flags=6 THEN \'jump\' ELSE flags END AS flags,'
'parent_call_path_id'
' FROM calls INNER JOIN call_paths ON call_paths.id = call_path_id')

diff --git a/tools/perf/scripts/python/export-to-sqlite.py b/tools/perf/scripts/python/export-to-sqlite.py
index 245caf2643ed..ed237f2ed03f 100644
--- a/tools/perf/scripts/python/export-to-sqlite.py
+++ b/tools/perf/scripts/python/export-to-sqlite.py
@@ -320,7 +320,7 @@ if perf_db_export_calls:
'branch_count,'
'call_id,'
'return_id,'
- 'CASE WHEN flags=1 THEN \'no call\' WHEN flags=2 THEN \'no return\' WHEN flags=3 THEN \'no call/return\' ELSE \'\' END AS flags,'
+ 'CASE WHEN flags=0 THEN \'\' WHEN flags=1 THEN \'no call\' WHEN flags=2 THEN \'no return\' WHEN flags=3 THEN \'no call/return\' WHEN flags=6 THEN \'jump\' ELSE flags END AS flags,'
'parent_call_path_id'
' FROM calls INNER JOIN call_paths ON call_paths.id = call_path_id')

diff --git a/tools/perf/util/thread-stack.c b/tools/perf/util/thread-stack.c
index 7f8eff018c16..f52c0f90915d 100644
--- a/tools/perf/util/thread-stack.c
+++ b/tools/perf/util/thread-stack.c
@@ -38,6 +38,7 @@
* @cp: call path
* @no_call: a 'call' was not seen
* @trace_end: a 'call' but trace ended
+ * @non_call: a branch but not a 'call' to the start of a different symbol
*/
struct thread_stack_entry {
u64 ret_addr;
@@ -47,6 +48,7 @@ struct thread_stack_entry {
struct call_path *cp;
bool no_call;
bool trace_end;
+ bool non_call;
};

/**
@@ -268,6 +270,8 @@ static int thread_stack__call_return(struct thread *thread,
cr.flags |= CALL_RETURN_NO_CALL;
if (no_return)
cr.flags |= CALL_RETURN_NO_RETURN;
+ if (tse->non_call)
+ cr.flags |= CALL_RETURN_NON_CALL;

return crp->process(&cr, crp->data);
}
@@ -510,6 +514,7 @@ static int thread_stack__push_cp(struct thread_stack *ts, u64 ret_addr,
tse->cp = cp;
tse->no_call = no_call;
tse->trace_end = trace_end;
+ tse->non_call = false;

return 0;
}
@@ -531,14 +536,16 @@ static int thread_stack__pop_cp(struct thread *thread, struct thread_stack *ts,
timestamp, ref, false);
}

- if (ts->stack[ts->cnt - 1].ret_addr == ret_addr) {
+ if (ts->stack[ts->cnt - 1].ret_addr == ret_addr &&
+ !ts->stack[ts->cnt - 1].non_call) {
return thread_stack__call_return(thread, ts, --ts->cnt,
timestamp, ref, false);
} else {
size_t i = ts->cnt - 1;

while (i--) {
- if (ts->stack[i].ret_addr != ret_addr)
+ if (ts->stack[i].ret_addr != ret_addr ||
+ ts->stack[i].non_call)
continue;
i += 1;
while (ts->cnt > i) {
@@ -757,6 +764,25 @@ int thread_stack__process(struct thread *thread, struct comm *comm,
err = thread_stack__trace_begin(thread, ts, sample->time, ref);
} else if (sample->flags & PERF_IP_FLAG_TRACE_END) {
err = thread_stack__trace_end(ts, sample, ref);
+ } else if (sample->flags & PERF_IP_FLAG_BRANCH &&
+ from_al->sym != to_al->sym && to_al->sym &&
+ to_al->addr == to_al->sym->start) {
+ struct call_path_root *cpr = ts->crp->cpr;
+ struct call_path *cp;
+
+ /*
+ * The compiler might optimize a call/ret combination by making
+ * it a jmp. Make that visible by recording on the stack a
+ * branch to the start of a different symbol. Note, that means
+ * when a ret pops the stack, all jmps must be popped off first.
+ */
+ cp = call_path__findnew(cpr, ts->stack[ts->cnt - 1].cp,
+ to_al->sym, sample->addr,
+ ts->kernel_start);
+ err = thread_stack__push_cp(ts, 0, sample->time, ref, cp, false,
+ false);
+ if (!err)
+ ts->stack[ts->cnt - 1].non_call = true;
}

return err;
diff --git a/tools/perf/util/thread-stack.h b/tools/perf/util/thread-stack.h
index 1f626f4a1c40..b7c04e19ad41 100644
--- a/tools/perf/util/thread-stack.h
+++ b/tools/perf/util/thread-stack.h
@@ -35,10 +35,13 @@ struct call_path;
*
* CALL_RETURN_NO_CALL: 'return' but no matching 'call'
* CALL_RETURN_NO_RETURN: 'call' but no matching 'return'
+ * CALL_RETURN_NON_CALL: a branch but not a 'call' to the start of a different
+ * symbol
*/
enum {
CALL_RETURN_NO_CALL = 1 << 0,
CALL_RETURN_NO_RETURN = 1 << 1,
+ CALL_RETURN_NON_CALL = 1 << 2,
};

/**