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Commit f08046cb authored by Adrian Hunter's avatar Adrian Hunter Committed by Arnaldo Carvalho de Melo
Browse files

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 <main>:
      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: default avatarAdrian Hunter <adrian.hunter@intel.com>
Tested-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: default avatarJiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/20190109091835.5570-5-adrian.hunter@intel.com


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent 90c2cda7

tools/perf/scripts/python/export-to-postgresql.py

+1 −1
Original line number Diff line number Diff line
@@ -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')

tools/perf/scripts/python/export-to-sqlite.py

+1 −1
Original line number Diff line number Diff line
@@ -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')

tools/perf/util/thread-stack.c

+28 −2
Original line number Diff line number Diff line
@@ -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;

tools/perf/util/thread-stack.h

+3 −0
Original line number Diff line number Diff line
@@ -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,

};



/**