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perf thread-stack: Represent jmps to the start of a different symbol
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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: 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>
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@ahunter6 @acmel
ahunter6 authored and acmel committed Feb 6, 2019
1 parent 90c2cda commit f08046c
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Showing 4 changed files with 33 additions and 4 deletions.
2 changes: 1 addition & 1 deletion tools/perf/scripts/python/export-to-postgresql.py
View file
Original file line number Diff line number Diff line change
Expand Up @@ -478,7 +478,7 @@ def do_query(q, s):
'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')

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2 changes: 1 addition & 1 deletion tools/perf/scripts/python/export-to-sqlite.py
View file
Original file line number Diff line number Diff line change
Expand Up @@ -320,7 +320,7 @@ def emit_to_hex(x):
'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')

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30 changes: 28 additions & 2 deletions tools/perf/util/thread-stack.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand All @@ -47,6 +48,7 @@ struct thread_stack_entry {
struct call_path *cp;
bool no_call;
bool trace_end;
bool non_call;
};

/**
Expand Down Expand Up @@ -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);
}
Expand Down Expand Up @@ -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;
}
Expand All @@ -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) {
Expand Down Expand Up @@ -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;
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3 changes: 3 additions & 0 deletions tools/perf/util/thread-stack.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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,
};

/**
Expand Down

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