[PATCH 1/6] perf tools: fix incorrect ordering of callchain entries

[Chris Phlipot]

The existing implementation of thread__resolve_callchain, under certain
circumstances, can assemble callchain entries in the incorrect order.

The callchain entries are resolved incorrectly for a sample when all
of the following conditions are met:

1. callchain_param.order is set to ORDER_CALLER

2. thread__resolve_callchain_sample is able to resolve callchain entries
   for the sample.

3. unwind__get_entries is also able to resolve callchain entries for the
   sample.

The fix is accomplished by reversing the order in which
thread__resolve_callchain_sample and unwind__get_entries are called
when callchain_param.order is set to ORDER_CALLER.

Unwind specific code from thread__resolve_callchain is also moved into a
new static function to improve readability of the fix.

How to Reproduce the Existing Bug:

Modifying perf script to print call trees in the opposite order or
applying the remaining patches from this series and comparing the
results output from export-to-postgtresql.py are the easiest ways
to see the bug, however it can still be seen in current builds
using perf report.

Here is how i can reproduce the bug using perf report:
$ ./perf record --call-graph=dwarf stress -c 1 -t 5

when i run this command:
$./perf report --call-graph=flat,0,0,callee

This callchain is contained in the output, which looks correct
(callee order):

                gen8_irq_handler
                handle_irq_event_percpu
                handle_irq_event
                handle_edge_irq
                handle_irq
                do_IRQ
                ret_from_intr
                __random
                rand
                0x558f2a04dded
                0x558f2a04c774
                __libc_start_main
                0x558f2a04dcd9

Now run this command using caller order:
$./perf report --call-graph=flat,0,0,caller

It is expected to see the exact reverse of the above when using caller
order (with "0x558f2a04dcd9" at the top and "gen8_irq_handler" at the
bottom) in the output, but it is nowhere to be found.

instead you see this:

                ret_from_intr
                do_IRQ
                handle_irq
                handle_edge_irq
                handle_irq_event
                handle_irq_event_percpu
                gen8_irq_handler
                0x558f2a04dcd9
                __libc_start_main
                0x558f2a04c774
                0x558f2a04dded
                rand
                __random

Notice how internally the kernel symbols are reversed and the user space
symbols are reversed, but the kernel symbols still appear above the user
space symbols.

if this patch is applied and perf script is re-run, you will see the 
expected output (with "0x558f2a04dcd9" at the top and "gen8_irq_handler"
at the bottom):

                0x558f2a04dcd9
                __libc_start_main
                0x558f2a04c774
                0x558f2a04dded
                rand
                __random
                ret_from_intr
                do_IRQ
                handle_irq
                handle_edge_irq
                handle_irq_event
                handle_irq_event_percpu
                gen8_irq_handler

Signed-off-by: Chris Phlipot <cphlipot0@xxxxxxxxx>
---
 tools/perf/util/machine.c | 56 ++++++++++++++++++++++++++++++++++-------------
 1 file changed, 41 insertions(+), 15 deletions(-)

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 2cb95bb..baec208 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -1812,8 +1812,6 @@ static int thread__resolve_callchain_sample(struct thread *thread,
 	int skip_idx = -1;
 	int first_call = 0;
 
-	callchain_cursor_reset(cursor);
-
 	if (perf_evsel__has_branch_callstack(evsel)) {
 		err = resolve_lbr_callchain_sample(thread, cursor, sample, parent,
 						   root_al, max_stack);
@@ -1924,20 +1922,12 @@ static int unwind_entry(struct unwind_entry *entry, void *arg)
 				       entry->map, entry->sym);
 }
 
-int thread__resolve_callchain(struct thread *thread,
-			      struct callchain_cursor *cursor,
-			      struct perf_evsel *evsel,
-			      struct perf_sample *sample,
-			      struct symbol **parent,
-			      struct addr_location *root_al,
-			      int max_stack)
+static int thread__resolve_callchain_unwind(struct thread *thread,
+					    struct callchain_cursor *cursor,
+					    struct perf_evsel *evsel,
+					    struct perf_sample *sample,
+					    int max_stack)
 {
-	int ret = thread__resolve_callchain_sample(thread, cursor, evsel,
-						   sample, parent,
-						   root_al, max_stack);
-	if (ret)
-		return ret;
-
 	/* Can we do dwarf post unwind? */
 	if (!((evsel->attr.sample_type & PERF_SAMPLE_REGS_USER) &&
 	      (evsel->attr.sample_type & PERF_SAMPLE_STACK_USER)))
@@ -1950,7 +1940,43 @@ int thread__resolve_callchain(struct thread *thread,
 
 	return unwind__get_entries(unwind_entry, cursor,
 				   thread, sample, max_stack);
+}
 
+int thread__resolve_callchain(struct thread *thread,
+			      struct callchain_cursor *cursor,
+			      struct perf_evsel *evsel,
+			      struct perf_sample *sample,
+			      struct symbol **parent,
+			      struct addr_location *root_al,
+			      int max_stack)
+{
+	int ret = 0;
+
+	callchain_cursor_reset(&callchain_cursor);
+
+	if (callchain_param.order == ORDER_CALLEE) {
+		ret = thread__resolve_callchain_sample(thread, cursor,
+						       evsel, sample,
+						       parent, root_al,
+						       max_stack);
+		if (ret)
+			return ret;
+		ret = thread__resolve_callchain_unwind(thread, cursor,
+						       evsel, sample,
+						       max_stack);
+	} else {
+		ret = thread__resolve_callchain_unwind(thread, cursor,
+						       evsel, sample,
+						       max_stack);
+		if (ret)
+			return ret;
+		ret = thread__resolve_callchain_sample(thread, cursor,
+						       evsel, sample,
+						       parent, root_al,
+						       max_stack);
+	}
+
+	return ret;
 }
 
 int machine__for_each_thread(struct machine *machine,
-- 
2.7.4