perf report: Don't crash on invalid maps in `-g srcline` mode

I just hit a segfault when doing `perf report -g srcline`.
Valgrind pointed me at this code as the culprit:

  ==8359== Invalid read of size 8
  ==8359==    at 0x3096D9: map__rip_2objdump (map.c:430)
  ==8359==    by 0x2FC1A3: match_chain_srcline (callchain.c:645)
  ==8359==    by 0x2FC1A3: match_chain (callchain.c:700)
  ==8359==    by 0x2FC1A3: append_chain (callchain.c:895)
  ==8359==    by 0x2FC1A3: append_chain_children (callchain.c:846)
  ==8359==    by 0x2FF719: callchain_append (callchain.c:944)
  ==8359==    by 0x2FF719: hist_entry__append_callchain (callchain.c:1058)
  ==8359==    by 0x32FA06: iter_add_single_cumulative_entry (hist.c:908)
  ==8359==    by 0x33195C: hist_entry_iter__add (hist.c:1050)
  ==8359==    by 0x258F65: process_sample_event (builtin-report.c:204)
  ==8359==    by 0x30D60C: perf_session__deliver_event (session.c:1310)
  ==8359==    by 0x30D60C: ordered_events__deliver_event (session.c:119)
  ==8359==    by 0x310D12: __ordered_events__flush (ordered-events.c:210)
  ==8359==    by 0x310D12: ordered_events__flush.part.3 (ordered-events.c:277)
  ==8359==    by 0x30DD3C: perf_session__process_user_event (session.c:1349)
  ==8359==    by 0x30DD3C: perf_session__process_event (session.c:1475)
  ==8359==    by 0x30FC3C: __perf_session__process_events (session.c:1867)
  ==8359==    by 0x30FC3C: perf_session__process_events (session.c:1921)
  ==8359==    by 0x25A985: __cmd_report (builtin-report.c:575)
  ==8359==    by 0x25A985: cmd_report (builtin-report.c:1054)
  ==8359==    by 0x2B9A80: run_builtin (perf.c:296)
  ==8359==  Address 0x70 is not stack'd, malloc'd or (recently) free'd

This patch fixes the issue.

Signed-off-by: Milian Wolff <milian.wolff@kdab.com>
[ Remove dependency from another change ]
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yao Jin <yao.jin@linux.intel.com>
Cc: kernel-team@lge.com
Link: http://lkml.kernel.org/r/20170524062129.32529-2-namhyung@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

tools/perf/util/callchain.c

@@ -621,14 +621,19 @@ enum match_result {
 static enum match_result match_chain_srcline(struct callchain_cursor_node *node,
 					     struct callchain_list *cnode)
 {
-	char *left = get_srcline(cnode->ms.map->dso,
+	char *left = NULL;
+	char *right = NULL;
+	enum match_result ret = MATCH_EQ;
+	int cmp;
+
+	if (cnode->ms.map)
+		left = get_srcline(cnode->ms.map->dso,
 				 map__rip_2objdump(cnode->ms.map, cnode->ip),
 				 cnode->ms.sym, true, false);
-	char *right = get_srcline(node->map->dso,
+	if (node->map)
+		right = get_srcline(node->map->dso,
 				  map__rip_2objdump(node->map, node->ip),
 				  node->sym, true, false);
-	enum match_result ret = MATCH_EQ;
-	int cmp;
 
 	if (left && right)
 		cmp = strcmp(left, right);