[PATCH] perf hists browser: Fix segfault if use symbol filter in cmdline

[Wang Nan]

If feed perf a symbol filter in cmdline and the result is empty,
pressing 'Enter' in the hist browser causes crash:

 # ./perf report perf.data   <-- Common mistake for beginners

Then press 'Enter':

 perf: Segmentation fault
 -------- backtrace --------
 /home/wangnan/perf[0x53e578]
 /lib64/libc.so.6(+0x3545f)[0x7f76bafe045f]
 /home/wangnan/perf[0x539dd4]
 /home/wangnan/perf(perf_evlist__tui_browse_hists+0x96)[0x53d216]
 /home/wangnan/perf(cmd_report+0x1b9f)[0x442c7f]
 /home/wangnan/perf[0x47efa2]
 /home/wangnan/perf(main+0x5f5)[0x432fa5]
 /lib64/libc.so.6(__libc_start_main+0xf4)[0x7f76bafccbd4]
 /home/wangnan/perf[0x4330d4]

This is because 'perf.data' is interperted as a symbol filter, and the
result is empty, so selection is empty. However,
hist_browser__toggle_fold() forgets to check it.

This patch simply return faluse when selection is NULL.

Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
---
 tools/perf/ui/browsers/hists.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/perf/ui/browsers/hists.c b/tools/perf/ui/browsers/hists.c
index dcdcbaf..33da341 100644
--- a/tools/perf/ui/browsers/hists.c
+++ b/tools/perf/ui/browsers/hists.c
@@ -337,9 +337,12 @@ static bool hist_browser__toggle_fold(struct hist_browser *browser)
 {
 	struct hist_entry *he = browser->he_selection;
 	struct map_symbol *ms = browser->selection;
-	struct callchain_list *cl = container_of(ms, struct callchain_list, ms);
+	struct callchain_list *cl = ms ? container_of(ms, struct callchain_list, ms) : NULL;
 	bool has_children;
 
+	if (!ms)
+		return false;
+
 	if (ms == &he->ms)
 		has_children = hist_entry__toggle_fold(he);
 	else
-- 
1.8.3.4

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