[PATCH 4/4] perf top: Show backtrace when handling a SIGSEGV on --stdio mode

[Arnaldo Carvalho de Melo]

From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

It was just freezing instead of informing about the SEGV, fix it and
also print a backtrace, just like in the TUI mode and in 'perf trace'.

Tested by provoking a NULL deref when pressing 'z':

     0.31%  libc-2.20.so     [.] malloc_consolidate
     0.31%  ld-2.20.so       [.] _dl_relocate_object
     0.28%  cc1              [.] ht_lookup
     0.28%  cc1              [.] ira_init_register_move_cost
  perf: Segmentation fault
  Obtained 7 stack frames.
  perf(dump_stack+0x32) [0x4d69f2]
  perf(sighandler_dump_stack+0x29) [0x4d6a89]
  /lib64/libc.so.6(+0x34960) [0x7f5064333960]
  perf() [0x438790]
  /lib64/libpthread.so.0(+0x752a) [0x7f50663dd52a]
  /lib64/libc.so.6(clone+0x6d) [0x7f50643ff22d]
  #

Reported-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: David Ahern <dsahern@xxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Link: http://lkml.kernel.org/n/tip-pewrpzqd29rgmhu2wkk7fhww@xxxxxxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/builtin-top.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index ecf319728f25..6135cc07213c 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -601,8 +601,8 @@ static void display_sig(int sig __maybe_unused)
 
 static void display_setup_sig(void)
 {
-	signal(SIGSEGV, display_sig);
-	signal(SIGFPE,  display_sig);
+	signal(SIGSEGV, sighandler_dump_stack);
+	signal(SIGFPE, sighandler_dump_stack);
 	signal(SIGINT,  display_sig);
 	signal(SIGQUIT, display_sig);
 	signal(SIGTERM, display_sig);
-- 
2.1.0

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