[PATCH 02/24] perf tests: Avoid raising SEGV using an obvious NULL dereference

[Arnaldo Carvalho de Melo]

From: Ian Rogers <irogers@xxxxxxxxxx>

An optimized build such as:

  make -C tools/perf CLANG=1 CC=clang EXTRA_CFLAGS="-O3

will turn the dereference operation into a ud2 instruction, raising a
SIGILL rather than a SIGSEGV. Use raise(..) for correctness and clarity.

Similar issues were addressed in Numfor Mbiziwo-Tiapo's patch:

  https://lkml.org/lkml/2019/7/8/1234

Committer testing:

Before:

  [root@quaco ~]# perf test hooks
  55: perf hooks                                            : Ok
  [root@quaco ~]# perf test -v hooks
  55: perf hooks                                            :
  --- start ---
  test child forked, pid 17092
  SIGSEGV is observed as expected, try to recover.
  Fatal error (SEGFAULT) in perf hook 'test'
  test child finished with 0
  ---- end ----
  perf hooks: Ok
  [root@quaco ~]#

After:

  [root@quaco ~]# perf test hooks
  55: perf hooks                                            : Ok
  [root@quaco ~]# perf test -v hooks
  55: perf hooks                                            :
  --- start ---
  test child forked, pid 17909
  SIGSEGV is observed as expected, try to recover.
  Fatal error (SEGFAULT) in perf hook 'test'
  test child finished with 0
  ---- end ----
  perf hooks: Ok
  [root@quaco ~]#

Fixes: a074865e60ed ("perf tools: Introduce perf hooks")
Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
Tested-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Cc: Wang Nan <wangnan0@xxxxxxxxxx>
Link: http://lore.kernel.org/lkml/20190925195924.152834-2-irogers@xxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/tests/perf-hooks.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/tools/perf/tests/perf-hooks.c b/tools/perf/tests/perf-hooks.c
index dbc27199c65e..dd865e0bea12 100644
--- a/tools/perf/tests/perf-hooks.c
+++ b/tools/perf/tests/perf-hooks.c
@@ -19,12 +19,11 @@ static void sigsegv_handler(int sig __maybe_unused)
 static void the_hook(void *_hook_flags)
 {
 	int *hook_flags = _hook_flags;
-	int *p = NULL;
 
 	*hook_flags = 1234;
 
 	/* Generate a segfault, test perf_hooks__recover */
-	*p = 0;
+	raise(SIGSEGV);
 }
 
 int test__perf_hooks(struct test *test __maybe_unused, int subtest __maybe_unused)
-- 
2.21.0