perf tests: Avoid raising SEGV using an obvious NULL dereference

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 <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Andi Kleen <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Stephane Eranian <[e-mail]>
Cc: Wang Nan <[e-mail]>
Link: http://lore.kernel.org/lkml/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/tests/perf-hooks.c

···
 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)