perf tools: Introduce perf hooks

Perf hooks allow hooking user code at perf events. They can be used for
manipulation of BPF maps, taking snapshot and reporting results. In this
patch two perf hook points are introduced: record_start and record_end.

To avoid buggy user actions, a SIGSEGV signal handler is introduced into
'perf record'. It turns off perf hook if it causes a segfault and report
an error to help debugging.

A test case for perf hook is introduced.

Test result:
  $ ./buildperf/perf test -v hook
  50: Test perf hooks                                          :
  --- start ---
  test child forked, pid 10311
  SIGSEGV is observed as expected, try to recover.
  Fatal error (SEGFAULT) in perf hook 'test'
  test child finished with 0
  ---- end ----
  Test perf hooks: Ok

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Alexei Starovoitov <ast@fb.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Joe Stringer <joe@ovn.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/20161126070354.141764-5-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/Build

@@ -42,6 +42,7 @@ perf-y += backward-ring-buffer.o
 perf-y += sdt.o
 perf-y += is_printable_array.o
 perf-y += bitmap.o
+perf-y += perf-hooks.o
 
 $(OUTPUT)tests/llvm-src-base.c: tests/bpf-script-example.c tests/Build
 	$(call rule_mkdir)

tools/perf/tests/builtin-test.c

@@ -229,6 +229,10 @@ static struct test generic_tests[] = {
 		.desc = "Test bitmap print",
 		.func = test__bitmap_print,
 	},
+	{
+		.desc = "Test perf hooks",
+		.func = test__perf_hooks,
+	},
 	{
 		.func = NULL,
 	},

tools/perf/tests/perf-hooks.c

@@ -0,0 +1,44 @@
+#include <signal.h>
+#include <stdlib.h>
+
+#include "tests.h"
+#include "debug.h"
+#include "util.h"
+#include "perf-hooks.h"
+
+static void sigsegv_handler(int sig __maybe_unused)
+{
+	pr_debug("SIGSEGV is observed as expected, try to recover.\n");
+	perf_hooks__recover();
+	signal(SIGSEGV, SIG_DFL);
+	raise(SIGSEGV);
+	exit(-1);
+}
+
+static int hook_flags;
+
+static void the_hook(void)
+{
+	int *p = NULL;
+
+	hook_flags = 1234;
+
+	/* Generate a segfault, test perf_hooks__recover */
+	*p = 0;
+}
+
+int test__perf_hooks(int subtest __maybe_unused)
+{
+	signal(SIGSEGV, sigsegv_handler);
+	perf_hooks__set_hook("test", the_hook);
+	perf_hooks__invoke_test();
+
+	/* hook is triggered? */
+	if (hook_flags != 1234)
+		return TEST_FAIL;
+
+	/* the buggy hook is removed? */
+	if (perf_hooks__get_hook("test"))
+		return TEST_FAIL;
+	return TEST_OK;
+}

tools/perf/tests/tests.h

@@ -91,6 +91,7 @@ int test__cpu_map_print(int subtest);
 int test__sdt_event(int subtest);
 int test__is_printable_array(int subtest);
 int test__bitmap_print(int subtest);
+int test__perf_hooks(int subtest);
 
 #if defined(__arm__) || defined(__aarch64__)
 #ifdef HAVE_DWARF_UNWIND_SUPPORT