selftests/bpf: Support multiple tests per file

Revamp how test discovery works for test_progs and allow multiple test
entries per file. Any global void function with no arguments and
serial_test_ or test_ prefix is considered a test.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211022223228.99920-3-andrii@kernel.org

tools/testing/selftests/bpf/Makefile

@@ -421,10 +421,9 @@ ifeq ($($(TRUNNER_TESTS_DIR)-tests-hdr),)
 $(TRUNNER_TESTS_DIR)-tests-hdr := y
 $(TRUNNER_TESTS_HDR): $(TRUNNER_TESTS_DIR)/*.c
 	$$(call msg,TEST-HDR,$(TRUNNER_BINARY),$$@)
-	$$(shell ( cd $(TRUNNER_TESTS_DIR);				\
-		  echo '/* Generated header, do not edit */';		\
-		  ls *.c 2> /dev/null |					\
-			sed -e 's@\([^\.]*\)\.c@DEFINE_TEST(\1)@';	\
+	$$(shell (echo '/* Generated header, do not edit */';					\
+		  sed -n -E 's/^void (serial_)?test_([a-zA-Z0-9_]+)\((void)?\).*/DEFINE_TEST(\2)/p'	\
+			$(TRUNNER_TESTS_DIR)/*.c | sort ;	\
 		 ) > $$@)
 endif