selftests/bpf: Teach test_progs to cd into subdir

We are building a bunch of "flavors" of test_progs, e.g., w/ alu32 flag
for Clang when building BPF object. test_progs setup is relying on
having all the BPF object files and extra resources to be available in
current working directory, though. But we actually build all these files
into a separate sub-directory. Next set of patches establishes
convention of naming "flavored" test_progs (and test runner binaries in
general) as test_progs-flavor (e.g., test_progs-alu32), for each such
extra flavor. This patch teaches test_progs binary to automatically
detect its own extra flavor based on its argv[0], and if present, to
change current directory to a flavor-specific subdirectory.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191016060051.2024182-2-andriin@fb.com

tools/testing/selftests/bpf/test_progs.c

@@ -306,7 +306,7 @@ void *spin_lock_thread(void *arg)
 }
 
 /* extern declarations for test funcs */
-#define DEFINE_TEST(name) extern void test_##name();
+#define DEFINE_TEST(name) extern void test_##name(void);
 #include <prog_tests/tests.h>
 #undef DEFINE_TEST
 
@@ -518,6 +518,33 @@ static void stdio_restore(void)
 #endif
 }
 
+/*
+ * Determine if test_progs is running as a "flavored" test runner and switch
+ * into corresponding sub-directory to load correct BPF objects.
+ *
+ * This is done by looking at executable name. If it contains "-flavor"
+ * suffix, then we are running as a flavored test runner.
+ */
+int cd_flavor_subdir(const char *exec_name)
+{
+	/* General form of argv[0] passed here is:
+	 * some/path/to/test_progs[-flavor], where -flavor part is optional.
+	 * First cut out "test_progs[-flavor]" part, then extract "flavor"
+	 * part, if it's there.
+	 */
+	const char *flavor = strrchr(exec_name, '/');
+
+	if (!flavor)
+		return 0;
+	flavor++;
+	flavor = strrchr(flavor, '-');
+	if (!flavor)
+		return 0;
+	flavor++;
+	printf("Switching to flavor '%s' subdirectory...\n", flavor);
+	return chdir(flavor);
+}
+
 int main(int argc, char **argv)
 {
 	static const struct argp argp = {
@@ -531,6 +558,10 @@ int main(int argc, char **argv)
 	if (err)
 		return err;
 
+	err = cd_flavor_subdir(argv[0]);
+	if (err)
+		return err;
+
 	libbpf_set_print(libbpf_print_fn);
 
 	srand(time(NULL));