selftests/bpf: Rename progs/tag.c to progs/btf_decl_tag.c

Rename progs/tag.c to progs/btf_decl_tag.c so we can introduce
progs/btf_type_tag.c in the next patch.

Also create a subtest for btf_decl_tag in prog_tests/btf_tag.c
so we can introduce btf_type_tag subtest in the next patch.

I also took opportunity to remove the check whether __has_attribute
is defined or not in progs/btf_decl_tag.c since all recent
clangs should already support this macro.
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211112012641.1507144-1-yhs@fb.com

tools/testing/selftests/bpf/prog_tests/btf_tag.c

 // SPDX-License-Identifier: GPL-2.0
 /* Copyright (c) 2021 Facebook */
 #include <test_progs.h>
-#include "tag.skel.h"
+#include "btf_decl_tag.skel.h"
 
-void test_btf_tag(void)
+static void test_btf_decl_tag(void)
 {
-	struct tag *skel;
+	struct btf_decl_tag *skel;
 
-	skel = tag__open_and_load();
-	if (!ASSERT_OK_PTR(skel, "btf_tag"))
+	skel = btf_decl_tag__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "btf_decl_tag"))
 		return;
 
 	if (skel->rodata->skip_tests) {
-		printf("%s:SKIP: btf_tag attribute not supported", __func__);
+		printf("%s:SKIP: btf_decl_tag attribute not supported", __func__);
 		test__skip();
 	}
 
-	tag__destroy(skel);
+	btf_decl_tag__destroy(skel);
+}
+
+void test_btf_tag(void)
+{
+	if (test__start_subtest("btf_decl_tag"))
+		test_btf_decl_tag();
 }

tools/testing/selftests/bpf/progs/tag.c → tools/testing/selftests/bpf/progs/btf_decl_tag.c

@@ -4,10 +4,6 @@
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 
-#ifndef __has_attribute
-#define __has_attribute(x) 0
-#endif
-
 #if __has_attribute(btf_decl_tag)
 #define __tag1 __attribute__((btf_decl_tag("tag1")))
 #define __tag2 __attribute__((btf_decl_tag("tag2")))