libbpf: Support raw BTF placed in the default search path

Currently, the default vmlinux files at '/boot/vmlinux-*',
'/lib/modules/*/vmlinux-*' etc. are parsed with 'btf__parse_elf()' to
extract BTF. It is possible that these files are actually raw BTF files
similar to /sys/kernel/btf/vmlinux. So parse these files with
'btf__parse' which tries both raw format and ELF format.

This might be useful in some scenarios where users put their custom BTF
into known locations and don't want to specify btf_custom_path option.

Signed-off-by: Tao Chen <chentao.kernel@linux.alibaba.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/3f59fb5a345d2e4f10e16fe9e35fbc4c03ecaa3e.1662999860.git.chentao.kernel@linux.alibaba.com

tools/lib/bpf/btf.c

@@ -4642,20 +4642,17 @@ static int btf_dedup_remap_types(struct btf_dedup *d)
  */
 struct btf *btf__load_vmlinux_btf(void)
 {
-	struct {
-		const char *path_fmt;
-		bool raw_btf;
-	} locations[] = {
+	const char *locations[] = {
 		/* try canonical vmlinux BTF through sysfs first */
-		{ "/sys/kernel/btf/vmlinux", true /* raw BTF */ },
-		/* fall back to trying to find vmlinux ELF on disk otherwise */
-		{ "/boot/vmlinux-%1$s" },
-		{ "/lib/modules/%1$s/vmlinux-%1$s" },
-		{ "/lib/modules/%1$s/build/vmlinux" },
-		{ "/usr/lib/modules/%1$s/kernel/vmlinux" },
-		{ "/usr/lib/debug/boot/vmlinux-%1$s" },
-		{ "/usr/lib/debug/boot/vmlinux-%1$s.debug" },
-		{ "/usr/lib/debug/lib/modules/%1$s/vmlinux" },
+		"/sys/kernel/btf/vmlinux",
+		/* fall back to trying to find vmlinux on disk otherwise */
+		"/boot/vmlinux-%1$s",
+		"/lib/modules/%1$s/vmlinux-%1$s",
+		"/lib/modules/%1$s/build/vmlinux",
+		"/usr/lib/modules/%1$s/kernel/vmlinux",
+		"/usr/lib/debug/boot/vmlinux-%1$s",
+		"/usr/lib/debug/boot/vmlinux-%1$s.debug",
+		"/usr/lib/debug/lib/modules/%1$s/vmlinux",
 	};
 	char path[PATH_MAX + 1];
 	struct utsname buf;
@@ -4665,15 +4662,12 @@ struct btf *btf__load_vmlinux_btf(void)
 	uname(&buf);
 
 	for (i = 0; i < ARRAY_SIZE(locations); i++) {
-		snprintf(path, PATH_MAX, locations[i].path_fmt, buf.release);
+		snprintf(path, PATH_MAX, locations[i], buf.release);
 
 		if (access(path, R_OK))
 			continue;
 
-		if (locations[i].raw_btf)
-			btf = btf__parse_raw(path);
-		else
-			btf = btf__parse_elf(path, NULL);
+		btf = btf__parse(path, NULL);
 		err = libbpf_get_error(btf);
 		pr_debug("loading kernel BTF '%s': %d\n", path, err);
 		if (err)