perf tools: Auto detecting kernel build directory

This patch detects kernel build directory by checking the existence of
include/generated/autoconf.h.

clang working directory is changed to kbuild directory if it is found,
to help user use relative include path. Following patch will detect
kernel include directory, which contains relative include patch so this
workdir changing is needed.

Users are allowed to set 'kbuild-dir = ""' manually to disable this
checking.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David Ahern <dsahern@gmail.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kaixu Xia <xiakaixu@huawei.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/n/tip-owyfwfbemrjn0tlj6tgk2nf5@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/llvm-utils.c

@@ -4,6 +4,7 @@
  */
 
 #include <stdio.h>
+#include <sys/utsname.h>
 #include "util.h"
 #include "debug.h"
 #include "llvm-utils.h"
@@ -204,6 +205,74 @@ version_notice(void)
 );
 }
 
+static int detect_kbuild_dir(char **kbuild_dir)
+{
+	const char *test_dir = llvm_param.kbuild_dir;
+	const char *prefix_dir = "";
+	const char *suffix_dir = "";
+
+	char *autoconf_path;
+	struct utsname utsname;
+
+	int err;
+
+	if (!test_dir) {
+		err = uname(&utsname);
+		if (err) {
+			pr_warning("uname failed: %s\n", strerror(errno));
+			return -EINVAL;
+		}
+
+		test_dir = utsname.release;
+		prefix_dir = "/lib/modules/";
+		suffix_dir = "/build";
+	}
+
+	err = asprintf(&autoconf_path, "%s%s%s/include/generated/autoconf.h",
+		       prefix_dir, test_dir, suffix_dir);
+	if (err < 0)
+		return -ENOMEM;
+
+	if (access(autoconf_path, R_OK) == 0) {
+		free(autoconf_path);
+
+		err = asprintf(kbuild_dir, "%s%s%s", prefix_dir, test_dir,
+			       suffix_dir);
+		if (err < 0)
+			return -ENOMEM;
+		return 0;
+	}
+	free(autoconf_path);
+	return -ENOENT;
+}
+
+static inline void
+get_kbuild_opts(char **kbuild_dir)
+{
+	int err;
+
+	if (!kbuild_dir)
+		return;
+
+	*kbuild_dir = NULL;
+
+	if (llvm_param.kbuild_dir && !llvm_param.kbuild_dir[0]) {
+		pr_debug("[llvm.kbuild-dir] is set to \"\" deliberately.\n");
+		pr_debug("Skip kbuild options detection.\n");
+		return;
+	}
+
+	err = detect_kbuild_dir(kbuild_dir);
+	if (err) {
+		pr_warning(
+"WARNING:\tunable to get correct kernel building directory.\n"
+"Hint:\tSet correct kbuild directory using 'kbuild-dir' option in [llvm]\n"
+"     \tsection of ~/.perfconfig or set it to \"\" to suppress kbuild\n"
+"     \tdetection.\n\n");
+		return;
+	}
+}
+
 int llvm__compile_bpf(const char *path, void **p_obj_buf,
 		      size_t *p_obj_buf_sz)
 {
@@ -211,6 +280,7 @@ int llvm__compile_bpf(const char *path, void **p_obj_buf,
 	char clang_path[PATH_MAX];
 	const char *clang_opt = llvm_param.clang_opt;
 	const char *template = llvm_param.clang_bpf_cmd_template;
+	char *kbuild_dir = NULL;
 	void *obj_buf = NULL;
 	size_t obj_buf_sz;
 
@@ -228,10 +298,16 @@ int llvm__compile_bpf(const char *path, void **p_obj_buf,
 		return -ENOENT;
 	}
 
+	/*
+	 * This is an optional work. Even it fail we can continue our
+	 * work. Needn't to check error return.
+	 */
+	get_kbuild_opts(&kbuild_dir);
+
 	force_set_env("CLANG_EXEC", clang_path);
 	force_set_env("CLANG_OPTIONS", clang_opt);
 	force_set_env("KERNEL_INC_OPTIONS", NULL);
-	force_set_env("WORKING_DIR", ".");
+	force_set_env("WORKING_DIR", kbuild_dir ? : ".");
 
 	/*
 	 * Since we may reset clang's working dir, path of source file
@@ -253,6 +329,7 @@ int llvm__compile_bpf(const char *path, void **p_obj_buf,
 		goto errout;
 	}
 
+	free(kbuild_dir);
 	if (!p_obj_buf)
 		free(obj_buf);
 	else
@@ -262,6 +339,7 @@ int llvm__compile_bpf(const char *path, void **p_obj_buf,
 		*p_obj_buf_sz = obj_buf_sz;
 	return 0;
 errout:
+	free(kbuild_dir);
 	free(obj_buf);
 	if (p_obj_buf)
 		*p_obj_buf = NULL;