tools/perf/util/llvm-utils.c - kernel/msm-4.9 - Gitiles

 /*
  * Copyright (C) 2015, Wang Nan <wangnan0@huawei.com>
  * Copyright (C) 2015, Huawei Inc.
  */

 #include <stdio.h>
 #include <sys/utsname.h>
 #include "util.h"
 #include "debug.h"
 #include "llvm-utils.h"
 #include "cache.h"

 #define CLANG_BPF_CMD_DEFAULT_TEMPLATE				\
 		"$CLANG_EXEC -D__KERNEL__ $CLANG_OPTIONS "	\
 		"$KERNEL_INC_OPTIONS -Wno-unused-value "	\
 		"-Wno-pointer-sign -working-directory "		\
 		"$WORKING_DIR -c \"$CLANG_SOURCE\" -target bpf -O2 -o -"

 struct llvm_param llvm_param = {
 	.clang_path = "clang",
 	.clang_bpf_cmd_template = CLANG_BPF_CMD_DEFAULT_TEMPLATE,
 	.clang_opt = NULL,
 	.kbuild_dir = NULL,
 	.kbuild_opts = NULL,
 	.user_set_param = false,
 };

 int perf_llvm_config(const char *var, const char *value)
 {
 	if (prefixcmp(var, "llvm."))
 		return 0;
 	var += sizeof("llvm.") - 1;

 	if (!strcmp(var, "clang-path"))
 		llvm_param.clang_path = strdup(value);
 	else if (!strcmp(var, "clang-bpf-cmd-template"))
 		llvm_param.clang_bpf_cmd_template = strdup(value);
 	else if (!strcmp(var, "clang-opt"))
 		llvm_param.clang_opt = strdup(value);
 	else if (!strcmp(var, "kbuild-dir"))
 		llvm_param.kbuild_dir = strdup(value);
 	else if (!strcmp(var, "kbuild-opts"))
 		llvm_param.kbuild_opts = strdup(value);
 	else
 		return -1;
 	llvm_param.user_set_param = true;
 	return 0;
 }

 static int
 search_program(const char *def, const char *name,
 	       char *output)
 {
 	char *env, *path, *tmp = NULL;
 	char buf[PATH_MAX];
 	int ret;

 	output[0] = '\0';
 	if (def && def[0] != '\0') {
 		if (def[0] == '/') {
 			if (access(def, F_OK) == 0) {
 				strlcpy(output, def, PATH_MAX);
 				return 0;
 			}
 		} else if (def[0] != '\0')
 			name = def;
 	}

 	env = getenv("PATH");
 	if (!env)
 		return -1;
 	env = strdup(env);
 	if (!env)
 		return -1;

 	ret = -ENOENT;
 	path = strtok_r(env, ":",  &tmp);
 	while (path) {
 		scnprintf(buf, sizeof(buf), "%s/%s", path, name);
 		if (access(buf, F_OK) == 0) {
 			strlcpy(output, buf, PATH_MAX);
 			ret = 0;
 			break;
 		}
 		path = strtok_r(NULL, ":", &tmp);
 	}

 	free(env);
 	return ret;
 }

 #define READ_SIZE	4096
 static int
 read_from_pipe(const char *cmd, void **p_buf, size_t *p_read_sz)
 {
 	int err = 0;
 	void *buf = NULL;
 	FILE *file = NULL;
 	size_t read_sz = 0, buf_sz = 0;

 	file = popen(cmd, "r");
 	if (!file) {
 		pr_err("ERROR: unable to popen cmd: %s\n",
 		       strerror(errno));
 		return -EINVAL;
 	}

 	while (!feof(file) && !ferror(file)) {
 		/*
 		 * Make buf_sz always have obe byte extra space so we
 		 * can put '\0' there.
 		 */
 		if (buf_sz - read_sz < READ_SIZE + 1) {
 			void *new_buf;

 			buf_sz = read_sz + READ_SIZE + 1;
 			new_buf = realloc(buf, buf_sz);

 			if (!new_buf) {
 				pr_err("ERROR: failed to realloc memory\n");
 				err = -ENOMEM;
 				goto errout;
 			}

 			buf = new_buf;
 		}
 		read_sz += fread(buf + read_sz, 1, READ_SIZE, file);
 	}

 	if (buf_sz - read_sz < 1) {
 		pr_err("ERROR: internal error\n");
 		err = -EINVAL;
 		goto errout;
 	}

 	if (ferror(file)) {
 		pr_err("ERROR: error occurred when reading from pipe: %s\n",
 		       strerror(errno));
 		err = -EIO;
 		goto errout;
 	}

 	err = WEXITSTATUS(pclose(file));
 	file = NULL;
 	if (err) {
 		err = -EINVAL;
 		goto errout;
 	}

 	/*
 	 * If buf is string, give it terminal '\0' to make our life
 	 * easier. If buf is not string, that '\0' is out of space
 	 * indicated by read_sz so caller won't even notice it.
 	 */
 	((char *)buf)[read_sz] = '\0';

 	if (!p_buf)
 		free(buf);
 	else
 		*p_buf = buf;

 	if (p_read_sz)
 		*p_read_sz = read_sz;
 	return 0;

 errout:
 	if (file)
 		pclose(file);
 	free(buf);
 	if (p_buf)
 		*p_buf = NULL;
 	if (p_read_sz)
 		*p_read_sz = 0;
 	return err;
 }

 static inline void
 force_set_env(const char *var, const char *value)
 {
 	if (value) {
 		setenv(var, value, 1);
 		pr_debug("set env: %s=%s\n", var, value);
 	} else {
 		unsetenv(var);
 		pr_debug("unset env: %s\n", var);
 	}
 }

 static void
 version_notice(void)
 {
 	pr_err(
 "     \tLLVM 3.7 or newer is required. Which can be found from http://llvm.org\n"
 "     \tYou may want to try git trunk:\n"
 "     \t\tgit clone http://llvm.org/git/llvm.git\n"
 "     \t\t     and\n"
 "     \t\tgit clone http://llvm.org/git/clang.git\n\n"
 "     \tOr fetch the latest clang/llvm 3.7 from pre-built llvm packages for\n"
 "     \tdebian/ubuntu:\n"
 "     \t\thttp://llvm.org/apt\n\n"
 "     \tIf you are using old version of clang, change 'clang-bpf-cmd-template'\n"
 "     \toption in [llvm] section of ~/.perfconfig to:\n\n"
 "     \t  \"$CLANG_EXEC $CLANG_OPTIONS $KERNEL_INC_OPTIONS \\\n"
 "     \t     -working-directory $WORKING_DIR -c $CLANG_SOURCE \\\n"
 "     \t     -emit-llvm -o - | /path/to/llc -march=bpf -filetype=obj -o -\"\n"
 "     \t(Replace /path/to/llc with path to your llc)\n\n"
 );
 }

 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 const char *kinc_fetch_script =
 "#!/usr/bin/env sh\n"
 "if ! test -d \"$KBUILD_DIR\"\n"
 "then\n"
 "	exit -1\n"
 "fi\n"
 "if ! test -f \"$KBUILD_DIR/include/generated/autoconf.h\"\n"
 "then\n"
 "	exit -1\n"
 "fi\n"
 "TMPDIR=`mktemp -d`\n"
 "if test -z \"$TMPDIR\"\n"
 "then\n"
 "    exit -1\n"
 "fi\n"
 "cat << EOF > $TMPDIR/Makefile\n"
 "obj-y := dummy.o\n"
 "\\$(obj)/%.o: \\$(src)/%.c\n"
 "\t@echo -n \"\\$(NOSTDINC_FLAGS) \\$(LINUXINCLUDE) \\$(EXTRA_CFLAGS)\"\n"
 "EOF\n"
 "touch $TMPDIR/dummy.c\n"
 "make -s -C $KBUILD_DIR M=$TMPDIR $KBUILD_OPTS dummy.o 2>/dev/null\n"
 "RET=$?\n"
 "rm -rf $TMPDIR\n"
 "exit $RET\n";

 static inline void
 get_kbuild_opts(char **kbuild_dir, char **kbuild_include_opts)
 {
 	int err;

 	if (!kbuild_dir || !kbuild_include_opts)
 		return;

 	*kbuild_dir = NULL;
 	*kbuild_include_opts = 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;
 	}

 	pr_debug("Kernel build dir is set to %s\n", *kbuild_dir);
 	force_set_env("KBUILD_DIR", *kbuild_dir);
 	force_set_env("KBUILD_OPTS", llvm_param.kbuild_opts);
 	err = read_from_pipe(kinc_fetch_script,
 			     (void **)kbuild_include_opts,
 			     NULL);
 	if (err) {
 		pr_warning(
 "WARNING:\tunable to get kernel include directories from '%s'\n"
 "Hint:\tTry set clang include options using 'clang-bpf-cmd-template'\n"
 "     \toption in [llvm] section of ~/.perfconfig and set 'kbuild-dir'\n"
 "     \toption in [llvm] to \"\" to suppress this detection.\n\n",
 			*kbuild_dir);

 		free(*kbuild_dir);
 		*kbuild_dir = NULL;
 		return;
 	}

 	pr_debug("include option is set to %s\n", *kbuild_include_opts);
 }

 int llvm__compile_bpf(const char *path, void **p_obj_buf,
 		      size_t *p_obj_buf_sz)
 {
 	int err;
 	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, *kbuild_include_opts = NULL;
 	void *obj_buf = NULL;
 	size_t obj_buf_sz;

 	if (!template)
 		template = CLANG_BPF_CMD_DEFAULT_TEMPLATE;

 	err = search_program(llvm_param.clang_path,
 			     "clang", clang_path);
 	if (err) {
 		pr_err(
 "ERROR:\tunable to find clang.\n"
 "Hint:\tTry to install latest clang/llvm to support BPF. Check your $PATH\n"
 "     \tand 'clang-path' option in [llvm] section of ~/.perfconfig.\n");
 		version_notice();
 		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, &kbuild_include_opts);

 	force_set_env("CLANG_EXEC", clang_path);
 	force_set_env("CLANG_OPTIONS", clang_opt);
 	force_set_env("KERNEL_INC_OPTIONS", kbuild_include_opts);
 	force_set_env("WORKING_DIR", kbuild_dir ? : ".");

 	/*
 	 * Since we may reset clang's working dir, path of source file
 	 * should be transferred into absolute path, except we want
 	 * stdin to be source file (testing).
 	 */
 	force_set_env("CLANG_SOURCE",
 		      (path[0] == '-') ? path :
 		      make_nonrelative_path(path));

 	pr_debug("llvm compiling command template: %s\n", template);
 	err = read_from_pipe(template, &obj_buf, &obj_buf_sz);
 	if (err) {
 		pr_err("ERROR:\tunable to compile %s\n", path);
 		pr_err("Hint:\tCheck error message shown above.\n");
 		pr_err("Hint:\tYou can also pre-compile it into .o using:\n");
 		pr_err("     \t\tclang -target bpf -O2 -c %s\n", path);
 		pr_err("     \twith proper -I and -D options.\n");
 		goto errout;
 	}

 	free(kbuild_dir);
 	free(kbuild_include_opts);
 	if (!p_obj_buf)
 		free(obj_buf);
 	else
 		*p_obj_buf = obj_buf;

 	if (p_obj_buf_sz)
 		*p_obj_buf_sz = obj_buf_sz;
 	return 0;
 errout:
 	free(kbuild_dir);
 	free(kbuild_include_opts);
 	free(obj_buf);
 	if (p_obj_buf)
 		*p_obj_buf = NULL;
 	if (p_obj_buf_sz)
 		*p_obj_buf_sz = 0;
 	return err;
 }

 int llvm__search_clang(void)
 {
 	char clang_path[PATH_MAX];

 	return search_program(llvm_param.clang_path, "clang", clang_path);
 }
	/*
	* Copyright (C) 2015, Wang Nan <wangnan0@huawei.com>
	* Copyright (C) 2015, Huawei Inc.
	*/

	#include <stdio.h>
	#include <sys/utsname.h>
	#include "util.h"
	#include "debug.h"
	#include "llvm-utils.h"
	#include "cache.h"

	#define CLANG_BPF_CMD_DEFAULT_TEMPLATE \
	"$CLANG_EXEC -D__KERNEL__ $CLANG_OPTIONS " \
	"$KERNEL_INC_OPTIONS -Wno-unused-value " \
	"-Wno-pointer-sign -working-directory " \
	"$WORKING_DIR -c \"$CLANG_SOURCE\" -target bpf -O2 -o -"

	struct llvm_param llvm_param = {
	.clang_path = "clang",
	.clang_bpf_cmd_template = CLANG_BPF_CMD_DEFAULT_TEMPLATE,
	.clang_opt = NULL,
	.kbuild_dir = NULL,
	.kbuild_opts = NULL,
	.user_set_param = false,
	};

	int perf_llvm_config(const char var, const char value)
	{
	if (prefixcmp(var, "llvm."))
	return 0;
	var += sizeof("llvm.") - 1;

	if (!strcmp(var, "clang-path"))
	llvm_param.clang_path = strdup(value);
	else if (!strcmp(var, "clang-bpf-cmd-template"))
	llvm_param.clang_bpf_cmd_template = strdup(value);
	else if (!strcmp(var, "clang-opt"))
	llvm_param.clang_opt = strdup(value);
	else if (!strcmp(var, "kbuild-dir"))
	llvm_param.kbuild_dir = strdup(value);
	else if (!strcmp(var, "kbuild-opts"))
	llvm_param.kbuild_opts = strdup(value);
	else
	return -1;
	llvm_param.user_set_param = true;
	return 0;
	}

	static int
	search_program(const char def, const char name,
	char *output)
	{
	char env, path, *tmp = NULL;
	char buf[PATH_MAX];
	int ret;

	output[0] = '\0';
	if (def && def[0] != '\0') {
	if (def[0] == '/') {
	if (access(def, F_OK) == 0) {
	strlcpy(output, def, PATH_MAX);
	return 0;
	}
	} else if (def[0] != '\0')
	name = def;
	}

	env = getenv("PATH");
	if (!env)
	return -1;
	env = strdup(env);
	if (!env)
	return -1;

	ret = -ENOENT;
	path = strtok_r(env, ":", &tmp);
	while (path) {
	scnprintf(buf, sizeof(buf), "%s/%s", path, name);
	if (access(buf, F_OK) == 0) {
	strlcpy(output, buf, PATH_MAX);
	ret = 0;
	break;
	}
	path = strtok_r(NULL, ":", &tmp);
	}

	free(env);
	return ret;
	}

	#define READ_SIZE 4096
	static int
	read_from_pipe(const char cmd, void p_buf, size_t p_read_sz)
	{
	int err = 0;
	void *buf = NULL;
	FILE *file = NULL;
	size_t read_sz = 0, buf_sz = 0;

	file = popen(cmd, "r");
	if (!file) {
	pr_err("ERROR: unable to popen cmd: %s\n",
	strerror(errno));
	return -EINVAL;
	}

	while (!feof(file) && !ferror(file)) {
	/*
	* Make buf_sz always have obe byte extra space so we
	* can put '\0' there.
	*/
	if (buf_sz - read_sz < READ_SIZE + 1) {
	void *new_buf;

	buf_sz = read_sz + READ_SIZE + 1;
	new_buf = realloc(buf, buf_sz);

	if (!new_buf) {
	pr_err("ERROR: failed to realloc memory\n");
	err = -ENOMEM;
	goto errout;
	}

	buf = new_buf;
	}
	read_sz += fread(buf + read_sz, 1, READ_SIZE, file);
	}

	if (buf_sz - read_sz < 1) {
	pr_err("ERROR: internal error\n");
	err = -EINVAL;
	goto errout;
	}

	if (ferror(file)) {
	pr_err("ERROR: error occurred when reading from pipe: %s\n",
	strerror(errno));
	err = -EIO;
	goto errout;
	}

	err = WEXITSTATUS(pclose(file));
	file = NULL;
	if (err) {
	err = -EINVAL;
	goto errout;
	}

	/*
	* If buf is string, give it terminal '\0' to make our life
	* easier. If buf is not string, that '\0' is out of space
	* indicated by read_sz so caller won't even notice it.
	*/
	((char *)buf)[read_sz] = '\0';

	if (!p_buf)
	free(buf);
	else
	*p_buf = buf;

	if (p_read_sz)
	*p_read_sz = read_sz;
	return 0;

	errout:
	if (file)
	pclose(file);
	free(buf);
	if (p_buf)
	*p_buf = NULL;
	if (p_read_sz)
	*p_read_sz = 0;
	return err;
	}

	static inline void
	force_set_env(const char var, const char value)
	{
	if (value) {
	setenv(var, value, 1);
	pr_debug("set env: %s=%s\n", var, value);
	} else {
	unsetenv(var);
	pr_debug("unset env: %s\n", var);
	}
	}

	static void
	version_notice(void)
	{
	pr_err(
	" \tLLVM 3.7 or newer is required. Which can be found from http://llvm.org\n"
	" \tYou may want to try git trunk:\n"
	" \t\tgit clone http://llvm.org/git/llvm.git\n"
	" \t\t and\n"
	" \t\tgit clone http://llvm.org/git/clang.git\n\n"
	" \tOr fetch the latest clang/llvm 3.7 from pre-built llvm packages for\n"
	" \tdebian/ubuntu:\n"
	" \t\thttp://llvm.org/apt\n\n"
	" \tIf you are using old version of clang, change 'clang-bpf-cmd-template'\n"
	" \toption in [llvm] section of ~/.perfconfig to:\n\n"
	" \t \"$CLANG_EXEC $CLANG_OPTIONS $KERNEL_INC_OPTIONS \\\n"
	" \t -working-directory $WORKING_DIR -c $CLANG_SOURCE \\\n"
	" \t -emit-llvm -o - \| /path/to/llc -march=bpf -filetype=obj -o -\"\n"
	" \t(Replace /path/to/llc with path to your llc)\n\n"
	);
	}

	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 const char *kinc_fetch_script =
	"#!/usr/bin/env sh\n"
	"if ! test -d \"$KBUILD_DIR\"\n"
	"then\n"
	" exit -1\n"
	"fi\n"
	"if ! test -f \"$KBUILD_DIR/include/generated/autoconf.h\"\n"
	"then\n"
	" exit -1\n"
	"fi\n"
	"TMPDIR=`mktemp -d`\n"
	"if test -z \"$TMPDIR\"\n"
	"then\n"
	" exit -1\n"
	"fi\n"
	"cat << EOF > $TMPDIR/Makefile\n"
	"obj-y := dummy.o\n"
	"\\$(obj)/%.o: \\$(src)/%.c\n"
	"\t@echo -n \"\\$(NOSTDINC_FLAGS) \\$(LINUXINCLUDE) \\$(EXTRA_CFLAGS)\"\n"
	"EOF\n"
	"touch $TMPDIR/dummy.c\n"
	"make -s -C $KBUILD_DIR M=$TMPDIR $KBUILD_OPTS dummy.o 2>/dev/null\n"
	"RET=$?\n"
	"rm -rf $TMPDIR\n"
	"exit $RET\n";

	static inline void
	get_kbuild_opts(char kbuild_dir, char kbuild_include_opts)
	{
	int err;

	if (!kbuild_dir \|\| !kbuild_include_opts)
	return;

	*kbuild_dir = NULL;
	*kbuild_include_opts = 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;
	}

	pr_debug("Kernel build dir is set to %s\n", *kbuild_dir);
	force_set_env("KBUILD_DIR", *kbuild_dir);
	force_set_env("KBUILD_OPTS", llvm_param.kbuild_opts);
	err = read_from_pipe(kinc_fetch_script,
	(void **)kbuild_include_opts,
	NULL);
	if (err) {
	pr_warning(
	"WARNING:\tunable to get kernel include directories from '%s'\n"
	"Hint:\tTry set clang include options using 'clang-bpf-cmd-template'\n"
	" \toption in [llvm] section of ~/.perfconfig and set 'kbuild-dir'\n"
	" \toption in [llvm] to \"\" to suppress this detection.\n\n",
	*kbuild_dir);

	free(*kbuild_dir);
	*kbuild_dir = NULL;
	return;
	}

	pr_debug("include option is set to %s\n", *kbuild_include_opts);
	}

	int llvm__compile_bpf(const char path, void *p_obj_buf,
	size_t *p_obj_buf_sz)
	{
	int err;
	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, kbuild_include_opts = NULL;
	void *obj_buf = NULL;
	size_t obj_buf_sz;

	if (!template)
	template = CLANG_BPF_CMD_DEFAULT_TEMPLATE;

	err = search_program(llvm_param.clang_path,
	"clang", clang_path);
	if (err) {
	pr_err(
	"ERROR:\tunable to find clang.\n"
	"Hint:\tTry to install latest clang/llvm to support BPF. Check your $PATH\n"
	" \tand 'clang-path' option in [llvm] section of ~/.perfconfig.\n");
	version_notice();
	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, &kbuild_include_opts);

	force_set_env("CLANG_EXEC", clang_path);
	force_set_env("CLANG_OPTIONS", clang_opt);
	force_set_env("KERNEL_INC_OPTIONS", kbuild_include_opts);
	force_set_env("WORKING_DIR", kbuild_dir ? : ".");

	/*
	* Since we may reset clang's working dir, path of source file
	* should be transferred into absolute path, except we want
	* stdin to be source file (testing).
	*/
	force_set_env("CLANG_SOURCE",
	(path[0] == '-') ? path :
	make_nonrelative_path(path));

	pr_debug("llvm compiling command template: %s\n", template);
	err = read_from_pipe(template, &obj_buf, &obj_buf_sz);
	if (err) {
	pr_err("ERROR:\tunable to compile %s\n", path);
	pr_err("Hint:\tCheck error message shown above.\n");
	pr_err("Hint:\tYou can also pre-compile it into .o using:\n");
	pr_err(" \t\tclang -target bpf -O2 -c %s\n", path);
	pr_err(" \twith proper -I and -D options.\n");
	goto errout;
	}

	free(kbuild_dir);
	free(kbuild_include_opts);
	if (!p_obj_buf)
	free(obj_buf);
	else
	*p_obj_buf = obj_buf;

	if (p_obj_buf_sz)
	*p_obj_buf_sz = obj_buf_sz;
	return 0;
	errout:
	free(kbuild_dir);
	free(kbuild_include_opts);
	free(obj_buf);
	if (p_obj_buf)
	*p_obj_buf = NULL;
	if (p_obj_buf_sz)
	*p_obj_buf_sz = 0;
	return err;
	}

	int llvm__search_clang(void)
	{
	char clang_path[PATH_MAX];

	return search_program(llvm_param.clang_path, "clang", clang_path);
	}