[PATCH 1/2] perf llvm: Allow dump llvm output object file using llvm.dump-obj

[Wang Nan]

Add a 'llvm.dump-obj' config option to enable perf dump BPF object files
compiled by LLVM.

This option is useful when using BPF objects in embedded platforms.
LLVM compiler won't be deployed in these platforms, and currently we
don't support dynamic compiling library.

Before this patch users have to explicitly issue llvm commands to
compile BPF scripts, and can't use helpers (like include path detection
and default macros) in perf. With this option, user is allowed to use
perf to compile their BPF objects then copy them into their embedded
platforms.

Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
---
 tools/perf/util/llvm-utils.c | 42 ++++++++++++++++++++++++++++++++++++++++++
 tools/perf/util/llvm-utils.h |  5 +++++
 2 files changed, 47 insertions(+)

diff --git a/tools/perf/util/llvm-utils.c b/tools/perf/util/llvm-utils.c
index 33071d6..ede8f7d 100644
--- a/tools/perf/util/llvm-utils.c
+++ b/tools/perf/util/llvm-utils.c
@@ -42,6 +42,8 @@ int perf_llvm_config(const char *var, const char *value)
 		llvm_param.kbuild_dir = strdup(value);
 	else if (!strcmp(var, "kbuild-opts"))
 		llvm_param.kbuild_opts = strdup(value);
+	else if (!strcmp(var, "dump-obj"))
+		llvm_param.dump_obj = !!perf_config_bool(var, value);
 	else
 		return -1;
 	llvm_param.user_set_param = true;
@@ -326,6 +328,42 @@ get_kbuild_opts(char **kbuild_dir, char **kbuild_include_opts)
 	pr_debug("include option is set to %s\n", *kbuild_include_opts);
 }
 
+static void
+dump_obj(const char *path, void *obj_buf, size_t size)
+{
+	char *obj_path = strdup(path);
+	FILE *fp;
+	char *p;
+
+	if (!obj_path) {
+		pr_warning("WARNING: No enough memory, skip object dumpping\n");
+		return;
+	}
+
+	p = strrchr(obj_path, '.');
+	if (!p || (strcmp(p, ".c") != 0)) {
+		pr_warning("WARNING: invalid llvm source path: '%s', skip object dumpping\n",
+			   obj_path);
+		goto out;
+	}
+
+	p[1] = 'o';
+	fp = fopen(obj_path, "wb");
+	if (!fp) {
+		pr_warning("WARNING: failed to open '%s': %s, skip object dumpping\n",
+			   obj_path, strerror(errno));
+		goto out;
+	}
+
+	pr_info("LLVM: dumpping %s\n", obj_path);
+	if (fwrite(obj_buf, size, 1, fp) != 1)
+		pr_warning("WARNING: failed to write to file '%s': %s, skip object dumpping\n",
+			   obj_path, strerror(errno));
+	fclose(fp);
+out:
+	free(obj_path);
+}
+
 int llvm__compile_bpf(const char *path, void **p_obj_buf,
 		      size_t *p_obj_buf_sz)
 {
@@ -411,6 +449,10 @@ int llvm__compile_bpf(const char *path, void **p_obj_buf,
 
 	free(kbuild_dir);
 	free(kbuild_include_opts);
+
+	if (llvm_param.dump_obj)
+		dump_obj(path, obj_buf, obj_buf_sz);
+
 	if (!p_obj_buf)
 		free(obj_buf);
 	else
diff --git a/tools/perf/util/llvm-utils.h b/tools/perf/util/llvm-utils.h
index 23b9a74..9f501ce 100644
--- a/tools/perf/util/llvm-utils.h
+++ b/tools/perf/util/llvm-utils.h
@@ -30,6 +30,11 @@ struct llvm_param {
 	 */
 	const char *kbuild_opts;
 	/*
+	 * Default is false. If set to true, write compiling result
+	 * to object file.
+	 */
+	bool dump_obj;
+	/*
 	 * Default is false. If one of the above fields is set by user
 	 * explicitly then user_set_llvm is set to true. This is used
 	 * for perf test. If user doesn't set anything in .perfconfig
-- 
1.8.3.4