selftests/bpf: Replace extract_build_id with read_build_id

Replacing extract_build_id with read_build_id that parses out
build id directly from elf without using readelf tool.
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20230331093157.1749137-4-jolsa@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

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

@@ -7,13 +7,12 @@ void test_stacktrace_build_id(void)
 
 	int control_map_fd, stackid_hmap_fd, stackmap_fd, stack_amap_fd;
 	struct test_stacktrace_build_id *skel;
-	int err, stack_trace_len;
+	int err, stack_trace_len, build_id_size;
 	__u32 key, prev_key, val, duration = 0;
-	char buf[256];
-	int i, j;
+	char buf[BPF_BUILD_ID_SIZE];
 	struct bpf_stack_build_id id_offs[PERF_MAX_STACK_DEPTH];
 	int build_id_matches = 0;
-	int retry = 1;
+	int i, retry = 1;
 
 retry:
 	skel = test_stacktrace_build_id__open_and_load();
@@ -52,9 +51,10 @@ void test_stacktrace_build_id(void)
 		  "err %d errno %d\n", err, errno))
 		goto cleanup;
 
-	err = extract_build_id(buf, 256);
+	build_id_size = read_build_id("urandom_read", buf, sizeof(buf));
+	err = build_id_size < 0 ? build_id_size : 0;
 
-	if (CHECK(err, "get build_id with readelf",
+	if (CHECK(err, "read_build_id",
 		  "err %d errno %d\n", err, errno))
 		goto cleanup;
 
@@ -64,8 +64,6 @@ void test_stacktrace_build_id(void)
 		goto cleanup;
 
 	do {
-		char build_id[64];
-
 		err = bpf_map_lookup_elem(stackmap_fd, &key, id_offs);
 		if (CHECK(err, "lookup_elem from stackmap",
 			  "err %d, errno %d\n", err, errno))
@@ -73,10 +71,7 @@ void test_stacktrace_build_id(void)
 		for (i = 0; i < PERF_MAX_STACK_DEPTH; ++i)
 			if (id_offs[i].status == BPF_STACK_BUILD_ID_VALID &&
 			    id_offs[i].offset != 0) {
-				for (j = 0; j < 20; ++j)
-					sprintf(build_id + 2 * j, "%02x",
-						id_offs[i].build_id[j] & 0xff);
-				if (strstr(buf, build_id) != NULL)
+				if (memcmp(buf, id_offs[i].build_id, build_id_size) == 0)
 					build_id_matches = 1;
 			}
 		prev_key = key;

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

@@ -28,11 +28,10 @@ void test_stacktrace_build_id_nmi(void)
 		.config = PERF_COUNT_HW_CPU_CYCLES,
 	};
 	__u32 key, prev_key, val, duration = 0;
-	char buf[256];
-	int i, j;
+	char buf[BPF_BUILD_ID_SIZE];
 	struct bpf_stack_build_id id_offs[PERF_MAX_STACK_DEPTH];
-	int build_id_matches = 0;
-	int retry = 1;
+	int build_id_matches = 0, build_id_size;
+	int i, retry = 1;
 
 	attr.sample_freq = read_perf_max_sample_freq();
 
@@ -94,7 +93,8 @@ void test_stacktrace_build_id_nmi(void)
 		  "err %d errno %d\n", err, errno))
 		goto cleanup;
 
-	err = extract_build_id(buf, 256);
+	build_id_size = read_build_id("urandom_read", buf, sizeof(buf));
+	err = build_id_size < 0 ? build_id_size : 0;
 
 	if (CHECK(err, "get build_id with readelf",
 		  "err %d errno %d\n", err, errno))
@@ -106,8 +106,6 @@ void test_stacktrace_build_id_nmi(void)
 		goto cleanup;
 
 	do {
-		char build_id[64];
-
 		err = bpf_map__lookup_elem(skel->maps.stackmap, &key, sizeof(key),
 					   id_offs, sizeof(id_offs), 0);
 		if (CHECK(err, "lookup_elem from stackmap",
@@ -116,10 +114,7 @@ void test_stacktrace_build_id_nmi(void)
 		for (i = 0; i < PERF_MAX_STACK_DEPTH; ++i)
 			if (id_offs[i].status == BPF_STACK_BUILD_ID_VALID &&
 			    id_offs[i].offset != 0) {
-				for (j = 0; j < 20; ++j)
-					sprintf(build_id + 2 * j, "%02x",
-						id_offs[i].build_id[j] & 0xff);
-				if (strstr(buf, build_id) != NULL)
+				if (memcmp(buf, id_offs[i].build_id, build_id_size) == 0)
 					build_id_matches = 1;
 			}
 		prev_key = key;

tools/testing/selftests/bpf/test_progs.c

@@ -629,31 +629,6 @@ int compare_stack_ips(int smap_fd, int amap_fd, int stack_trace_len)
 	return err;
 }
 
-int extract_build_id(char *build_id, size_t size)
-{
-	FILE *fp;
-	char *line = NULL;
-	size_t len = 0;
-
-	fp = popen("readelf -n ./urandom_read | grep 'Build ID'", "r");
-	if (fp == NULL)
-		return -1;
-
-	if (getline(&line, &len, fp) == -1)
-		goto err;
-	pclose(fp);
-
-	if (len > size)
-		len = size;
-	memcpy(build_id, line, len);
-	build_id[len] = '\0';
-	free(line);
-	return 0;
-err:
-	pclose(fp);
-	return -1;
-}
-
 static int finit_module(int fd, const char *param_values, int flags)
 {
 	return syscall(__NR_finit_module, fd, param_values, flags);

tools/testing/selftests/bpf/test_progs.h

@@ -405,7 +405,6 @@ static inline void *u64_to_ptr(__u64 ptr)
 int bpf_find_map(const char *test, struct bpf_object *obj, const char *name);
 int compare_map_keys(int map1_fd, int map2_fd);
 int compare_stack_ips(int smap_fd, int amap_fd, int stack_trace_len);
-int extract_build_id(char *build_id, size_t size);
 int kern_sync_rcu(void);
 int trigger_module_test_read(int read_sz);
 int trigger_module_test_write(int write_sz);