Merge branch 'selftests/bpf: Add read_build_id function'

Jiri Olsa says:

====================

hi,
this selftests cleanup was previously posted as part of file build id changes [1],
which might take more time, so I'm sending the selftests changes separately so it
won't get stuck.

v4 changes:
  - added size argument to read_build_id [Andrii]
  - condition changes in parse_build_id_buf [Andrii]
  - use ELF_C_READ_MMAP in elf_begin [Andrii]
  - return -ENOENT in read_build_id if build id is not found [Andrii]
  - dropped elf class check [Andrii]

thanks,
jirka

[1] https://lore.kernel.org/bpf/20230316170149.4106586-1-jolsa@kernel.org/
====================

Signed-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 @@ retry:
 		  "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 @@ retry:
 		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 @@ retry:
 		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 @@ retry:
 		  "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 @@ retry:
 		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 @@ retry:
 		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/progs/err.h

@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ERR_H__
+#define __ERR_H__
+
+#define MAX_ERRNO 4095
+#define IS_ERR_VALUE(x) (unsigned long)(void *)(x) >= (unsigned long)-MAX_ERRNO
+
+static inline int IS_ERR_OR_NULL(const void *ptr)
+{
+	return !ptr || IS_ERR_VALUE((unsigned long)ptr);
+}
+
+static inline long PTR_ERR(const void *ptr)
+{
+	return (long) ptr;
+}
+
+#endif /* __ERR_H__ */

tools/testing/selftests/bpf/progs/profiler.inc.h

@@ -6,6 +6,7 @@
 #include <bpf/bpf_tracing.h>
 
 #include "profiler.h"
+#include "err.h"
 
 #ifndef NULL
 #define NULL 0
@@ -16,7 +17,6 @@
 #define O_DIRECTORY 00200000
 #define __O_TMPFILE 020000000
 #define O_TMPFILE (__O_TMPFILE | O_DIRECTORY)
-#define MAX_ERRNO 4095
 #define S_IFMT 00170000
 #define S_IFSOCK 0140000
 #define S_IFLNK 0120000
@@ -34,7 +34,6 @@
 #define S_ISBLK(m) (((m)&S_IFMT) == S_IFBLK)
 #define S_ISFIFO(m) (((m)&S_IFMT) == S_IFIFO)
 #define S_ISSOCK(m) (((m)&S_IFMT) == S_IFSOCK)
-#define IS_ERR_VALUE(x) (unsigned long)(void*)(x) >= (unsigned long)-MAX_ERRNO
 
 #define KILL_DATA_ARRAY_SIZE 8
 

tools/testing/selftests/bpf/test_progs.c

@@ -629,31 +629,6 @@ out:
 	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);

tools/testing/selftests/bpf/trace_helpers.c

@@ -11,6 +11,9 @@
 #include <linux/perf_event.h>
 #include <sys/mman.h>
 #include "trace_helpers.h"
+#include <linux/limits.h>
+#include <libelf.h>
+#include <gelf.h>
 
 #define TRACEFS_PIPE	"/sys/kernel/tracing/trace_pipe"
 #define DEBUGFS_PIPE	"/sys/kernel/debug/tracing/trace_pipe"
@@ -234,3 +237,82 @@ ssize_t get_rel_offset(uintptr_t addr)
 	fclose(f);
 	return -EINVAL;
 }
+
+static int
+parse_build_id_buf(const void *note_start, Elf32_Word note_size, char *build_id)
+{
+	Elf32_Word note_offs = 0;
+
+	while (note_offs + sizeof(Elf32_Nhdr) < note_size) {
+		Elf32_Nhdr *nhdr = (Elf32_Nhdr *)(note_start + note_offs);
+
+		if (nhdr->n_type == 3 && nhdr->n_namesz == sizeof("GNU") &&
+		    !strcmp((char *)(nhdr + 1), "GNU") && nhdr->n_descsz > 0 &&
+		    nhdr->n_descsz <= BPF_BUILD_ID_SIZE) {
+			memcpy(build_id, note_start + note_offs +
+			       ALIGN(sizeof("GNU"), 4) + sizeof(Elf32_Nhdr), nhdr->n_descsz);
+			memset(build_id + nhdr->n_descsz, 0, BPF_BUILD_ID_SIZE - nhdr->n_descsz);
+			return (int) nhdr->n_descsz;
+		}
+
+		note_offs = note_offs + sizeof(Elf32_Nhdr) +
+			   ALIGN(nhdr->n_namesz, 4) + ALIGN(nhdr->n_descsz, 4);
+	}
+
+	return -ENOENT;
+}
+
+/* Reads binary from *path* file and returns it in the *build_id* buffer
+ * with *size* which is expected to be at least BPF_BUILD_ID_SIZE bytes.
+ * Returns size of build id on success. On error the error value is
+ * returned.
+ */
+int read_build_id(const char *path, char *build_id, size_t size)
+{
+	int fd, err = -EINVAL;
+	Elf *elf = NULL;
+	GElf_Ehdr ehdr;
+	size_t max, i;
+
+	if (size < BPF_BUILD_ID_SIZE)
+		return -EINVAL;
+
+	fd = open(path, O_RDONLY | O_CLOEXEC);
+	if (fd < 0)
+		return -errno;
+
+	(void)elf_version(EV_CURRENT);
+
+	elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
+	if (!elf)
+		goto out;
+	if (elf_kind(elf) != ELF_K_ELF)
+		goto out;
+	if (!gelf_getehdr(elf, &ehdr))
+		goto out;
+
+	for (i = 0; i < ehdr.e_phnum; i++) {
+		GElf_Phdr mem, *phdr;
+		char *data;
+
+		phdr = gelf_getphdr(elf, i, &mem);
+		if (!phdr)
+			goto out;
+		if (phdr->p_type != PT_NOTE)
+			continue;
+		data = elf_rawfile(elf, &max);
+		if (!data)
+			goto out;
+		if (phdr->p_offset + phdr->p_memsz > max)
+			goto out;
+		err = parse_build_id_buf(data + phdr->p_offset, phdr->p_memsz, build_id);
+		if (err > 0)
+			break;
+	}
+
+out:
+	if (elf)
+		elf_end(elf);
+	close(fd);
+	return err;
+}

tools/testing/selftests/bpf/trace_helpers.h

@@ -4,6 +4,9 @@
 
 #include <bpf/libbpf.h>
 
+#define __ALIGN_MASK(x, mask)	(((x)+(mask))&~(mask))
+#define ALIGN(x, a)		__ALIGN_MASK(x, (typeof(x))(a)-1)
+
 struct ksym {
 	long addr;
 	char *name;
@@ -23,4 +26,6 @@ void read_trace_pipe(void);
 ssize_t get_uprobe_offset(const void *addr);
 ssize_t get_rel_offset(uintptr_t addr);
 
+int read_build_id(const char *path, char *build_id, size_t size);
+
 #endif