Merge branch 'libbpf-support-module-function-syntax-for-tracing-programs'

Viktor Malik says:

====================
libbpf: support "module:function" syntax for tracing programs

In some situations, it is useful to explicitly specify a kernel module
to search for a tracing program target (e.g. when a function of the same
name exists in multiple modules or in vmlinux).

This change enables that by allowing the "module:function" syntax for
the find_kernel_btf_id function. Thanks to this, the syntax can be used
both from a SEC macro (i.e. `SEC(fentry/module:function)`) and via the
bpf_program__set_attach_target API call.
---

Changes in v2:
- stylistic changes (suggested by Andrii)
- added Andrii's ack to the second patch
====================

Link: https://lore.kernel.org/r/cover.1714469650.git.vmalik@redhat.com
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

3 files changed, 55 insertions, 9 deletions

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 7667671187e9..109b33fb68dc 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -9862,16 +9862,28 @@ static int find_kernel_btf_id(struct bpf_object *obj, const char *attach_name,
 			      enum bpf_attach_type attach_type,
 			      int *btf_obj_fd, int *btf_type_id)
 {
-	int ret, i;
+	int ret, i, mod_len;
+	const char *fn_name, *mod_name = NULL;
 
-	ret = find_attach_btf_id(obj->btf_vmlinux, attach_name, attach_type);
-	if (ret > 0) {
-		*btf_obj_fd = 0; /* vmlinux BTF */
-		*btf_type_id = ret;
-		return 0;
+	fn_name = strchr(attach_name, ':');
+	if (fn_name) {
+		mod_name = attach_name;
+		mod_len = fn_name - mod_name;
+		fn_name++;
+	}
+
+	if (!mod_name || strncmp(mod_name, "vmlinux", mod_len) == 0) {
+		ret = find_attach_btf_id(obj->btf_vmlinux,
+					 mod_name ? fn_name : attach_name,
+					 attach_type);
+		if (ret > 0) {
+			*btf_obj_fd = 0; /* vmlinux BTF */
+			*btf_type_id = ret;
+			return 0;
+		}
+		if (ret != -ENOENT)
+			return ret;
 	}
-	if (ret != -ENOENT)
-		return ret;
 
 	ret = load_module_btfs(obj);
 	if (ret)
@@ -9880,7 +9892,12 @@ static int find_kernel_btf_id(struct bpf_object *obj, const char *attach_name,
 	for (i = 0; i < obj->btf_module_cnt; i++) {
 		const struct module_btf *mod = &obj->btf_modules[i];
 
-		ret = find_attach_btf_id(mod->btf, attach_name, attach_type);
+		if (mod_name && strncmp(mod->name, mod_name, mod_len) != 0)
+			continue;
+
+		ret = find_attach_btf_id(mod->btf,
+					 mod_name ? fn_name : attach_name,
+					 attach_type);
 		if (ret > 0) {
 			*btf_obj_fd = mod->fd;
 			*btf_type_id = ret;
diff --git a/tools/testing/selftests/bpf/prog_tests/module_attach.c b/tools/testing/selftests/bpf/prog_tests/module_attach.c
index f53d658ed080..6d391d95f96e 100644
--- a/tools/testing/selftests/bpf/prog_tests/module_attach.c
+++ b/tools/testing/selftests/bpf/prog_tests/module_attach.c
@@ -51,6 +51,10 @@ void test_module_attach(void)
 					     0, "bpf_testmod_test_read");
 	ASSERT_OK(err, "set_attach_target");
 
+	err = bpf_program__set_attach_target(skel->progs.handle_fentry_explicit_manual,
+					     0, "bpf_testmod:bpf_testmod_test_read");
+	ASSERT_OK(err, "set_attach_target_explicit");
+
 	err = test_module_attach__load(skel);
 	if (CHECK(err, "skel_load", "failed to load skeleton\n"))
 		return;
@@ -70,6 +74,8 @@ void test_module_attach(void)
 	ASSERT_EQ(bss->tp_btf_read_sz, READ_SZ, "tp_btf");
 	ASSERT_EQ(bss->fentry_read_sz, READ_SZ, "fentry");
 	ASSERT_EQ(bss->fentry_manual_read_sz, READ_SZ, "fentry_manual");
+	ASSERT_EQ(bss->fentry_explicit_read_sz, READ_SZ, "fentry_explicit");
+	ASSERT_EQ(bss->fentry_explicit_manual_read_sz, READ_SZ, "fentry_explicit_manual");
 	ASSERT_EQ(bss->fexit_read_sz, READ_SZ, "fexit");
 	ASSERT_EQ(bss->fexit_ret, -EIO, "fexit_tet");
 	ASSERT_EQ(bss->fmod_ret_read_sz, READ_SZ, "fmod_ret");
diff --git a/tools/testing/selftests/bpf/progs/test_module_attach.c b/tools/testing/selftests/bpf/progs/test_module_attach.c
index 8a1b50f3a002..cc1a012d038f 100644
--- a/tools/testing/selftests/bpf/progs/test_module_attach.c
+++ b/tools/testing/selftests/bpf/progs/test_module_attach.c
@@ -73,6 +73,29 @@ int BPF_PROG(handle_fentry_manual,
 	return 0;
 }
 
+__u32 fentry_explicit_read_sz = 0;
+
+SEC("fentry/bpf_testmod:bpf_testmod_test_read")
+int BPF_PROG(handle_fentry_explicit,
+	     struct file *file, struct kobject *kobj,
+	     struct bin_attribute *bin_attr, char *buf, loff_t off, size_t len)
+{
+	fentry_explicit_read_sz = len;
+	return 0;
+}
+
+
+__u32 fentry_explicit_manual_read_sz = 0;
+
+SEC("fentry")
+int BPF_PROG(handle_fentry_explicit_manual,
+	     struct file *file, struct kobject *kobj,
+	     struct bin_attribute *bin_attr, char *buf, loff_t off, size_t len)
+{
+	fentry_explicit_manual_read_sz = len;
+	return 0;
+}
+
 __u32 fexit_read_sz = 0;
 int fexit_ret = 0;