selftests/bpf: add tests for the "module: Function" syntax

The previous patch added support for the "module:function" syntax for
tracing programs. This adds tests for explicitly specifying the module
name via the SEC macro and via the bpf_program__set_attach_target call.
Signed-off-by: Viktor Malik <vmalik@redhat.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/8a076168ed847f7c8a6c25715737b1fea84e38be.1714469650.git.vmalik@redhat.com

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");

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;