selftests/bpf: Add tp_btf CO-RE reloc test for modules

Add another CO-RE relocation test for kernel module relocations. This time for
tp_btf with direct memory reads.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20201203204634.1325171-14-andrii@kernel.org

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

@@ -514,7 +514,8 @@ static struct core_reloc_test_case test_cases[] = {
 	},
 
 	/* validate we can find kernel module BTF types for relocs/attach */
-	MODULES_CASE("module", "raw_tp/bpf_testmod_test_read", "bpf_testmod_test_read"),
+	MODULES_CASE("module_probed", "raw_tp/bpf_testmod_test_read", "bpf_testmod_test_read"),
+	MODULES_CASE("module_direct", "tp_btf/bpf_testmod_test_read", NULL),
 
 	/* validate BPF program can use multiple flavors to match against
 	 * single target BTF type

tools/testing/selftests/bpf/progs/test_core_reloc_module.c

@@ -36,7 +36,7 @@ struct core_reloc_module_output {
 };
 
 SEC("raw_tp/bpf_testmod_test_read")
-int BPF_PROG(test_core_module,
+int BPF_PROG(test_core_module_probed,
 	     struct task_struct *task,
 	     struct bpf_testmod_test_read_ctx *read_ctx)
 {
@@ -64,3 +64,33 @@ int BPF_PROG(test_core_module,
 
 	return 0;
 }
+
+SEC("tp_btf/bpf_testmod_test_read")
+int BPF_PROG(test_core_module_direct,
+	     struct task_struct *task,
+	     struct bpf_testmod_test_read_ctx *read_ctx)
+{
+	struct core_reloc_module_output *out = (void *)&data.out;
+	__u64 pid_tgid = bpf_get_current_pid_tgid();
+	__u32 real_tgid = (__u32)(pid_tgid >> 32);
+	__u32 real_pid = (__u32)pid_tgid;
+
+	if (data.my_pid_tgid != pid_tgid)
+		return 0;
+
+	if (task->pid != real_pid || task->tgid != real_tgid)
+		return 0;
+
+	out->len = read_ctx->len;
+	out->off = read_ctx->off;
+
+	out->read_ctx_sz = bpf_core_type_size(struct bpf_testmod_test_read_ctx);
+	out->read_ctx_exists = bpf_core_type_exists(struct bpf_testmod_test_read_ctx);
+	out->buf_exists = bpf_core_field_exists(read_ctx->buf);
+	out->off_exists = bpf_core_field_exists(read_ctx->off);
+	out->len_exists = bpf_core_field_exists(read_ctx->len);
+
+	out->comm_len = BPF_CORE_READ_STR_INTO(&out->comm, task, comm);
+
+	return 0;
+}