selftests/bpf: Add type match test against kernel's task_struct

This change extends the existing core_reloc/kernel test to include a
type match check of a local task_struct against the kernel's definition
-- which we assume to succeed.
Signed-off-by: Daniel Müller <deso@posteo.net>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220628160127.607834-11-deso@posteo.net

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

@@ -555,6 +555,7 @@ static const struct core_reloc_test_case test_cases[] = {
 			.valid = { 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, },
 			.comm = "test_progs",
 			.comm_len = sizeof("test_progs"),
+			.local_task_struct_matches = true,
 		},
 		.output_len = sizeof(struct core_reloc_kernel_output),
 		.raw_tp_name = "sys_enter",

tools/testing/selftests/bpf/progs/core_reloc_types.h

@@ -13,6 +13,7 @@ struct core_reloc_kernel_output {
 	int valid[10];
 	char comm[sizeof("test_progs")];
 	int comm_len;
+	bool local_task_struct_matches;
 };
 
 /*

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

@@ -21,6 +21,7 @@ struct core_reloc_kernel_output {
 	/* we have test_progs[-flavor], so cut flavor part */
 	char comm[sizeof("test_progs")];
 	int comm_len;
+	bool local_task_struct_matches;
 };
 
 struct task_struct {
@@ -30,11 +31,25 @@ struct task_struct {
 	struct task_struct *group_leader;
 };
 
+struct mm_struct___wrong {
+    int abc_whatever_should_not_exist;
+};
+
+struct task_struct___local {
+    int pid;
+    struct mm_struct___wrong *mm;
+};
+
 #define CORE_READ(dst, src) bpf_core_read(dst, sizeof(*(dst)), src)
 
 SEC("raw_tracepoint/sys_enter")
 int test_core_kernel(void *ctx)
 {
+	/* Support for the BPF_TYPE_MATCHES argument to the
+	 * __builtin_preserve_type_info builtin was added at some point during
+	 * development of clang 15 and it's what we require for this test.
+	 */
+#if __has_builtin(__builtin_preserve_type_info) && __clang_major__ >= 15
 	struct task_struct *task = (void *)bpf_get_current_task();
 	struct core_reloc_kernel_output *out = (void *)&data.out;
 	uint64_t pid_tgid = bpf_get_current_pid_tgid();
@@ -93,6 +108,10 @@ int test_core_kernel(void *ctx)
 		group_leader, group_leader, group_leader, group_leader,
 		comm);
 
+	out->local_task_struct_matches = bpf_core_type_matches(struct task_struct___local);
+#else
+	data.skip = true;
+#endif
 	return 0;
 }