selftests/bpf: Add test for __nullable suffix in tp_btf

Add a tracepoint with __nullable suffix in bpf_testmod, and add a
failure load case:

$./test_progs -t "module_attach"
 torvalds#173/1   module_attach/handle_tp_btf_nullable_bare:OK
 torvalds#173     module_attach:OK
 Summary: 1/1 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Philo Lu <lulie@linux.alibaba.com>

tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h

@@ -34,6 +34,12 @@ DECLARE_TRACE(bpf_testmod_test_write_bare,
 	TP_ARGS(task, ctx)
 );
 
+/* Used in bpf_testmod_test_read() to test __nullable suffix */
+DECLARE_TRACE(bpf_testmod_test_nullable_bare,
+	TP_PROTO(struct bpf_testmod_test_read_ctx *ctx__nullable),
+	TP_ARGS(ctx__nullable)
+);
+
 #undef BPF_TESTMOD_DECLARE_TRACE
 #ifdef DECLARE_TRACE_WRITABLE
 #define BPF_TESTMOD_DECLARE_TRACE(call, proto, args, size) \

tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c

@@ -394,6 +394,8 @@ bpf_testmod_test_read(struct file *file, struct kobject *kobj,
 	if (bpf_testmod_loop_test(101) > 100)
 		trace_bpf_testmod_test_read(current, &ctx);
 
+	trace_bpf_testmod_test_nullable_bare(NULL);
+
 	/* Magic number to enable writable tp */
 	if (len == 64) {
 		struct bpf_testmod_test_writable_ctx writable = {

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

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <test_progs.h>
+#include "test_tp_btf_nullable.skel.h"
+
+void test_tp_btf_nullable(void)
+{
+	if (env.has_testmod)
+		RUN_TESTS(test_tp_btf_nullable);
+	else
+		test__skip();
+}

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

@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include "../bpf_testmod/bpf_testmod.h"
+#include "bpf_misc.h"
+
+SEC("tp_btf/bpf_testmod_test_nullable_bare")
+__failure __msg("invalid mem access")
+int BPF_PROG(handle_tp_btf_nullable_bare1, struct bpf_testmod_test_read_ctx *nullable_ctx)
+{
+	return nullable_ctx->len;
+}
+
+SEC("tp_btf/bpf_testmod_test_nullable_bare")
+int BPF_PROG(handle_tp_btf_nullable_bare2, struct bpf_testmod_test_read_ctx *nullable_ctx)
+{
+	if (nullable_ctx)
+		return nullable_ctx->len;
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";