selftests/bpf: Add tests for get_func_[arg|ret|arg_cnt] helpers

Adding tests for get_func_[arg|ret|arg_cnt] helpers.
Using these helpers in fentry/fexit/fmod_ret programs.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211208193245.172141-6-jolsa@kernel.org

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

+// SPDX-License-Identifier: GPL-2.0
+#include <test_progs.h>
+#include "get_func_args_test.skel.h"
+
+void test_get_func_args_test(void)
+{
+	struct get_func_args_test *skel = NULL;
+	__u32 duration = 0, retval;
+	int err, prog_fd;
+
+	skel = get_func_args_test__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "get_func_args_test__open_and_load"))
+		return;
+
+	err = get_func_args_test__attach(skel);
+	if (!ASSERT_OK(err, "get_func_args_test__attach"))
+		goto cleanup;
+
+	/* This runs bpf_fentry_test* functions and triggers
+	 * fentry/fexit programs.
+	 */
+	prog_fd = bpf_program__fd(skel->progs.test1);
+	err = bpf_prog_test_run(prog_fd, 1, NULL, 0,
+				NULL, NULL, &retval, &duration);
+	ASSERT_OK(err, "test_run");
+	ASSERT_EQ(retval, 0, "test_run");
+
+	/* This runs bpf_modify_return_test function and triggers
+	 * fmod_ret_test and fexit_test programs.
+	 */
+	prog_fd = bpf_program__fd(skel->progs.fmod_ret_test);
+	err = bpf_prog_test_run(prog_fd, 1, NULL, 0,
+				NULL, NULL, &retval, &duration);
+	ASSERT_OK(err, "test_run");
+	ASSERT_EQ(retval, 1234, "test_run");
+
+	ASSERT_EQ(skel->bss->test1_result, 1, "test1_result");
+	ASSERT_EQ(skel->bss->test2_result, 1, "test2_result");
+	ASSERT_EQ(skel->bss->test3_result, 1, "test3_result");
+	ASSERT_EQ(skel->bss->test4_result, 1, "test4_result");
+
+cleanup:
+	get_func_args_test__destroy(skel);
+}

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

+// SPDX-License-Identifier: GPL-2.0
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include <errno.h>
+
+char _license[] SEC("license") = "GPL";
+
+__u64 test1_result = 0;
+SEC("fentry/bpf_fentry_test1")
+int BPF_PROG(test1)
+{
+	__u64 cnt = bpf_get_func_arg_cnt(ctx);
+	__u64 a = 0, z = 0, ret = 0;
+	__s64 err;
+
+	test1_result = cnt == 1;
+
+	/* valid arguments */
+	err = bpf_get_func_arg(ctx, 0, &a);
+
+	/* We need to cast access to traced function argument values with
+	 * proper type cast, because trampoline uses type specific instruction
+	 * to save it, like for 'int a' with 32-bit mov like:
+	 *
+	 *   mov %edi,-0x8(%rbp)
+	 *
+	 * so the upper 4 bytes are not zeroed.
+	 */
+	test1_result &= err == 0 && ((int) a == 1);
+
+	/* not valid argument */
+	err = bpf_get_func_arg(ctx, 1, &z);
+	test1_result &= err == -EINVAL;
+
+	/* return value fails in fentry */
+	err = bpf_get_func_ret(ctx, &ret);
+	test1_result &= err == -EOPNOTSUPP;
+	return 0;
+}
+
+__u64 test2_result = 0;
+SEC("fexit/bpf_fentry_test2")
+int BPF_PROG(test2)
+{
+	__u64 cnt = bpf_get_func_arg_cnt(ctx);
+	__u64 a = 0, b = 0, z = 0, ret = 0;
+	__s64 err;
+
+	test2_result = cnt == 2;
+
+	/* valid arguments */
+	err = bpf_get_func_arg(ctx, 0, &a);
+	test2_result &= err == 0 && (int) a == 2;
+
+	err = bpf_get_func_arg(ctx, 1, &b);
+	test2_result &= err == 0 && b == 3;
+
+	/* not valid argument */
+	err = bpf_get_func_arg(ctx, 2, &z);
+	test2_result &= err == -EINVAL;
+
+	/* return value */
+	err = bpf_get_func_ret(ctx, &ret);
+	test2_result &= err == 0 && ret == 5;
+	return 0;
+}
+
+__u64 test3_result = 0;
+SEC("fmod_ret/bpf_modify_return_test")
+int BPF_PROG(fmod_ret_test, int _a, int *_b, int _ret)
+{
+	__u64 cnt = bpf_get_func_arg_cnt(ctx);
+	__u64 a = 0, b = 0, z = 0, ret = 0;
+	__s64 err;
+
+	test3_result = cnt == 2;
+
+	/* valid arguments */
+	err = bpf_get_func_arg(ctx, 0, &a);
+	test3_result &= err == 0 && ((int) a == 1);
+
+	err = bpf_get_func_arg(ctx, 1, &b);
+	test3_result &= err == 0 && ((int *) b == _b);
+
+	/* not valid argument */
+	err = bpf_get_func_arg(ctx, 2, &z);
+	test3_result &= err == -EINVAL;
+
+	/* return value */
+	err = bpf_get_func_ret(ctx, &ret);
+	test3_result &= err == 0 && ret == 0;
+
+	/* change return value, it's checked in fexit_test program */
+	return 1234;
+}
+
+__u64 test4_result = 0;
+SEC("fexit/bpf_modify_return_test")
+int BPF_PROG(fexit_test, int _a, int *_b, int _ret)
+{
+	__u64 cnt = bpf_get_func_arg_cnt(ctx);
+	__u64 a = 0, b = 0, z = 0, ret = 0;
+	__s64 err;
+
+	test4_result = cnt == 2;
+
+	/* valid arguments */
+	err = bpf_get_func_arg(ctx, 0, &a);
+	test4_result &= err == 0 && ((int) a == 1);
+
+	err = bpf_get_func_arg(ctx, 1, &b);
+	test4_result &= err == 0 && ((int *) b == _b);
+
+	/* not valid argument */
+	err = bpf_get_func_arg(ctx, 2, &z);
+	test4_result &= err == -EINVAL;
+
+	/* return value */
+	err = bpf_get_func_ret(ctx, &ret);
+	test4_result &= err == 0 && ret == 1234;
+	return 0;
+}