selftests/bpf: Add 6-argument syscall tracing test

Turns out splice() is one of the syscalls that's using current maximum
number of arguments (six). This is perfect for testing, so extend
bpf_syscall_macro selftest to also trace splice() syscall, using
BPF_KSYSCALL() macro. This makes sure all the syscall argument register
definitions are correct.
Suggested-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Alan Maguire <alan.maguire@oracle.com> # arm64
Tested-by: Ilya Leoshkevich <iii@linux.ibm.com> # s390x
Link: https://lore.kernel.org/bpf/20230120200914.3008030-25-andrii@kernel.org

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

 // SPDX-License-Identifier: GPL-2.0
 /* Copyright 2022 Sony Group Corporation */
+#define _GNU_SOURCE
+#include <fcntl.h>
 #include <sys/prctl.h>
 #include <test_progs.h>
 #include "bpf_syscall_macro.skel.h"
@@ -13,6 +15,8 @@ void test_bpf_syscall_macro(void)
 	unsigned long exp_arg3 = 13;
 	unsigned long exp_arg4 = 14;
 	unsigned long exp_arg5 = 15;
+	loff_t off_in, off_out;
+	ssize_t r;
 
 	/* check whether it can open program */
 	skel = bpf_syscall_macro__open();
@@ -33,6 +37,7 @@ void test_bpf_syscall_macro(void)
 
 	/* check whether args of syscall are copied correctly */
 	prctl(exp_arg1, exp_arg2, exp_arg3, exp_arg4, exp_arg5);
+
 #if defined(__aarch64__) || defined(__s390__)
 	ASSERT_NEQ(skel->bss->arg1, exp_arg1, "syscall_arg1");
 #else
@@ -68,6 +73,18 @@ void test_bpf_syscall_macro(void)
 	ASSERT_EQ(skel->bss->arg4_syscall, exp_arg4, "BPF_KPROBE_SYSCALL_arg4");
 	ASSERT_EQ(skel->bss->arg5_syscall, exp_arg5, "BPF_KPROBE_SYSCALL_arg5");
 
+	r = splice(-42, &off_in, 42, &off_out, 0x12340000, SPLICE_F_NONBLOCK);
+	err = -errno;
+	ASSERT_EQ(r, -1, "splice_res");
+	ASSERT_EQ(err, -EBADF, "splice_err");
+
+	ASSERT_EQ(skel->bss->splice_fd_in, -42, "splice_arg1");
+	ASSERT_EQ(skel->bss->splice_off_in, (__u64)&off_in, "splice_arg2");
+	ASSERT_EQ(skel->bss->splice_fd_out, 42, "splice_arg3");
+	ASSERT_EQ(skel->bss->splice_off_out, (__u64)&off_out, "splice_arg4");
+	ASSERT_EQ(skel->bss->splice_len, 0x12340000, "splice_arg5");
+	ASSERT_EQ(skel->bss->splice_flags, SPLICE_F_NONBLOCK, "splice_arg6");
+
 cleanup:
 	bpf_syscall_macro__destroy(skel);
 }

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

@@ -81,4 +81,30 @@ int BPF_KSYSCALL(prctl_enter, int option, unsigned long arg2,
 	return 0;
 }
 
+__u64 splice_fd_in;
+__u64 splice_off_in;
+__u64 splice_fd_out;
+__u64 splice_off_out;
+__u64 splice_len;
+__u64 splice_flags;
+
+SEC("ksyscall/splice")
+int BPF_KSYSCALL(splice_enter, int fd_in, loff_t *off_in, int fd_out,
+		 loff_t *off_out, size_t len, unsigned int flags)
+{
+	pid_t pid = bpf_get_current_pid_tgid() >> 32;
+
+	if (pid != filter_pid)
+		return 0;
+
+	splice_fd_in = fd_in;
+	splice_off_in = (__u64)off_in;
+	splice_fd_out = fd_out;
+	splice_off_out = (__u64)off_out;
+	splice_len = len;
+	splice_flags = flags;
+
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";