The test creates two processes where one traces another one.  The tracee
executes a system call, the tracer traps it, changes orig_x0, triggers a
signal and checks that the syscall is restarted with the setted
argument.

Test output:
 $ ./ptrace_restart_syscall_test
 1..3
 ok 1 orig_x0: 0x3
 ok 2 x0: 0x5
 ok 3 The child exited with code 0.
 # Totals: pass:3 fail:0 xfail:0 xpass:0 skip:0 error:0

Signed-off-by: Andrei Vagin <ava...@gmail.com>
---
 tools/testing/selftests/arm64/ptrace/Makefile |   6 +
 tools/testing/selftests/arm64/ptrace/lib.h    |  36 ++++++
 .../ptrace/ptrace_restart_syscall_test.c      | 122 ++++++++++++++++++
 3 files changed, 164 insertions(+)
 create mode 100644 tools/testing/selftests/arm64/ptrace/Makefile
 create mode 100644 tools/testing/selftests/arm64/ptrace/lib.h
 create mode 100644 
tools/testing/selftests/arm64/ptrace/ptrace_restart_syscall_test.c

diff --git a/tools/testing/selftests/arm64/ptrace/Makefile 
b/tools/testing/selftests/arm64/ptrace/Makefile
new file mode 100644
index 000000000000..1bc10e2d2ac8
--- /dev/null
+++ b/tools/testing/selftests/arm64/ptrace/Makefile
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
+
+CFLAGS += -g -I../../../../../usr/include/
+TEST_GEN_PROGS := ptrace_restart_syscall_test
+
+include ../../lib.mk
diff --git a/tools/testing/selftests/arm64/ptrace/lib.h 
b/tools/testing/selftests/arm64/ptrace/lib.h
new file mode 100644
index 000000000000..14f4737188a3
--- /dev/null
+++ b/tools/testing/selftests/arm64/ptrace/lib.h
@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#ifndef __PTRACE_TEST_LOG_H
+#define __PTRACE_TEST_LOG_H
+
+#define pr_p(func, fmt, ...) func("%s:%d: " fmt ": %m", \
+                                 __func__, __LINE__, ##__VA_ARGS__)
+
+#define pr_err(fmt, ...)                                               \
+       ({                                                              \
+               ksft_test_result_error(fmt "\n", ##__VA_ARGS__);        \
+               -1;                                                     \
+       })
+
+#define pr_fail(fmt, ...)                                      \
+       ({                                                      \
+               ksft_test_result_fail(fmt "\n", ##__VA_ARGS__); \
+               -1;                                             \
+       })
+
+#define pr_perror(fmt, ...)    pr_p(pr_err, fmt, ##__VA_ARGS__)
+
+static inline int ptrace_and_wait(pid_t pid, int cmd, int sig)
+{
+       int status;
+
+       /* Stop on syscall-exit. */
+       if (ptrace(cmd, pid, 0, 0))
+               return pr_perror("Can't resume the child %d", pid);
+       if (waitpid(pid, &status, 0) != pid)
+               return pr_perror("Can't wait for the child %d", pid);
+       if (!WIFSTOPPED(status) || WSTOPSIG(status) != sig)
+               return pr_err("Unexpected status: %x", status);
+       return 0;
+}
+
+#endif
diff --git a/tools/testing/selftests/arm64/ptrace/ptrace_restart_syscall_test.c 
b/tools/testing/selftests/arm64/ptrace/ptrace_restart_syscall_test.c
new file mode 100644
index 000000000000..ce59657f41be
--- /dev/null
+++ b/tools/testing/selftests/arm64/ptrace/ptrace_restart_syscall_test.c
@@ -0,0 +1,122 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <errno.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <fcntl.h>
+
+#include <sys/types.h>
+#include <sys/ptrace.h>
+#include <sys/stat.h>
+#include <sys/user.h>
+#include <sys/wait.h>
+#include <sys/uio.h>
+#include <linux/elf.h>
+#include <linux/unistd.h>
+
+#include "../../kselftest.h"
+#include "lib.h"
+
+static int child(int fd)
+{
+       char c;
+
+       if (read(fd, &c, 1) != 1)
+               return 1;
+
+       return 0;
+}
+
+int main(int argc, void **argv)
+{
+       union {
+               struct user_regs_struct r;
+               struct {
+                       char __regs[272];
+                       unsigned long long orig_x0;
+                       unsigned long long orig_x7;
+               };
+       } regs = {};
+       struct iovec iov = {
+               .iov_base = &regs,
+               .iov_len = sizeof(regs),
+       };
+       int status;
+       pid_t pid;
+       int p[2], fdzero;
+
+       ksft_set_plan(3);
+
+       if (pipe(p))
+               return pr_perror("Can't create a pipe");
+       fdzero = open("/dev/zero", O_RDONLY);
+       if (fdzero < 0)
+               return pr_perror("Can't open /dev/zero");
+
+       pid = fork();
+       if (pid == 0) {
+               kill(getpid(), SIGSTOP);
+               return child(p[0]);
+       }
+       if (pid < 0)
+               return 1;
+
+       if (ptrace(PTRACE_ATTACH, pid, 0, 0))
+               return pr_perror("Can't attach to the child %d", pid);
+       if (waitpid(pid, &status, 0) != pid)
+               return pr_perror("Can't wait for the child %d", pid);
+       /* Skip SIGSTOP */
+       if (ptrace_and_wait(pid, PTRACE_CONT, SIGSTOP))
+               return 1;
+
+       /* Resume the child to the next system call. */
+       if (ptrace_and_wait(pid, PTRACE_SYSCALL, SIGTRAP))
+               return 1;
+
+       /* Send a signal to interrupt the system call. */
+       kill(pid, SIGUSR1);
+
+       /* Stop on syscall-exit. */
+       if (ptrace_and_wait(pid, PTRACE_SYSCALL, SIGTRAP))
+               return 1;
+
+       if (ptrace(PTRACE_GETREGSET, pid, NT_PRSTATUS, &iov))
+               return pr_perror("Can't get child registers");
+       if (regs.orig_x0 != p[0])
+               return pr_fail("Unexpected x0: 0x%lx", regs.r.regs[0]);
+       ksft_test_result_pass("orig_x0: 0x%llx\n", regs.orig_x0);
+
+       /* Change orig_x0 that will be x0 for the restarted system call. */
+       regs.orig_x0 = fdzero;
+       if (ptrace(PTRACE_SETREGSET, pid, NT_PRSTATUS, &iov))
+               return pr_perror("Can't get child registers");
+
+       /* Trap the signal and skip it. */
+       if (ptrace_and_wait(pid, PTRACE_SYSCALL, SIGUSR1))
+               return 1;
+
+       /* Trap the restarted system call. */
+       if (ptrace_and_wait(pid, PTRACE_SYSCALL, SIGTRAP))
+               return 1;
+
+       /* Check that the syscall is started with the right first argument. */
+       if (ptrace(PTRACE_GETREGSET, pid, NT_PRSTATUS, &iov))
+               return pr_perror("Can't get child registers");
+       if (regs.r.regs[0] != fdzero)
+               return pr_fail("unexpected x0: %lx", regs.r.regs[0]);
+       ksft_test_result_pass("x0: 0x%llx\n", regs.r.regs[0]);
+
+       if (ptrace(PTRACE_CONT, pid, 0, 0))
+               return pr_perror("Can't resume the child %d", pid);
+       if (waitpid(pid, &status, 0) != pid)
+               return pr_perror("Can't wait for the child %d", pid);
+       if (status != 0)
+               return pr_fail("Child exited with code %d.", status);
+
+       ksft_test_result_pass("The child exited with code 0.\n");
+       ksft_exit_pass();
+       return 0;
+}
+
-- 
2.29.2

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