v4.19.13 snapshot.
diff --git a/arch/arm64/kernel/sys_compat.c b/arch/arm64/kernel/sys_compat.c
new file mode 100644
index 0000000..a610982
--- /dev/null
+++ b/arch/arm64/kernel/sys_compat.c
@@ -0,0 +1,124 @@
+/*
+ * Based on arch/arm/kernel/sys_arm.c
+ *
+ * Copyright (C) People who wrote linux/arch/i386/kernel/sys_i386.c
+ * Copyright (C) 1995, 1996 Russell King.
+ * Copyright (C) 2012 ARM Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/compat.h>
+#include <linux/personality.h>
+#include <linux/sched.h>
+#include <linux/sched/signal.h>
+#include <linux/slab.h>
+#include <linux/syscalls.h>
+#include <linux/uaccess.h>
+
+#include <asm/cacheflush.h>
+#include <asm/system_misc.h>
+#include <asm/unistd.h>
+
+static long
+__do_compat_cache_op(unsigned long start, unsigned long end)
+{
+ long ret;
+
+ do {
+ unsigned long chunk = min(PAGE_SIZE, end - start);
+
+ if (fatal_signal_pending(current))
+ return 0;
+
+ ret = __flush_cache_user_range(start, start + chunk);
+ if (ret)
+ return ret;
+
+ cond_resched();
+ start += chunk;
+ } while (start < end);
+
+ return 0;
+}
+
+static inline long
+do_compat_cache_op(unsigned long start, unsigned long end, int flags)
+{
+ if (end < start || flags)
+ return -EINVAL;
+
+ if (!access_ok(VERIFY_READ, (const void __user *)start, end - start))
+ return -EFAULT;
+
+ return __do_compat_cache_op(start, end);
+}
+/*
+ * Handle all unrecognised system calls.
+ */
+long compat_arm_syscall(struct pt_regs *regs)
+{
+ siginfo_t info;
+ unsigned int no = regs->regs[7];
+
+ switch (no) {
+ /*
+ * Flush a region from virtual address 'r0' to virtual address 'r1'
+ * _exclusive_. There is no alignment requirement on either address;
+ * user space does not need to know the hardware cache layout.
+ *
+ * r2 contains flags. It should ALWAYS be passed as ZERO until it
+ * is defined to be something else. For now we ignore it, but may
+ * the fires of hell burn in your belly if you break this rule. ;)
+ *
+ * (at a later date, we may want to allow this call to not flush
+ * various aspects of the cache. Passing '0' will guarantee that
+ * everything necessary gets flushed to maintain consistency in
+ * the specified region).
+ */
+ case __ARM_NR_compat_cacheflush:
+ return do_compat_cache_op(regs->regs[0], regs->regs[1], regs->regs[2]);
+
+ case __ARM_NR_compat_set_tls:
+ current->thread.uw.tp_value = regs->regs[0];
+
+ /*
+ * Protect against register corruption from context switch.
+ * See comment in tls_thread_flush.
+ */
+ barrier();
+ write_sysreg(regs->regs[0], tpidrro_el0);
+ return 0;
+
+ default:
+ /*
+ * Calls 9f00xx..9f07ff are defined to return -ENOSYS
+ * if not implemented, rather than raising SIGILL. This
+ * way the calling program can gracefully determine whether
+ * a feature is supported.
+ */
+ if ((no & 0xffff) <= 0x7ff)
+ return -ENOSYS;
+ break;
+ }
+
+ clear_siginfo(&info);
+ info.si_signo = SIGILL;
+ info.si_errno = 0;
+ info.si_code = ILL_ILLTRP;
+ info.si_addr = (void __user *)instruction_pointer(regs) -
+ (compat_thumb_mode(regs) ? 2 : 4);
+
+ arm64_notify_die("Oops - bad compat syscall(2)", regs, &info, no);
+ return 0;
+}