v4.19.13 snapshot.
diff --git a/lib/syscall.c b/lib/syscall.c
new file mode 100644
index 0000000..1a7077f
--- /dev/null
+++ b/lib/syscall.c
@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/ptrace.h>
+#include <linux/sched.h>
+#include <linux/sched/task_stack.h>
+#include <linux/export.h>
+#include <asm/syscall.h>
+
+static int collect_syscall(struct task_struct *target, long *callno,
+ unsigned long args[6], unsigned int maxargs,
+ unsigned long *sp, unsigned long *pc)
+{
+ struct pt_regs *regs;
+
+ if (!try_get_task_stack(target)) {
+ /* Task has no stack, so the task isn't in a syscall. */
+ *sp = *pc = 0;
+ *callno = -1;
+ return 0;
+ }
+
+ regs = task_pt_regs(target);
+ if (unlikely(!regs)) {
+ put_task_stack(target);
+ return -EAGAIN;
+ }
+
+ *sp = user_stack_pointer(regs);
+ *pc = instruction_pointer(regs);
+
+ *callno = syscall_get_nr(target, regs);
+ if (*callno != -1L && maxargs > 0)
+ syscall_get_arguments(target, regs, 0, maxargs, args);
+
+ put_task_stack(target);
+ return 0;
+}
+
+/**
+ * task_current_syscall - Discover what a blocked task is doing.
+ * @target: thread to examine
+ * @callno: filled with system call number or -1
+ * @args: filled with @maxargs system call arguments
+ * @maxargs: number of elements in @args to fill
+ * @sp: filled with user stack pointer
+ * @pc: filled with user PC
+ *
+ * If @target is blocked in a system call, returns zero with *@callno
+ * set to the the call's number and @args filled in with its arguments.
+ * Registers not used for system call arguments may not be available and
+ * it is not kosher to use &struct user_regset calls while the system
+ * call is still in progress. Note we may get this result if @target
+ * has finished its system call but not yet returned to user mode, such
+ * as when it's stopped for signal handling or syscall exit tracing.
+ *
+ * If @target is blocked in the kernel during a fault or exception,
+ * returns zero with *@callno set to -1 and does not fill in @args.
+ * If so, it's now safe to examine @target using &struct user_regset
+ * get() calls as long as we're sure @target won't return to user mode.
+ *
+ * Returns -%EAGAIN if @target does not remain blocked.
+ *
+ * Returns -%EINVAL if @maxargs is too large (maximum is six).
+ */
+int task_current_syscall(struct task_struct *target, long *callno,
+ unsigned long args[6], unsigned int maxargs,
+ unsigned long *sp, unsigned long *pc)
+{
+ long state;
+ unsigned long ncsw;
+
+ if (unlikely(maxargs > 6))
+ return -EINVAL;
+
+ if (target == current)
+ return collect_syscall(target, callno, args, maxargs, sp, pc);
+
+ state = target->state;
+ if (unlikely(!state))
+ return -EAGAIN;
+
+ ncsw = wait_task_inactive(target, state);
+ if (unlikely(!ncsw) ||
+ unlikely(collect_syscall(target, callno, args, maxargs, sp, pc)) ||
+ unlikely(wait_task_inactive(target, state) != ncsw))
+ return -EAGAIN;
+
+ return 0;
+}