[PATCHv3 09/19] arm64: convert syscall trace logic to C

On Mon, Jun 18, 2018 at 01:03:00PM +0100, Mark Rutland wrote:

+asmlinkage void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
+			       syscall_fn_t syscall_table[])
+{
+	unsigned long flags = current_thread_info()->flags;
+
+	regs->orig_x0 = regs->regs[0];
+	regs->syscallno = scno;
+
+	local_daif_restore(DAIF_PROCCTX);
+	user_exit();
+
+	if (has_syscall_work(flags)) {
+		/* set default errno for user-issued syscall(-1) */
+		if (scno == NO_SYSCALL)
+			regs->regs[0] = -ENOSYS;
+		scno = syscall_trace_enter(regs);
+		if (scno == NO_SYSCALL)
+			goto trace_exit;
+	}
+
+	invoke_syscall(regs, scno, sc_nr, syscall_table);
+
+	/*
+	 * The tracing status may have changed under our feet, so we have to
+	 * check again. However, if we were tracing entry, then we always trace
+	 * exit regardless, as the old entry assembly did.
+	 */
+	if (!has_syscall_work(flags)) {
+		local_daif_mask();
+		flags = current_thread_info()->flags;
+		if (!has_syscall_work(flags))
+			return;
+		local_daif_restore(DAIF_PROCCTX);
+	}

IIUC the above 'if' block replaces ret_fast_syscall in entry.S with the
work_pending handled via ret_to_user (we used to check _TIF_WORK_MASK in
two places). 

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>