On Fri, Mar 26, 2021 at 03:38:30PM +0100, Christoph Hellwig wrote:

-static const char __user *get_user_arg_ptr(struct user_arg_ptr argv, int nr)
+static const char __user *
+get_user_arg_ptr(const char __user *const __user *argv, int nr)
 {
-	const char __user *native;
-
-#ifdef CONFIG_COMPAT
-	if (unlikely(argv.is_compat)) {
+	if (in_compat_syscall()) {
+		const compat_uptr_t __user *compat_argv =
+			compat_ptr((unsigned long)argv);
 		compat_uptr_t compat;
 
-		if (get_user(compat, argv.ptr.compat + nr))
+		if (get_user(compat, compat_argv + nr))
 			return ERR_PTR(-EFAULT);
-
 		return compat_ptr(compat);
-	}
-#endif
-
-	if (get_user(native, argv.ptr.native + nr))
-		return ERR_PTR(-EFAULT);
+	} else {
+		const char __user *native;
 
-	return native;
+		if (get_user(native, argv + nr))
+			return ERR_PTR(-EFAULT);
+		return native;
+	}
 }

Yecchhh....  So you have in_compat_syscall() called again and again, for
each argument in the list?  I agree that current version is fucking ugly,
but I really hate that approach ;-/