Subject: Re: [PATCH] uaccess: Fix build of scoped user access with const pointer

From: David Laight <[email-masked]>
Date: Sun, 1 Mar 2026 22:16:36 +0000

On Sun, 1 Mar 2026 12:01:08 -0800
Linus Torvalds <[email-masked]> wrote:

I also added to compiler.h :

+/*
+ * Sometimes a #define needs to declare a variable that is scoped
+ * to the statement that follows without having mismatched {}.
+ *	with (int x = expression) {
+ *		statements
+ *	}
+ * is the same as:
+ *	{
+ *		int x = expression;
+ *		statements
+ *	}
+ * but lets it all be hidden from the call site, eg:
+ *	frobnicate(args) {
+ *		statements
+ *	} 
+ * Only a single variable can be defined, and_with() allows extra ones
+ * without adding an additional outer loop.
+ *
+ * The controlled scope can be terminated using break, continue or goto.
+ */
+#define with(declaration) \
+	for (bool _with_done = false; !_with_done; _with_done = true)	\
+		and_with (declaration)
+#define and_with(declaration) \
+	for (declaration; !_with_done; _with_done = true)
+

So that you get:
#define __scoped_user_access(mode, uptr, size, elbl)					\
	with (auto _tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl)) \
		and_with (CLASS(user_##mode##_access, scope)(_tmpptr))			\
		/* Force modified pointer usage within the scope */			\
		and_with (const auto uptr = _tmpptr)

The next patch did:
-		and_with (const typeof(uptr) uptr = _tmpptr)
+		__diag_push() __diag_ignore_all("-Wshadow", "uptr is readonly copy")	\
+		and_with (const typeof(uptr) uptr = _tmpptr)				\
+		__diag_pop()

I'll update (to use auto as above) and resend.

	David