From: david.laight.linux@gmail•com
To: Alexander Viro <viro@zeniv•linux.org.uk>,
Andre Almeida <andrealmeid@igalia•com>,
Andrew Cooper <andrew.cooper3@citrix•com>,
Christian Borntraeger <borntraeger@linux•ibm.com>,
Christian Brauner <brauner@kernel•org>,
Christophe Leroy <christophe.leroy@csgroup•eu>,
"Christophe Leroy (CS GROUP)" <chleroy@kernel•org>,
Darren Hart <dvhart@infradead•org>,
David Laight <david.laight.linux@gmail•com>,
Davidlohr Bueso <dave@stgolabs•net>,
Heiko Carstens <hca@linux•ibm.com>, Jan Kara <jack@suse•cz>,
Julia Lawall <Julia.Lawall@inria•fr>,
Linus Torvalds <torvalds@linux-foundation•org>,
linux-arm-kernel@lists•infradead.org,
linux-fsdevel@vger•kernel.org, linuxppc-dev@lists•ozlabs.org,
linux-riscv@lists•infradead.org, linux-s390@vger•kernel.org,
LKML <linux-kernel@vger•kernel.org>,
Madhavan Srinivasan <maddy@linux•ibm.com>,
Mathieu Desnoyers <mathieu.desnoyers@efficios•com>,
Michael Ellerman <mpe@ellerman•id.au>,
Nicholas Piggin <npiggin@gmail•com>,
Nicolas Palix <nicolas.palix@imag•fr>,
Palmer Dabbelt <palmer@dabbelt•com>,
Paul Walmsley <pjw@kernel•org>,
Peter Zijlstra <peterz@infradead•org>,
Russell King <linux@armlinux•org.uk>,
Sven Schnelle <svens@linux•ibm.com>,
Thomas Gleixner <tglx@linutronix•de>,
x86@kernel•org, Kees Cook <kees@kernel•org>,
akpm@linux-foundation•org
Subject: [PATCH v2 2/5] compiler.h: Add generic support for 'autoterminating nested for() loops'
Date: Mon, 2 Mar 2026 13:27:52 +0000 [thread overview]
Message-ID: <20260302132755.1475451-3-david.laight.linux@gmail.com> (raw)
In-Reply-To: <20260302132755.1475451-1-david.laight.linux@gmail.com>
From: David Laight <david.laight.linux@gmail•com>
Autoterminating nested for() loops can be used inside #defines to
declare variables that are scoped to the statement that follows.
These are used by __scoped_user_access() but may have other uses
and the gory details are best separated from the use.
Using 'with (declaration)' and 'and_with (declaration)' seems to
read reasonably well and doesn't seem to collide with any existing
code.
As an example the scoped user access definition becomes:
with (auto _tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl)) \
/* Force modified pointer usage within the scope */ \
and_with (const auto uptr __cleanup(...) = _tmpptr)
Signed-off-by: David Laight <david.laight.linux@gmail•com>
---
include/linux/compiler.h | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index af16624b29fd..1098a91b5591 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -369,6 +369,32 @@ static inline void *offset_to_ptr(const int *off)
*/
#define prevent_tail_call_optimization() mb()
+/*
+ * 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(x, 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 return, 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)
+
#include <asm/rwonce.h>
#endif /* __LINUX_COMPILER_H */
--
2.39.5
next prev parent reply other threads:[~2026-03-02 14:10 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-02 13:27 [PATCH v2 0/5] uaccess: Updates to scoped_user_access() david.laight.linux
2026-03-02 13:27 ` [PATCH v2 1/5] uaccess: Fix scoped_user_read_access() for 'pointer to const' david.laight.linux
2026-03-02 14:59 ` Christophe Leroy (CS GROUP)
2026-03-02 17:26 ` Linus Torvalds
2026-03-02 18:55 ` David Laight
2026-03-02 13:27 ` david.laight.linux [this message]
2026-03-02 13:27 ` [PATCH v2 3/5] uaccess.h: Use with() and and_with() in __scoped_user_access() david.laight.linux
2026-03-02 13:27 ` [PATCH v2 4/5] uaccess: Disable -Wshadow " david.laight.linux
2026-03-02 15:00 ` Christophe Leroy (CS GROUP)
2026-03-03 9:12 ` David Laight
2026-03-02 17:17 ` Linus Torvalds
2026-03-05 8:10 ` kernel test robot
2026-03-02 13:27 ` [PATCH v2 next 5/5] signal: Use scoped_user_access() instead of __put/get_user() david.laight.linux
2026-03-02 16:07 ` Christophe Leroy (CS GROUP)
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