linux-kernel - [PATCH v2 3/8] compiler.h: Add __if_constexpr(expr, if_const, if_not

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <2e12aefe29884e578283129411e1df26@AcuMS.aculab.com>
Date: Sun, 28 Jul 2024 14:19:52 +0000
From: David Laight <David.Laight@...LAB.COM>
To: "'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>
CC: 'Linus Torvalds' <torvalds@...uxfoundation.org>, 'Jens Axboe'
	<axboe@...nel.dk>, "'Matthew Wilcox (Oracle)'" <willy@...radead.org>,
	'Christoph Hellwig' <hch@...radead.org>, 'Andrew Morton'
	<akpm@...ux-foundation.org>, 'Andy Shevchenko'
	<andriy.shevchenko@...ux.intel.com>, 'Dan Carpenter'
	<dan.carpenter@...aro.org>, 'Arnd Bergmann' <arnd@...nel.org>,
	"'Jason@...c4.com'" <Jason@...c4.com>, "'pedro.falcato@...il.com'"
	<pedro.falcato@...il.com>, 'Mateusz Guzik' <mjguzik@...il.com>,
	"'linux-mm@...ck.org'" <linux-mm@...ck.org>, 'Lorenzo Stoakes'
	<lorenzo.stoakes@...cle.com>
Subject: [PATCH v2 3/8] compiler.h: Add __if_constexpr(expr, if_const,
 if_not_const)

__if_constexpr(expr, if_const, if_not_const) returns 'if_const' if 'expr'
is a 'constant integer expression' otherwise 'if_not_const'.
The two values may have different types.

__is_constexpr(expr) is equivalent to __if_constexpr(expr, 1, 0).

Signed-off-by: David Laight <david.laight@...lab.com>
---
v2:
- Don't change __is_constexpr()

 include/linux/compiler.h | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 2594553bb30b..35d5b2fa4786 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -242,6 +242,23 @@ static inline void *offset_to_ptr(const int *off)
 /* &a[0] degrades to a pointer: a different type from an array */
 #define __must_be_array(a)	BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
 
+/**
+ * __if_constexpr - Check whether an expression is an 'integer
+ *		constant expression'
+ * @expr: Expression to test, not evaluated, can be a pointer
+ * @if_const: return value if constant
+ * @if_not_const: return value if not constant
+ *
+ * The return values @if_const and @if_not_const can have different types.
+ *
+ * Relies on typeof(x ? NULL : ptr_type) being ptr_type and
+ * typeof(x ? (void *)y : ptr_type) being 'void *'.
+ */
+#define __if_constexpr(expr, if_const, if_not_const)		\
+       _Generic(0 ? ((void *)((long)(expr) * 0l)) : (char *)0,	\
+		char *: (if_const),				\
+		void *: (if_not_const))
+
 /*
  * This returns a constant expression while determining if an argument is
  * a constant expression, most importantly without evaluating the argument.
-- 
2.17.1

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)