Cloning the similar construct from Linux, allowing to detect improper
uses of ARRAY_SIZE() at build time.
Signed-off-by: Jan Beulich <jbeulich@novell.com>
--- 2009-03-27.orig/xen/include/xen/compiler.h 2008-06-10 18:00:41.000000000
+0200
+++ 2009-03-27/xen/include/xen/compiler.h 2009-04-07 13:38:22.000000000 +0200
@@ -35,6 +35,10 @@
#define offsetof(a,b) ((unsigned long)&(((a *)0)->b))
#endif
+/* &a[0] degrades to a pointer: a different type from an array */
+#define __must_be_array(a) \
+ BUILD_BUG_ON_ZERO(__builtin_types_compatible_p(typeof(a), typeof(&a[0])))
+
#ifdef GCC_HAS_VISIBILITY_ATTRIBUTE
/* Results in more efficient PIC code (no indirections through GOT or PLT). */
#pragma GCC visibility push(hidden)
--- 2009-03-27.orig/xen/include/xen/config.h 2007-10-12 16:12:16.000000000 +0200
+++ 2009-03-27/xen/include/xen/config.h 2009-04-07 13:41:00.000000000 +0200
@@ -11,7 +11,7 @@
#define EXPORT_SYMBOL(var)
#define EXPORT_SYMBOL_GPL(var)
-#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]) + __must_be_array(x))
/*
* The following log levels are as follows:
--- 2009-03-27.orig/xen/include/xen/lib.h 2009-03-30 09:11:46.000000000 +0200
+++ 2009-03-27/xen/include/xen/lib.h 2009-04-07 13:43:03.000000000 +0200
@@ -18,6 +18,12 @@ void __warn(char *file, int line);
/* Force a compilation error if condition is true */
#define BUILD_BUG_ON(condition) ((void)sizeof(struct { int:-!!(condition); }))
+/* Force a compilation error if condition is true, but also produce a
+ result (of value 0 and type size_t), so the expression can be used
+ e.g. in a structure initializer (or where-ever else comma expressions
+ aren''t permitted). */
+#define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:-!!(e); }))
+
#ifndef assert_failed
#define assert_failed(p) \
do { \
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On 20/05/2009 06:04, "Jan Beulich" <JBeulich@novell.com> wrote:> Cloning the similar construct from Linux, allowing to detect improper > uses of ARRAY_SIZE() at build time. > > Signed-off-by: Jan Beulich <jbeulich@novell.com>Would simply removing the cast to void from BUILD_BUG_ON() lead to compiler warnings? -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
>>> Keir Fraser <keir.fraser@eu.citrix.com> 20.05.09 15:15 >>> >On 20/05/2009 06:04, "Jan Beulich" <JBeulich@novell.com> wrote: > >> Cloning the similar construct from Linux, allowing to detect improper >> uses of ARRAY_SIZE() at build time. >> >> Signed-off-by: Jan Beulich <jbeulich@novell.com> > >Would simply removing the cast to void from BUILD_BUG_ON() lead to compiler >warnings?While I didn''t try it, I''m convinced it would. Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
On 20/05/2009 06:39, "Jan Beulich" <JBeulich@novell.com> wrote:>> Would simply removing the cast to void from BUILD_BUG_ON() lead to compiler >> warnings? > > While I didn''t try it, I''m convinced it would.I tried it (gcc 4.1.2) and it didn''t. And I''m not sure what the theoretical warning message would be: Throwing away a non-void value? We do that with return values from functions very often. I''ll change BUILD_BUG_ON() and avoid BUILD_BUG_ON_ZERO(), but revert to your approach if some gccs turn out to act differently. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
On 20/05/2009 07:05, "Keir Fraser" <keir.fraser@eu.citrix.com> wrote:>> While I didn''t try it, I''m convinced it would. > > I tried it (gcc 4.1.2) and it didn''t. And I''m not sure what the theoretical > warning message would be: Throwing away a non-void value? We do that with > return values from functions very often. > > I''ll change BUILD_BUG_ON() and avoid BUILD_BUG_ON_ZERO(), but revert to your > approach if some gccs turn out to act differently.Actually I suppose having ZERO in the name is nice in arithmetic expressions. So I''ll just check in as-is after all. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel