Messages in this thread |  | | | Date | Mon, 01 Sep 2008 14:55:17 +0100 | | From | "Jan Beulich" <> | | Subject | Re: [PATCH 5/5] debug: BUILD_BUG_ON: error on non-const expressions |
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>>> Boaz Harrosh <bharrosh@panasas.com> 01.09.08 15:28 >>> >--- a/include/linux/compiler.h >+++ b/include/linux/compiler.h >@@ -195,7 +195,10 @@ extern void __chk_io_ptr(const volatile void __iomem *); > #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x)) > > /* Force a compilation error if condition is true */ >-#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)])) >+#define BUILD_BUG_ON(condition) \ >+do { \ >+ static struct { char arr[1 - 2*!!(condition)]; } x __maybe_unused;\ >+} while(0) > > /* 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
I have to admit that I'm surprise this compiles: You replace an expression with a statement, and hence you reduce the places where BUILD_BUG_ON() can validly be used. Of course you could wrap the whole thing in ({}), but I can't see why not to use a bit-field to achieve the intended effect. Also, are you sure the compiler will eliminate the dead variable in all cases?
Finally, using as common a variable as 'x' here seems dangerous, too: What if somewhere x is #define-d to something more complex than a simple identifier?
Jan
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