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FromNikita Danilov <>
DateSun, 23 Oct 2005 20:54:35 +0400
SubjectRe: [PATCH 7/9] mm: split page table lock
Digg This
Hugh Dickins writes:

[...]

+ * When freeing, reset page->mapping so free_pages_check won't complain. + */
+#define __pte_lockptr(page) ((spinlock_t *)&((page)->private)) +#define pte_lock_init(_page) do { \
+ BUILD_BUG_ON((size_t)(__pte_lockptr((struct page *)0) + 1) > \ + sizeof(struct page)); \
+ spin_lock_init(__pte_lockptr(_page)); \
+} while (0)

Looking at this, I think BUILD_BUG_ON() should be defined in a way that allows it to be used outside of function scope too (see patch below, compile-tested).

Nikita.
--
Fix comment describing BUILD_BUG_ON: BUG_ON is not an assertion (unfortunately).

Also implement BUILD_BUG_ON in a way that can be used outside of a function scope, so that compile time checks can be placed in convenient places (like in a header, close to the definition of related constants and data-types).
Signed-off-by: Nikita Danilov <nikita@clusterfs.com>
 include/linux/kernel.h |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

[view this diff only]
diff -puN include/linux/kernel.h~BUILD_BUG_ON-fix-comment include/linux/kernel.h
--- git-linux/include/linux/kernel.h~BUILD_BUG_ON-fix-comment	2005-10-23 20:09:33.000000000 +0400
+++ git-linux-nikita/include/linux/kernel.h	2005-10-23 20:44:03.000000000 +0400
@@ -307,8 +307,9 @@ struct sysinfo {
 	char _f[20-2*sizeof(long)-sizeof(int)];	/* Padding: libc5 uses this.. */
 };
 
-/* Force a compilation error if condition is false */
-#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
+/* Force a compilation error if condition is true */
+#define BUILD_BUG_ON(x)							\
+	void __dummy_build_bug_on(int __compile_time_assertion_failed_[-!!(x)])
 
 #ifdef CONFIG_SYSCTL
 extern int randomize_va_space;
_
\
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