The patch titled
kernel.h: add BUILD_BUG_ON_NOT_POWER_OF_2()
has been added to the -mm tree. Its filename is
kernelh-add-build_bug_on_not_power_of_2.patch
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See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: kernel.h: add BUILD_BUG_ON_NOT_POWER_OF_2()
From: Roland Dreier <rdreier@xxxxxxxxx>
When code relies on a constant being a power of 2:
#define FOO 512 /* must be a power of 2 */
it would be nice to be able to do:
BUILD_BUG_ON(!is_power_of_2(FOO));
However applying an inline function does not result in a compile-time
constant that can be used with BUILD_BUG_ON(), so trying that gives
results in:
error: bit-field '<anonymous>' width not an integer constant
As suggested by akpm, rather than monkeying around with is_power_of_2()
and risking gcc warts about constant expressions, just create a macro
BUILD_BUG_ON_NOT_POWER_OF_2() to encapsulate this common requirement.
Signed-off-by: Roland Dreier <rolandd@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/kernel.h | 4 ++++
1 file changed, 4 insertions(+)
diff -puN include/linux/kernel.h~kernelh-add-build_bug_on_not_power_of_2 include/linux/kernel.h
--- a/include/linux/kernel.h~kernelh-add-build_bug_on_not_power_of_2
+++ a/include/linux/kernel.h
@@ -703,6 +703,10 @@ static inline void ftrace_dump(void) { }
struct sysinfo;
extern int do_sysinfo(struct sysinfo *info);
+/* Force a compilation error if expression is not a power of 2 */
+#define BUILD_BUG_ON_NOT_POWER_OF_2(n) \
+ BUILD_BUG_ON(((n) != 0 && (((n) & ((n) - 1)) == 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
e.g. in a structure initializer (or where-ever else comma expressions
_
Patches currently in -mm which might be from rdreier@xxxxxxxxx are
kfifo-use-void-pointers-for-user-buffers.patch
kfifo-make-kfifo_in-atomic.patch
kfifo-sanitize-_user-error-handling.patch
kfifo-add-kfifo_out_peek.patch
kfifo-add-kfifo_initialized.patch
kfifo-document-everywhere-that-size-has-to-be-power-of-two.patch
kernelh-add-build_bug_on_not_power_of_2.patch
ecryptfs-another-lockdep-issue.patch
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