From e519a84b4370616f997aeef96ecb7d53ac5a3946 Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Thu, 5 Nov 2015 18:45:02 -0800 Subject: compiler.h: add support for function attribute assume_aligned gcc 4.9 added the function attribute assume_aligned, indicating to the caller that the returned pointer may be assumed to have a certain minimal alignment. This is useful if, for example, the return value is passed to memset(). Add a shorthand macro for that. Signed-off-by: Rasmus Villemoes Cc: Christoph Lameter Cc: David Rientjes Cc: Pekka Enberg Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Pranav Vashi --- include/linux/compiler-gcc.h | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) (limited to 'include/linux/compiler-gcc.h') diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index e355d4af4..5216c1ae3 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -188,6 +188,23 @@ #define __visible __attribute__((externally_visible)) #endif + +#if GCC_VERSION >= 40900 +/* + * __assume_aligned(n, k): Tell the optimizer that the returned + * pointer can be assumed to be k modulo n. The second argument is + * optional (default 0), so we use a variadic macro to make the + * shorthand. + * + * Beware: Do not apply this to functions which may return + * ERR_PTRs. Also, it is probably unwise to apply it to functions + * returning extra information in the low bits (but in that case the + * compiler should see some alignment anyway, when the return value is + * massaged by 'flags = ptr & 3; ptr &= ~3;'). + */ +#define __assume_aligned(a, ...) __attribute__((__assume_aligned__(a, ## __VA_ARGS__))) +#endif + /* * GCC 'asm goto' miscompiles certain code sequences: * -- cgit v1.2.3