On 01/14/2014 06:03 AM, Peter Zijlstra wrote:
On Tue, Jan 14, 2014 at 10:28:23AM +0800, Daniel J Blueman wrote:
Peter,
I found out that the build failure was caused by the fact that the
__native_word() macro (used internally by compiletime_assert_atomic())
allows only a size of 4 or 8 for x86-64. The data type that I used is a
byte. Is there a reason why byte and short are not considered native?
It seems likely it was implemented like that since there was no existing
need; long can be relied on as the largest native type, so this should
suffice and works here:
There's Alphas that cannot actually atomically adres a byte; I do not
konw if Linux cares about them, but if it does, we cannot in fact rely
on this in generic primitives like this.
Thank for the explanation.
Can we allow architectural override of __native_word() macro? Like
#ifdef __arch_native_word
#define __native_word(t) __arch_native_word(t)
#else
#define __native_word(t) (sizeof(t) == sizeof(int) || sizeof(t) ==
sizeof(long))
#endif
In this way, we can allow x86 to support byte-based atomic type while
restricting the generic macro to int and long only. I will also modify
the code to use cmpxchg() when byte is not an atomic type.
-Longman
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