On Thu, Sep 04, 2014 at 08:42:44AM -0700, Jarno Rajahalme wrote:
> Small nits below, otherwise looks good to me (even though I?m not versed in
> MSVC),
>
> Signed-off-by: Jarno Rajahalme <jrajaha...@nicira.com>
>
> On Sep 3, 2014, at 1:08 PM, Gurucharan Shetty <shet...@nicira.com> wrote:
> >
> > +/* 64 bit writes are atomic on i586 if 64 bit aligned. */
> > +#define atomic_store64(DST, SRC, ORDER)
> > \
> > + if (((size_t) (DST) & (sizeof *(DST) - 1)) == 0) {
> > \
> > + if (ORDER == memory_order_seq_cst) {
> > \
> > + InterlockedExchange64((int64_t volatile *) (DST),
> > \
> > + (int64_t) (SRC));
> > \
> > + } else {
> > \
> > + *(DST) = (SRC);
> > \
> > + }
> > \
> > + } else {
> > \
> > + abort();
> > \
> > + }
> > +
>
> How about this instead:
>
> /* 64 bit writes are atomic on i586 if 64 bit aligned. */
> #define atomic_store64(DST, SRC, ORDER) \
> if (((size_t) (DST) & (sizeof *(DST) - 1)) \
> || ORDER == memory_order_seq_cst) { \
> InterlockedExchange64((int64_t volatile *) (DST), \
> (int64_t) (SRC)); \
> } else { \
> *(DST) = (SRC); \
> } \
>
> However, you should probably keep the version in your patch if you
> know that the alignment check can be computed at compile-time and/or
> there is some documentation that MSVC will not align 64-bit units on
> at 4-byte alignment.
http://msdn.microsoft.com/en-us/library/ee959491.aspx says that MSVC
cannot align 64-bit types on 64-bit boundaries, at least on the stack:
Data types that are larger than 4 bytes are not automatically
aligned on the stack when you use the x86 compiler to compile an
application. Because the architecture for the x86 compiler is a 4
byte aligned stack, anything larger than 4 bytes, for example, a
64-bit integer, cannot be automatically aligned to an 8-byte
address.
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