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Re: Disable 64-bit atomics for MIPS n32 [committed]


On Wed, 2015-01-28 at 14:04 -0800, H.J. Lu wrote:
> On Wed, Jan 28, 2015 at 1:48 PM, Chris Metcalf <cmetcalf@ezchip.com> wrote:
> > On 1/28/2015 4:31 PM, Torvald Riegel wrote:
> >>
> >> On Wed, 2015-01-28 at 18:45 +0000, Joseph Myers wrote:
> >>>
> >>> This patch disables use of 64-bit atomics for MIPS n32 to fix the
> >>> problems with unaligned semaphores.
> >>
> >> That works.  I would probably preferred to just do this in the semaphore
> >> bits (ie, checking for __HAVE_64B_ATOMICS and _LP64, but both have the
> >> same effect for 2.21.
> >
> >
> > You would then have disabled 64-bit atomics for x32, which may not
> > be the solution preferred by H.J.
> >
> 
> I am OK to disable 64-bit atomics in semaphore for x32 in 2.21. We can
> look for a better solution in 2.22.  But the name, __HAVE_64B_ATOMICS,
> is very much misleading.  How about
> 
> __HAVE_64B_ATOMICS_FOR_SEMAPHORE

We could have that *additionally*, but the intent behind
__HAVE_64B_ATOMCIS was to allow archs to express whether they have
HW-supported 64b atomic operations at all, and in such a way that makes
sense for general use (e.g., not just cmpxchg8b or what it's called on
i686).


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