Re: [Mingw-users] src/winsup/w32api ChangeLog include/winnt.h

[Earnie B. <ea...@us...>]

On Thu, Aug 2, 2012 at 8:54 AM, Václav Zeman wrote:
> On 2 August 2012 13:12, Earnie Boyd wrote:
>> On Thu, Aug 2, 2012 at 4:40 AM, Václav Zeman wrote:
>>> On 1 August 2012 21:17,  <earnie@...> wrote:
>>>> CVSROOT:        /cvs/src
>>>> Module name:    src
>>>> Changes by:     earnie@...   2012-08-01 19:17:37
>>>>
>>>> Modified files:
>>>>         winsup/w32api  : ChangeLog
>>>>         winsup/w32api/include: winnt.h
>>>>
>>>> Log message:
>>>>         * include/winnt.h (MemoryBarrier): Add definition.
>>>>
>>>> Patches:
>>>> http://sourceware.org/cgi-bin/cvsweb.cgi/src/winsup/w32api/ChangeLog.diff?cvsroot=src&r1=1.1121&r2=1.1122
>>>> http://sourceware.org/cgi-bin/cvsweb.cgi/src/winsup/w32api/include/winnt.h.diff?cvsroot=src&r1=1.139&r2=1.140
>>>>
>>>
>>> +# else
>>> +   FORCEINLINE VOID MemoryBarrier (VOID) {
>>> +       LONG Barrier = 0;
>>> +       __asm__ __volatile__("xchgl %%eax,%0 "
>>> +         :"=r" (Barrier));
>>> +   }
>>>
>>> Since this is for GCC anyway, why not using __sync_synchronize() in
>>> the body of the function instead?
>>
>> I found the code elsewhere and rather trust the author of that bit.
>> However, if you can provide test programs showing the differences of
>> both methods I'll consider a change.
> The differences are 'lock orl   $0, (%esp)' or 'mfence', depending on
> -march= switch, versus your 'xchg' instruction. GCC's versions are not
> using any extra variable and GCC can also use the mfence instruction
> which seems like something favourable and future proof.

As I've said I trust the source of the code to be correct.  If you can
prove a fallacy then I will bring it up with the project from which I
took the code.  Otherwise it is what it is; especially since I'm not
that good with assembler.

-- 
Earnie
-- https://sites.google.com/site/earnieboyd