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Date: Thu, 15 Aug 2013 15:38:40 -0400
From: Jung-uk Kim <jkim@FreeBSD.org>
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To: Konstantin Belousov <kostikbel@gmail.com>
Subject: Re: building i386 world on amd64 host: failed @svn
References: <alpine.BSF.2.00.1307281713160.55051@woozle.rinet.ru>
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Cc: freebsd-current@FreeBSD.org, Dimitry Andric <dim@FreeBSD.org>,
 Dmitry Morozovsky <marck@rinet.ru>, Peter Wemm <peter@wemm.org>
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On 2013-08-15 15:30:49 -0400, Konstantin Belousov wrote:
> On Thu, Aug 15, 2013 at 09:12:52PM +0200, Dimitry Andric wrote:
>> On Aug 15, 2013, at 20:36, Konstantin Belousov
>> <kostikbel@gmail.com> wrote:
>>> Does the linux box defaults to pentium or higher for -march ? 
>>> 64 bit atomics cannot be implemented in usermode on i386 on 
>>> processors which do not have cmpxchg8b instruction.
>> 
>> Ah yes, you are totally right, with -v it gives:
>> 
>> COLLECT_GCC_OPTIONS='-O2' '-S' '-v' '-mtune=generic'
>> '-march=i586'
>> 
>> So we should really disable atomics for i486 and lower?  Though I
>> have understood that there also some pentiums without
>> cmpxchg8b...
> 
> I do not think that there was any Pentium-branded CPU which did
> not implemented cmpxchg8b.  Some late 486 did provided cpuid, but I
> am almost certain that they did not have cmpxchg8b (cannot check
> anyway).

It is actually little complicated.

http://www.geoffchappell.com/studies/windows/km/cpu/cx8.htm

Jung-uk Kim
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