Date: Fri, 16 Aug 2013 14:33:29 +0200 From: Dimitry Andric <dim@FreeBSD.org> To: Jung-uk Kim <jkim@FreeBSD.org> Cc: Konstantin Belousov <kostikbel@gmail.com>, freebsd-current@FreeBSD.org, Dmitry Morozovsky <marck@rinet.ru>, Peter Wemm <peter@wemm.org> Subject: Re: building i386 world on amd64 host: failed @svn Message-ID: <70C1942B-8BA3-47D8-BFE4-3DC3B5CAD56C@FreeBSD.org> In-Reply-To: <520D2E40.2090704@FreeBSD.org> References: <alpine.BSF.2.00.1307281713160.55051@woozle.rinet.ru> <17A40261-A0DA-4070-990F-0D0777A5BE44@FreeBSD.org> <20130815183640.GR4972@kib.kiev.ua> <D559C583-B0A9-4731-B454-3521635AEC79@FreeBSD.org> <20130815193049.GU4972@kib.kiev.ua> <520D2E40.2090704@FreeBSD.org>
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On Aug 15, 2013, at 21:38, Jung-uk Kim <jkim@FreeBSD.org> wrote: > 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 In contrast, gcc's rules (in contrib/gcc/config/i386/i386.c) are pretty straightforward: /* Compare and exchange was added for 80486. */ const int x86_cmpxchg = ~m_386; /* Compare and exchange 8 bytes was added for pentium. */ const int x86_cmpxchg8b = ~(m_386 | m_486); So maybe the following is a safe enough solution for now: Index: usr.bin/svn/svn_private_config.h =================================================================== --- usr.bin/svn/svn_private_config.h (revision 254300) +++ usr.bin/svn/svn_private_config.h (working copy) @@ -153,7 +153,9 @@ #define SVN_FS_WANT_DB_PATCH 14 /* Define if compiler provides atomic builtins */ +#if !defined(__i386__) || !defined(__i486__) #define SVN_HAS_ATOMIC_BUILTINS 1 +#endif /* Is GNOME Keyring support enabled? */ /* #undef SVN_HAVE_GNOME_KEYRING */ Those rules can be extended for other arches or CPUs that don't support 64-bit atomic operations. -Dimitry
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