Re: building i386 world on amd64 host: failed @svn
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On Fri, Aug 16, 2013 at 02:33:29PM +0200, Dimitry Andric wrote:
> 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 ?=20
> >>>> 64 bit atomics cannot be implemented in usermode on i386 on=20
> >>>> processors which do not have cmpxchg8b instruction.
> >>>=20
> >>> Ah yes, you are totally right, with -v it gives:
> >>>=20
> >>> COLLECT_GCC_OPTIONS=3D'-O2' '-S' '-v' '-mtune=3Dgeneric'
> >>> '-march=3Di586'
> >>>=20
> >>> So we should really disable atomics for i486 and lower? Though I
> >>> have understood that there also some pentiums without
> >>> cmpxchg8b...
> >>=20
> >> 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).
> >=20
> > It is actually little complicated.
> >=20
> > http://www.geoffchappell.com/studies/windows/km/cpu/cx8.htm
>=20
>=20
> In contrast, gcc's rules (in contrib/gcc/config/i386/i386.c) are pretty
> straightforward:
>=20
> /* Compare and exchange was added for 80486. */
> const int x86_cmpxchg =3D ~m_386;
> /* Compare and exchange 8 bytes was added for pentium. */
> const int x86_cmpxchg8b =3D ~(m_386 | m_486);
>=20
> So maybe the following is a safe enough solution for now:
>=20
> Index: usr.bin/svn/svn_private_config.h
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> --- 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
>=20
> /* Define if compiler provides atomic builtins */
> +#if !defined(__i386__) || !defined(__i486__)
> #define SVN_HAS_ATOMIC_BUILTINS 1
> +#endif
I do not understand this. Isn't __i386__ defined always when compiling
for 32bit x86 ? =20
The !defined(__i486__) part assumes that any other cpu variation supported
by compiler has cmpxchg8b.
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