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Date: Thu, 2 Aug 2007 22:06:16 -0300
From: "Daniel da Veiga" <danieldaveiga@gmail.com>
To: gentoo-user@lists.gentoo.org
Subject: Re: [gentoo-user] Re: Cannot compile texinfo: Illegal instruction -> Wrong -march and -mtune flags?
In-Reply-To: <200708030007.53311.f.philipp@addcom.de>
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On 8/2/07, Florian Philipp <f.philipp@addcom.de> wrote:
> Am Donnerstag 02 August 2007 23:36 schrieb Alexander Skwar:
> > =B7 Florian Philipp <f.philipp@addcom.de>:
> > > You see, they are not compatible and even if some code works I wouldn=
't
> > > bet multimedia apps will perform well.
> > >
> > > With -mtune the instruction set stays the same. It is just "rearrange=
d".
> >
> > Hm. Allright. When using just -mtune (ie. without -march), the
> > docs at
> > http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/i386-and-x86_002d64-Options=
.htm
> >l
> >
> > say:
> > | While picking a specific cpu-type will schedule things appropriately
> > | for that particular chip, the compiler will not generate any code tha=
t
> > | does not run on the i386 without the -march=3Dcpu-type option being u=
sed.
> >
> > If -mtune=3Dathlon-xp is used, code is generated which may make
> > use of 3dNOW!. 3dNOW! is, of course, not to be found on 386 :)
> > If the instruction set stays the same, code generated with
> > -mtune=3Dathlon-xp would not be executable on 386 machines, if
> > I understand you correctly.
> >
> > Hm. With -mtune, the set of available instructions (ie.
> > stuff like 3dNOW!, I suppose?) is NOT changed from the default
> > of i386, is it? Or what does "Tune to cpu-type everything applicable
> > about the generated code, except for the ABI and the set of available
> > instructions." mean - especially note the "except for [...] the set of
> > available instructions" part.
> >
> > So with "-mtune=3Dpentium-m -march=3Dathlon-xp" I'm making the compiler
> > generate code which is "ordered" the way it's best for pentium-m
> > machines while allowing it to use athlon-xp instruction set? Is
> > that what I'm doing?
> >
> > If so, then it seems you're right - code will run, but maybe not
> > so well.
> >
> > Is that understanding correct? If so, then I really should think
> > twice about using "-mtune=3Dpentium-m -march=3Dathlon-xp", shouldn't
> > I?
> >
> > Curious,
> >
> > Alexander Skwar
> > --
>
> At least that's how I understand the issue. At the moment I've got two id=
eas
> to solve your problem:
>
> 1. set march to an inferior target (pentium-3 and pentium-3m seem okay: m=
mx
> and sse) and mtune for one (or even both?) of them
> 2. set march to one of them and disable incompatible instruction sets wit=
h
> options like -mno-sse2 or -mno-3dnow
>
>
Isn't the -march=3Di686 valid?
I guess that would be the most "compatible" option for binaries that
will run on AMD and Intel processors... Or simply use no "-march"
setting, only "-mtune"... I did that recently to switch a whole system
from an Athlon XP to a Intel Core Duo...
--=20
Daniel da Veiga
Computer Operator - RS - Brazil
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