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From: Rugxulo <rugxulo AT gmail DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Please help resurrecting GDB for version 7.0 release
Date: Mon, 4 May 2009 22:28:28 -0700 (PDT)
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To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Reply-To: djgpp AT delorie DOT com

Hi again,

On May 5, 12:08=A0am, Rugxulo <rugx DOT  DOT  DOT  AT gmail DOT com> wrote:
>
> On May 4, 10:10=A0pm, Eli Zaretskii <e DOT  DOT  DOT  AT gnu DOT org> wrote:
>
> In other words, I would've thought you could do the following in ring
> 3, but apparently not:
>
> =A0 mov eax,cr4 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0; (CR4 first introduced in=
 Pentium)
> =A0 bt eax,OSFXSR =A0 =A0 =A0 =A0 =A0 =A0 =A0; if already set, no need to=
 enable
> =A0 jc .bye

And yet I just tested again on Vista (since the above was from
memory), and it seems to work! So either I tested wrong, got confused,
or it's a bug in XP (which I can't test at the moment), most likely
one of the former. Fun fun fun.   :-P

> > All this just to have a change in a version that isn't going
> > to be released any time soon? =A0Doesn't sound like a good investment o=
f
> > my scarce resources.
>
> > > > OTOH, if someone needs it badly on a machine that is known to suppo=
rt
> > > > these instructions, they can simply replace FNSAVE/FRSTOR with the
> > > > extended instructions, modify the definition of the NPX object in
> > > > debug/dbgcom.h to accommodate for the extra registers, and be done.
>
> > > You make it sound trivial, not sure it is.
>
> > It's trivial. =A0You can try it.
>
> FXSAVE / FXRSTOR use a 512-byte buffer, but not all of that is used (I
> think), esp. if SSE is not already enabled (which is how Agner Fog
> claims Intel told him to know whether it is enabled ... see if it
> saves / restores the SSE "xmm0" etc. registers.).
>
> Did any of that help? I hope I explained / understood it correctly!