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Mail Archives: djgpp/2009/05/05/01:45:51

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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 22:33:20 -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 yet again,


On May 5, 12:28=A0am, Rugxulo <rugx DOT  DOT  DOT  AT gmail DOT com> wrote:
>
> 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. =A0 :-P

And by "seems to work", I mean it doesn't cause an exception. Stepping
through with GDB (and yes, I used "volatile" just in case) shows that
EAX is 0 after the move, so that's not helpful at all. Must be
virtualized in ring 3 like eflags is, in other words not reliable at
all.

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