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Mail Archives: djgpp/2009/05/04/18:17:52

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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 15:07:21 -0700 (PDT)
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

On May 4, 6:07=A0am, Eli Zaretskii <e DOT  DOT  DOT  AT gnu DOT org> wrote:
> > From: Rugxulo <rugx DOT  DOT  DOT  AT gmail DOT com>
> > Date: Sun, 3 May 2009 17:23:31 -0700 (PDT)
>
> > Lots of inline AT&T in that file. Very confusing although I
> > (unsurprisingly) admit to knowing nothing about the FPU and DPMI
> > exceptions.
>
> This is unrelated to DPMI exceptions. =A0It is simply a matter with what
> instructions to use to save and restore the FPU state when jumping
> between the debugger and the debuggee (since they both run in the same
> process on DOS).
>
> I really don't see any sense in modifying the library unless there's
> going to be a release of v2.04 soon. =A0

Not going to happen. While CWS showed some interest, and obviously
there are people interested in it (me), there's just not enough
manpower for it at the moment. Maybe next year, who knows. DJ must be
really really busy at the moment.

> As Charles points out, adding
> SSE support will need code added to determine whether FXSAVE/FXRSTOR
> are supported before we use them, and a lot of testing to make sure we
> don't break old machines.

1). See if CPUID supported (bit 21 of eflags)
2). See if FXSAVE / FXRSTOR supported (bit 24 of edx result from cpuid
eax=3D1)
3). See if SSE supported (SSE1 is bit 25 of edx result from cpuid
eax=3D1, SSE2 is bit 26, SSE3 is bit 0 of ecx)
4). If not already using CWSDPMI r5 2008, set bit 9 (OSFXSR) of CR4
and turn off bit 2 of CR0 (EM - emulation) -- typically done in ring
0, but some ring 3 environments emulate it for you (JEMM386)

Technically, FXSAVE / FXRSTOR is also supported on late model PIIs
also, which don't have SSE.

> OTOH, if someone needs it badly on a machine that is known to support
> 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.

> > Maybe somebody can find Pierre Muller and bug him to work
> > on it (doubtful).
>
> Pierre is very active on the GDB forum, so he is easy to find. =A0But I
> don't think he wrote the code in question.

No idea, but it mentioned his name, so I figured he at least
understood the file.    :-)

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