Re: PATCH: Enable x86 XML target descriptions

[Mark Kettenis <mark.kettenis@xs4all.nl>]

> Date: Mon, 22 Feb 2010 12:03:03 -0500
> From: Daniel Jacobowitz <dan@codesourcery.com>
> 
> On Mon, Feb 22, 2010 at 05:56:58PM +0100, Mark Kettenis wrote:
> > I've looked at the Linux kernel sources for the kernel on my
> > workstation (2.6.27 in its OpenSUSE incarnation), and the only way to
> > distinguish between a 32-bit and a 64-bit process seems to be to
> > attempt to write one of the debug address registers with a value
> > that's larger than 0xffffffff.  If that fails, you have a 32-bit
> > process, otherwise it's a 64-bit process.
> 
> Yuck :-(  But I didn't see anything else either.

Indeed.

> Is there an eflags bit for this?  Even if so, IIRC, we may not want to
> use it; it's possible to run 32-bit code in a 64-bit process and some
> overly clever programs may do so.

Nope, there is no %eflags/%rflags bit for this.  Not quite sure what
running 32-bit code in a 64-bit process actually means.  But I'd guess
you want the 64-bit view on the registers in that case.

Anyway, I think it's probably best if HJ leaves this bit out of this
diff for now.  We can revisit the issue when AVX support is
introduced.