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Re: [Qemu-devel] [PATCH 2/2] tcg/i386: Reserve register for guest_base i

From: Aurelien Jarno
Subject: Re: [Qemu-devel] [PATCH 2/2] tcg/i386: Reserve register for guest_base if a segment isn't available
Date: Fri, 17 Jul 2015 17:56:26 +0200
User-agent: Mutt/1.5.23 (2014-03-12)

On 2015-07-17 17:30, Paolo Bonzini wrote:
> On 17/07/2015 03:33, Peter Maydell wrote:
> > On 16 July 2015 at 22:25, Richard Henderson <address@hidden> wrote:
> > > This saves 2 insns and 10 bytes from the implementation of
> > > each memory operation.
> > 
> > Do we have an idea of which platforms/configs don't let
> > us have a segment register for guest_base?
> Everything non-Linux I think, which for user-mode emulation means bsd-user.

Linux might also not allow to use a segment register if the prctl call
with ARCH_SET_GS fails. OTOH I have no idea why it can fail, but we
actually check that it doesn't fail before using %gs.

Aurelien Jarno                          GPG: 4096R/1DDD8C9B
address@hidden                 http://www.aurel32.net

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