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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] Crash due to invalid env->current_tb
Date: Thu, 1 May 2008 17:04:43 +0100
References: <20080429115614.GA15524@os.inf.tu-dresden.de>
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To: qemu-devel@nongnu.org
Cc: Blue Swirl <blauwirbel@gmail.com>

> >                  T0 = gen_func();
> >
> >  For 64bit target T0 is 64bits so "=a" does not work and "=A" is needed.
> >  The strange thing is that I need to throw away the upper 32bits because
> >  otherwise it won't work. gen_func is defined to return just long but T0
> >  is unsigned long long, this seems inconsistent. The 'and' does not
> >  appear in 32bit targets so it does not harm there.
>
> This is because in this special case, T0 is not used as target CPU
> temporary, but instead to return next TB address. On i386 this is 32
> bits, so only EAX is needed. TCG does not touch EDX, so it contains
> garbage. This also means that moving EDX to high word of T0 and then
> throwing the high word away may be slightly wasteful.

Do we need to use T0 at all here? Can't we just use a normal local variable?

Paul