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Re: [Qemu-devel] softmmu_header: ldb_kernel vs. ldsb_kernel


From: Clemens Kolbitsch
Subject: Re: [Qemu-devel] softmmu_header: ldb_kernel vs. ldsb_kernel
Date: Tue, 2 Oct 2007 19:06:10 +0200
User-agent: KMail/1.9.6

> > The only difference I see (that really matters) is how the bytes are
> > copied to the result-pointer (i.e. using movzbl vs. movsbl)... but that's
> > it.
>
> It is a cast. The generic C version for the other architectures makes
> this more obvious.
>
> > If there is some deeper reason behind that - could you please point that
> > out to me? And if there is such a thing, why is it not necessary for
> > storing (e.g. stb_kernel)??
>
> A load (sign-)extends a value to register size, a store doesn't.
>
> That's why you have e.g. in the MIPS instruction set LB, LBU and SB
> but no SBU, it would do the same as SB.

all right .. thanks for the fast answer :-)




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