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Re: [Lightning] Code patching, context switching

From: Sandro Magi
Subject: Re: [Lightning] Code patching, context switching
Date: Wed, 20 Feb 2008 12:10:13 -0500

On Wed, Feb 20, 2008 at 11:55 AM, Paolo Bonzini <address@hidden> wrote:
>  > I don't get it. Are you saying that the PPC's entire register file is
>  > not accessible via JIT_R, JIT_V and JIT_FPR?
>  Yes.  r3-r9, which the ABI uses for argument passing, are not accessible
>  at all.  In the prolog, they are moved to other, callee-save registers,
>  which are also not accessible with JIT_{R,V} but only with jit_getarg.

That's unfortunate. Is there a good reason for this artificial
limitation? Seems Lightning would be much more flexible as a code
generator with a low-level interface, which is what I assumed
JIT_R/V/FPR were, and a higher-level interface, which is what
jit_getarg and jit_prolog are. I can understand wanting to insulate
the users from inadvertently clobbering the argument registers, but a
low-level api would still be nice.

Anyway, jit_prolog and friends are fine for now, I'm just trying to
plan out my development strategy, so I'll look into this further at
some future point.


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