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Re: [Lightning] How to call varargs functions from lightning in x86_64?

From: Paulo César Pereira de Andrade
Subject: Re: [Lightning] How to call varargs functions from lightning in x86_64?
Date: Mon, 16 Aug 2010 17:50:25 -0300
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Paolo Bonzini wrote:
>>  I am wondering about the rex.WB prefix, is that correct?
> Unless you show the failure happens in the call instruction, yes.  The

  That just shows that I was looking at the wrong possible cause of the
problem at first :-)

> problem is that arguments to variadic functions are passed on the
> stack, not in registers.  That's by the way also why prototypes are
> necessary for variadic functions.
> It's not insurmountable, but it needs a new form of prepare statement
> or something like that.

  This is something that can be worked around most times, but I
believe would be good to have proper support directly in lightning,
for completeness.

  The testing tool is probably some kind of special case, where
proper support for calling varargs is very, very desirable.

  In the case of my use of lightning in my vm, it did only call one
vararg function, that would always receive none or a single string
argument, so, that was easy to workaround...

> Paolo


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