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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [PATCH] TCG S/390 backend
Date: Tue, 12 May 2009 13:29:42 +0100
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To: qemu-devel@nongnu.org

> I found the problem: TCG does not zero- or sign-extend arguments to
> function calls. Unlike, for instance, AMD64, 32-bit arithmetic ops on
> S/390 leave the upper 32 bits of the destination register untouched, so
> there could be any kind of garbage there. If a helper taking a 64-bit
> argument is called with the result of such an operation, stuff breaks.

You mean an helper that takes a 32-bit value, which happens to be passed in a 
64-bit register? This is a tricky one because as you say, TCG has no concept 
of signed or unsigned values.

I guess we could add some flag bits to the function call for this. 
def-helper.h/tcg_gen_callN already has something similar for identifying 
64-bit arguments.

Paul