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Re: [Qemu-devel] [RISU RFC PATCH v2 04/14] risugen_x86: add module

From: Jan Bobek
Subject: Re: [Qemu-devel] [RISU RFC PATCH v2 04/14] risugen_x86: add module
Date: Thu, 11 Jul 2019 09:10:54 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1

On 7/11/19 5:26 AM, Richard Henderson wrote:
> On 7/10/19 8:21 PM, Jan Bobek wrote:
>> Doesn't B8 (without REX.W) work for x86_64, too? It zeroes the upper
>> part of the destination, so it's effectively zero-extending, and it's
>> one byte shorter than C7 (no ModR/M byte needed).
> Sorry, I shouldn't have been quite so terse.  What I meant is
>   if (!$is_x86_64 || (0 <= $imm && $imm <= 0xffffffff))
> so that 32-bit always uses the 5-byte encoding instead of the 6-byte.

Oh, I see. I double-checked my new code and it never uses the C7 move
in 32-bit mode, but thanks for pointing it out.


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