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Date: Sun, 26 May 2013 10:33:35 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] i386/translate: ignore 0x67 (PREFIX_ADR)
 on TARGET_X86_64 && CODE64()
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To: Richard Henderson <rth@twiddle.net>
Cc: Laszlo Ersek <lersek@redhat.com>, qemu-devel@nongnu.org

Il 26/05/2013 01:23, Richard Henderson ha scritto:
> On 2013-05-24 14:37, Laszlo Ersek wrote:
>> @@ -4813,7 +4813,11 @@ static target_ulong disas_insn(CPUX86State
>> *env, DisasContext *s,
>>               /* 0x66 is ignored if rex.w is set */
>>               dflag = 2;
>>           }
>> -        if (!(prefixes & PREFIX_ADR)) {
>> +        if (prefixes & PREFIX_ADR) {
>> +            /* flip it back, 0x67 should have no effect */
>> +            aflag ^= 1;
>> +        }
>> +        else {
>>               aflag = 2;
>>           }
>>       }
>>
> 
> Agreed that there's a bug here.  I'm thinking it would be clearer to not
> write this as yet another flip, but understand that unlike dflag, aflag
> can only be either 1 or 2 in 64-bit mode.
> 
> I'm thinking of something more like this:
> 
> diff --git a/target-i386/translate.c b/target-i386/translate.c
> index 0aeccdb..bf772aa 100644
> --- a/target-i386/translate.c
> +++ b/target-i386/translate.c
> @@ -4813,9 +4813,8 @@ static target_ulong disas_insn(CPUX86State *env,
> DisasContext *s,
>              /* 0x66 is ignored if rex.w is set */
>              dflag = 2;
>          }
> -        if (!(prefixes & PREFIX_ADR)) {
> -            aflag = 2;
> -        }
> +        /* 0x67 toggles between 64-bit and 32-bit addressing.  */
> +        aflag = (prefixes & PREFIX_ADR ? 1 : 2);

Isn't that just "aflag++"?  Needs a comment of course ("toggle between
32- and 64-bit, not 16- and 32-bit.").

Paolo