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From: Peter Maydell <peter.maydell@linaro.org>
Date: Fri, 20 Dec 2013 16:29:22 +0000
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Subject: Re: [Qemu-devel] [PATCH 02/21] target-arm: A64: add support for
	ld/st unsigned imm
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To: Richard Henderson <rth@twiddle.net>
Cc: Patch Tracking <patches@linaro.org>, Michael Matz <matz@suse.de>, QEMU Developers <qemu-devel@nongnu.org>, Claudio Fontana <claudio.fontana@linaro.org>, Dirk Mueller <dmueller@suse.de>, Will Newton <will.newton@linaro.org>, Laurent Desnogues <laurent.desnogues@gmail.com>, =?UTF-8?B?QWxleCBCZW5uw6ll?= <alex.bennee@linaro.org>, "kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>, Christoffer Dall <christoffer.dall@linaro.org>

On 20 December 2013 16:26, Richard Henderson <rth@twiddle.net> wrote:
> On 12/20/2013 08:08 AM, Peter Maydell wrote:
>>> In particular, opc = 2 && size = 2 should be unallocated.
>>
>> This is LDRSW (immediate), not unallocated, isn't it?
>>
>> I agree the decode logic isn't laid out the same as the ARM ARM,
>> but I'm pretty sure it's correct.
>
> Oops, typo: opc=3 && size=2.  Basically,
>
>
>   if opc<1> == '0' then
>     // store or zero-extending load
>     memop = if opc<0> == '1' then MemOp_LOAD else MemOp_STORE;
>     regsize = if size == '11' then 64 else 32;
>     signed = FALSE;
>   else
>     if size == '11' then
>         memop = MemOp_PREFETCH;
>         if opc<0> == '1' then UnallocatedEncoding();
>     else
>         // sign-extending load
>         memop = MemOp_LOAD;
>         if size == '10' && opc<0> == '1' then UnallocatedEncoding();
>
> this one  ----^

+        if (size == 3 && opc == 2) {
+            /* PRFM - prefetch */
+            return;
+        }
+        if (opc == 3 && size > 1) {
+            unallocated_encoding(s);
+            return;
+        }
+        is_store = (opc == 0);
+        is_signed = opc & (1<<1);
+        is_extended = (size < 3) && (opc & 1);

That is caught by 'if (opc == 3 && size > 1)'.

thanks
-- PMM