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Date: Sun, 7 Feb 2010 14:02:31 +0100
Message-ID: <761ea48b1002070502yaf00e06x9630b3fea7e5c106@mail.gmail.com>
Subject: Re: [Qemu-devel] [PATCH 4/4] target-arm: neon fix
From: Laurent Desnogues <laurent.desnogues@gmail.com>
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To: Riku Voipio <riku.voipio@iki.fi>
Cc: qemu-devel@nongnu.org

On Sun, Feb 7, 2010 at 1:54 PM, Laurent Desnogues
<laurent.desnogues@gmail.com> wrote:
> On Fri, Feb 5, 2010 at 4:52 PM, Riku Voipio <riku.voipio@iki.fi> wrote:
>> From: Juha Riihim=E4ki <juha.riihimaki@nokia.com>
>>
>> add an extra check in "two registers and a shift" to ensure element
>> size decoding logic cannot fail.
>>
>> Signed-off-by: Juha Riihim=E4ki <juha.riihimaki@nokia.com>
>> Signed-off-by: Riku Voipio <riku.voipio@nokia.com>
>> ---
>> =A0target-arm/translate.c | =A0 =A03 ++-
>> =A01 files changed, 2 insertions(+), 1 deletions(-)
>>
>> diff --git a/target-arm/translate.c b/target-arm/translate.c
>> index 743b846..8bba034 100644
>> --- a/target-arm/translate.c
>> +++ b/target-arm/translate.c
>> @@ -4567,8 +4567,9 @@ static int disas_neon_data_insn(CPUState * env, Di=
sasContext *s, uint32_t insn)
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 size =3D 3;
>> =A0 =A0 =A0 =A0 =A0 =A0 } else {
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 size =3D 2;
>> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0while (size && (insn & (1 << (size + 19=
))) =3D=3D 0)
>> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0while (size && (insn & (1 << (size + 19=
))) =3D=3D 0) {
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 size--;
>> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0}
>> =A0 =A0 =A0 =A0 =A0 =A0 }
>> =A0 =A0 =A0 =A0 =A0 =A0 shift =3D (insn >> 16) & ((1 << (3 + size)) - 1)=
;
>> =A0 =A0 =A0 =A0 =A0 =A0 /* To avoid excessive dumplication of ops we imp=
lement shift
>
> I think there's a patch ordering problem that makes
> the comment and the change not agree :-)

BTW I don't think adding the check for size is needed
here.  The encoding at that point looks like this:

 3322222222221111111111
 10987654321098765432109876543210
 1111001_1___1______________1____
 1111001_1__1_______________1____
 1111001_1_1________________1____

so it will stop for size =3D=3D 0 given that bit 19 will have to
be set.


Laurent