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Re: [Qemu-arm] [Qemu-devel] [RFC v1 3/3] target/arm: Correct exclusive s
From: |
Richard Henderson |
Subject: |
Re: [Qemu-arm] [Qemu-devel] [RFC v1 3/3] target/arm: Correct exclusive store return value |
Date: |
Fri, 11 Aug 2017 13:38:06 -0700 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 |
On 08/11/2017 01:29 PM, Alistair Francis wrote:
> On Fri, Aug 11, 2017 at 1:24 PM, Richard Henderson
> <address@hidden> wrote:
>> On 08/11/2017 01:13 PM, Alistair Francis wrote:
>>>>> + tcg_gen_ext_i64(val, val, memop);
>>>>
>>>> What is this addition intended to accomplish? Because of the position
>>>> within
>>>> the code, you know that memop contains MO_64, so that this is a no-op.
>>>
>>> This is when size == 2 so it's a 32bit operation so memop contains MO_32.
>>
>> It's a paired 32-bit operation, so we're operating on a 64-bit quantity. So
>> extending from 32-bits would be actively wrong.
>
> From what I can see though, the 32bit memop is carried into the
> tcg_gen_atomic_cmpxchg_i64() call so the value returned to tmp is
> masked by the 32bit operation.
>
> Is passing down MO_32 into tcg_gen_atomic_cmpxchg_i64() wrong then as
> it ends up as a 64-bit operation?
If we're passing MO_32 down to cmpxchg_i64 for this case, you have indeed found
a bug. I'll investigate this further on Monday.
r~
- [Qemu-arm] [RFC v1 0/3] Fixup exclusive store logic, Alistair Francis, 2017/08/11
- [Qemu-arm] [RFC v1 1/3] target/arm: Update the memops for exclusive load, Alistair Francis, 2017/08/11
- [Qemu-arm] [RFC v1 2/3] tcg/tcg-op: Expose the tcg_gen_ext_i* functions, Alistair Francis, 2017/08/11
- [Qemu-arm] [RFC v1 3/3] target/arm: Correct exclusive store return value, Alistair Francis, 2017/08/11
- Re: [Qemu-arm] [Qemu-devel] [RFC v1 3/3] target/arm: Correct exclusive store return value, Richard Henderson, 2017/08/11
- Re: [Qemu-arm] [Qemu-devel] [RFC v1 3/3] target/arm: Correct exclusive store return value, Alistair Francis, 2017/08/11
- Re: [Qemu-arm] [Qemu-devel] [RFC v1 3/3] target/arm: Correct exclusive store return value, Richard Henderson, 2017/08/11
- Re: [Qemu-arm] [Qemu-devel] [RFC v1 3/3] target/arm: Correct exclusive store return value, Alistair Francis, 2017/08/11
- Re: [Qemu-arm] [Qemu-devel] [RFC v1 3/3] target/arm: Correct exclusive store return value,
Richard Henderson <=
- Re: [Qemu-arm] [Qemu-devel] [RFC v1 3/3] target/arm: Correct exclusive store return value, Alistair Francis, 2017/08/11
- Re: [Qemu-arm] [Qemu-devel] [RFC v1 3/3] target/arm: Correct exclusive store return value, Alistair Francis, 2017/08/11