Re: [Qemu-devel] [PULL 00/23] TCG and misc patches for 2.7 hard freeze from 2016-07-18

[Peter Maydell]

On 18 July 2016 at 14:22, Paolo Bonzini <address@hidden> wrote:
>
>
> On 18/07/2016 14:50, Peter Maydell wrote:
>> On 18 July 2016 at 12:59, Paolo Bonzini <address@hidden> wrote:
>>>
>>>
>>> On 18/07/2016 13:57, Peter Maydell wrote:
>>>> On 18 July 2016 at 12:54, Paolo Bonzini <address@hidden> wrote:
>>>>> On 18/07/2016 13:51, Peter Maydell wrote:
>>>>>> Looks like an attempt to do an atomic op on a larger-than-host-pointer 
>>>>>> type.
>>>>>
>>>>> Hmm, atomic_set should be acceptable even on 64-bit.
>>>>
>>>> How does that work, when the host might not have an atomic
>>>> 64-bit write?
>>>
>>> All hosts we support should have it.
>>
>> 32-bit ARM does not guarantee that you can have 64-bit atomic
>> operations.
>
> Doesn't it have LDRDEX and STRDEX?

Yes, you could use a LDREXD/STREXD sequence for ARMv7 (and it
looks like gcc does so). Doesn't work on ARMv5, though.

MIPS32 and PPC32 are the hosts where attempted 64-bit
atomics generally fail (they want to call out to libatomic),
so those would be the other ones to test before widening the use
of atomic_set.

thanks
-- PMM