Re: [Qemu-devel] Drop support for 32bit hosts in qemu? (was: [PULL 1/6] audio/hda: create millisecond timers that handle IO)

[Laurent Vivier]

Le 27/06/2018 à 20:44, Dr. David Alan Gilbert a écrit :
> * Laurent Vivier (address@hidden) wrote:
>> Le 27/06/2018 à 15:33, Philippe Mathieu-Daudé a écrit :
>>> On 06/27/2018 06:09 AM, Thomas Huth wrote:
>>>> On 27.06.2018 10:52, Gerd Hoffmann wrote:
>>>>>   Hi,
>>>>>
>>>>>>> Is QEMU still useful on 32-bit hosts?  Honest question!
>>>>>>
>>>>>> I guess it depends on what 32-bit hosts you consider. If you look at only
>>>>>> x86 vs. x86_64 then probably x86 is not that important any more but for 
>>>>>> some
>>>>>> embedded systems/SoCs 32bit might still be common and QEMU useful for 
>>>>>> those
>>>>>> (also as host not only emulated).
>>>>>
>>>>> Well.  I've used kvm with an 32bit arm soc (cubietruck).  It's very
>>>>> slow.  And all the arm architecture improvements to support kvm better
>>>>> are for aarch64 only.
>>>>>
>>>>>> Another option might be to not support audio/hda on 32bit hosts. It's not
>>>>>> nice either but a lot nicer than dropping support for 32bit hosts
>>>>>> alltogether to fix a problem in device emulation.
>>>>>
>>>>> But it also is not useful and a waste of resources to maintain 32bit
>>>>> host compatibility if nobody actually uses that ...
>>>>>
>>>>> For me testbuilds are the only reason to compile qemu for 32bit hosts.
>>>>> Since years.
>>>>
>>>> Well, while that's true for you, me and likely most of us developers,
>>>> you can not know whether this is also true for all users of qemu. Thus
>>>> this needs to be announced first for a couple of releases so that people
>>>> have a chance to speak up whether they still need this or not. As
>>>> mentioned earlier, embedded devices are often still 32-bit and I know
>>>> that there really are people who use QEMU on embedded devices.
>>>>
>>>> But I think we could at least announce now already that we intend to
>>>> drop support for 32-bit hosts in the future (maybe not in 2 releases
>>>> already, but, let's say in 2020? 2020 is already the EOL of Python 2, so
>>>> that will rule out a bunch of other legacy hosts, too).
>>>
>>> linux-user is certainly widely used on ARMv6 / ARMv7.
>>>
>>> Known user cases:
>>>
>>> - run ARMv7 binaries on ARMv6
>>> - run armhf binaries on armel
>>> - run x86-64 binaries on ARMv7
>>>
>>
>> I run i386 binaries on ARMv6.
> 
> Do you know if that model has the 64bit atomics (ldrexd/strexd)?

http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0489e/Cihbghef.html

"ARM LDREXB, LDREXH, LDREXD, STREXB, STREXD, and STREXH are available in
ARMv6K and above."

Laurent