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

[Philippe Mathieu-Daudé]

On 06/27/2018 10:03 AM, Alex Bennée wrote:
> 
> Daniel P. Berrangé <address@hidden> writes:
> 
>> On Wed, Jun 27, 2018 at 09:57:09AM +0200, Markus Armbruster wrote:
>>> Thomas Huth <address@hidden> writes:
>>>
>>>> On 27.06.2018 08:51, Gerd Hoffmann wrote:
>>> [...]
>>>>> Drop support for 32bit hosts in qemu?
>>>>
>>>> I guess the only way to answer that question reliably is to send a patch
>>>> to mark 32-bit hosts as deprecated...
>>>>
>>>> Anyway, you still have got to fix that problem with -m32 now somehow
>>>> since we certainly can not drop 32-bit immediately.
>>>
>>> We certainly can if we want to.
>>>
>>> Our formal deprecation policy codifies our compromise between the need
>>> to evolve QEMU and the need of its users for stable external interfaces.
>>>
>>> "Compiles on host X" is also a need, but it's a different one.
>>> Evidence: "Supported build platforms" has its own appendix, separate
>>> from "Deprecated features".  It's mum on 32-bit hosts.
>>
>> It is silent on host architecture coverage in general in fact. It was
>> only really focusing on operating systems and so any arch coverage is
>> at best inferred from what those OS target. Fedora covers 32-bit & 64-bit
>> arches for example, so you could take that to imply we need to support
>> both in QEMU.
>>
>> It is fuzzier though because while Peter has good OS coverage for his
>> merge testing, I don't think he has full host arch coverage for everything
>> that downstreams expect QEMU to build on ?
> 
> We do however have cross build infrastructure for all tcg/foo backends.
> They are run by the shippable CI framework (which is how I noticed):
> 
>   https://app.shippable.com/github/qemu/qemu/runs?branchName=master

FWIW we can also build ppc32 again (with the apt-fake kludge although).

> 
> Once we have the changes made to the wiki I'd like to use:
> 
>   https://wiki.qemu.org/Template:CIStatus
> 
> In a few choice places on the wiki, including the front page, for better
> visibility.
> 
>>> I'm not saying we *should* drop 32-bit hosts immediately.  Only that the
>>> feature deprecation policy does not apply.
>>>
>>> Is QEMU still useful on 32-bit hosts?  Honest question!
>>
>> That answer varies depending on what you're using QEMU for I think. It
>> could be that people see tools like qemu-img/qemu-nbd as useful even
>> if they don't use system emulators. And of course userspace emulators
>> are enough distinct use case.
>>
>> IMHO as long as distros are shipping 32-bit support, it is reasonable
>> to assume there will be people who find QEMU useful to some degree.
>>
>> Personally I don't have any need for 32-bit hosts, but clearly some
>> people do since otherwise distros would  have killed their 32-bit
>> arches already.
> 
> I know of at least one kernel developer who uses qemu-system-aarch64 on
> their 32 bit ARM Chromebook to test their 64 bit code. Next time I see
> them I'll see if they are still using it.
> 
> My feeling is although probably not widespread it certainly can be handy.
> 
>>
>> Regards,
>> Daniel
> 
> 
> --
> Alex Bennée
>