Re: [RFC PATCH 2/2] gitlab-ci: Add a job building TCI with Clang

[Philippe Mathieu-Daudé]

On 1/21/21 1:02 PM, Daniel P. Berrangé wrote:
> On Thu, Jan 21, 2021 at 12:48:21PM +0100, Philippe Mathieu-Daudé wrote:
>> On 1/21/21 12:21 PM, Daniel P. Berrangé wrote:
>>> On Thu, Jan 21, 2021 at 12:18:18PM +0100, Philippe Mathieu-Daudé wrote:
>>>> On 1/21/21 11:32 AM, Daniel P. Berrangé wrote:
>>>>> On Thu, Jan 21, 2021 at 11:08:29AM +0100, Thomas Huth wrote:
>>>>>> On 10/01/2021 17.27, Philippe Mathieu-Daudé wrote:
>>>>>>> Split the current GCC build-tci job in 2, and use Clang
>>>>>>> compiler in the new job.
>>>>>>>
>>>>>>> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>>>>>>> ---
>>>>>>> RFC in case someone have better idea to optimize can respin this patch.
>>>>>>>
>>>>>>>   .gitlab-ci.yml | 22 ++++++++++++++++++++--
>>>>>>>   1 file changed, 20 insertions(+), 2 deletions(-)
>>>>>>
>>>>>> I'm not quite sure whether we should go down this road ... if we wanted 
>>>>>> to
>>>>>> have full test coverage for clang, we'd need to duplicate *all* jobs to 
>>>>>> run
>>>>>> them once with gcc and once with clang. And that would be just overkill.
>>>>>>
>>>>>> I think we already catch most clang-related problems with the clang jobs
>>>>>> that we already have in our CI, so problems like the ones that you've 
>>>>>> tried
>>>>>> to address here should be very, very rare. So I'd rather vote for not
>>>>>> splitting the job here.
>>>>>
>>>>> We can't possibly cope with the fully expanded matrix of what are
>>>>> theoretically possible combinations. Thus I think we should be guided
>>>>> by what is expected real world usage by platforms we target.
>>>>>
>>>>> Essentially for any given distro we're testing on, our primary focus
>>>>> should be to use the toolchain that distro will build QEMU with.
>>>>>
>>>>> IOW, for Windows and Linux distros our primary focus should be GCC,
>>>>> while for macOS, and *BSD, our focus should be CLang.
>>>>
>>>> Sounds good.
>>>>
>>>> Do we need a TCI job on macOS then?
>>>
>>> TCI is only relevant if there is no native TCG host impl.
>>>
>>> macOS only targets aarch64 and x86_64, both of which have TCG, so there
>>> is no reason to use TCI on macOS  AFAICT
>>
>> Yes, fine by me, but Wataru Ashihara reported the bug... ¯\_(ツ)_/¯
> 
> It doesn't look like they were using macOS - the message suggests
> Ubuntu host, and AFAIK, all Ubuntu architectures have support
> for TCG, so using TCI shouldn't have been required in the first
> place.
> 
> I guess we could benefit from a TCI job of some kind that uses
> CLang on at least 1 platform, since none exists.
> 
> This does yet again open up the question of whether we should be
> supporting TCI at all in this particular user's scenario though,
> since both KVM and TCG are available on Ubuntu x86 hosts already.

I understand Stefan envisions other use cases for TCI, which is
why it is still maintained. See:
https://www.mail-archive.com/qemu-devel@nongnu.org/msg461131.html

I agree with your previous comment:
> we should be guided by what is expected real world usage by
> platforms we target. Essentially for any given distro we're
> testing on, our primary focus should be to use the toolchain
> that distro will build QEMU with.

This rarely used config does not justify adding yet another CI job.

Thanks,

Phil.