Wataru Ashihara <[email protected]> writes:
> On 2021/01/21 22:27, Philippe Mathieu-Daudé wrote: >> 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 <[email protected]> >>>>>>>>> --- >>>>>>>>> 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/[email protected]/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. >> >> > > Actually I use TCI also on macOS. Like the use case quoted by Philippe, > there're even other reasons to use TCI: > > 1. Learning TCG ops. Except it's only a subset of ops. Really interesting newer ones using the TCGv_vec types are entirely absent. > 2. Debugging QEMU with gdb. e.g. diagnose codegen or stepping into > helper functions from tci.c:tcg_qemu_tb_exec(). I do this quite often with TCG so I'm curious as to what the difference is here? > 3. Guest instruction tracing. TCI is faster than TCG or KVM when tracing > the guest ops [1]. I guess qira is using TCI for this reason [2]. How are you doing instruction tracing with TCG? Using the plugin interface? I think there probably is a roll for a *guest* interpreter given the amount of code that is translated only to be run once. However it would be a fairly large undertaking. > [1]: https://twitter.com/wata_ash/status/1352899988032942080 > [2]: https://github.com/geohot/qira/blob/v1.3/tracers/qemu_build.sh#L55 -- Alex Bennée
