Messages in this thread | | | Subject | Re: [PATCH 1/2] KVM: selftests: Make rseq compatible with glibc-2.35 | From | Gavin Shan <> | Date | Wed, 10 Aug 2022 10:37:40 +1000 |
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Hi Mathieu and Sean,
On 8/10/22 7:38 AM, Sean Christopherson wrote: > On Tue, Aug 09, 2022, Mathieu Desnoyers wrote: >> ----- On Aug 9, 2022, at 8:21 AM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote: >>> ----- Gavin Shan <gshan@redhat.com> wrote: >>>> On 8/9/22 5:16 PM, Florian Weimer wrote: >>>>>>> __builtin_thread_pointer doesn't work on all architectures/GCC >>>>>>> versions. >>>>>>> Is this a problem for selftests? >>>>>>> >>>>>> >>>>>> It's a problem as the test case is running on all architectures. I think I >>>>>> need introduce our own __builtin_thread_pointer() for where it's not >>>>>> supported: (1) PowerPC (2) x86 without GCC 11 >>>>>> >>>>>> Please let me know if I still have missed cases where >>>>>> __buitin_thread_pointer() isn't supported? >>>>> >>>>> As far as I know, these are the two outliers that also have rseq >>>>> support. The list is a bit longer if we also consider non-rseq >>>>> architectures (csky, hppa, ia64, m68k, microblaze, sparc, don't know >>>>> about the Linux architectures without glibc support). >>>>> >>>> >>>> For kvm/selftests, there are 3 architectures involved actually. So we >>>> just need consider 4 cases: aarch64, x86, s390 and other. For other >>>> case, we just use __builtin_thread_pointer() to maintain code's >>>> integrity, but it's not called at all. >>>> >>>> I think kvm/selftest is always relying on glibc if I'm correct. >>> >>> All those are handled in the rseq selftests and in librseq. Why duplicate all >>> that logic again? >> >> More to the point, considering that we have all the relevant rseq registration >> code in tools/testing/selftests/rseq/rseq.c already, and the relevant thread >> pointer getter code in tools/testing/selftests/rseq/rseq-*thread-pointer.h, >> is there an easy way to get test applications in tools/testing/selftests/kvm >> and in tools/testing/selftests/rseq to share that common code ? >> >> Keeping duplicated compatibility code is bad for long-term maintainability. > > Any reason not to simply add tools/lib/rseq.c and then expose a helper to get the > registered rseq struct? >
There are couple of reasons, not to share tools/testing/selftests/rseq/librseq.so or add tools/lib/librseq.so. Please let me know if the arguments making sense to you?
- By design, selftests/rseq and selftests/kvm are parallel. It's going to introduce unnecessary dependency for selftests/kvm to use selftests/rseq/librseq.so. To me, it makes the maintainability even harder.
- What selftests/kvm needs is rseq-thread-pointer.h, which accounts for ~5% of functionalities, provided by selftests/rseq/librseq.so.
- I'm not too much familiar with selftests/rseq, but it seems it need heavy rework before it can become tools/lib/librseq.so. However, I'm not sure if the effort is worthwhile. The newly added library is fully used by testtests/rseq. ~5% of that is going to be used by selftests/kvm. In this case, we still have cross-dependency issue.
I personally prefer not to use selftests/rseq/librseq.so or add tools/lib/librseq.so, but I need your feedback. Please share your thoughts. Thanks, Gavin
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