Messages in this thread | | | Subject | Re: tools/testing/selftests/kvm/rseq_test and glibc 2.35 | From | Gavin Shan <> | Date | Tue, 9 Aug 2022 11:47:43 +1000 |
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Hi Florian,
On 8/9/22 2:01 AM, Florian Weimer wrote: > It has come to my attention that the KVM rseq test apparently needs to > be ported to glibc 2.35. The background is that on aarch64, rseq is the > only way to get a practically useful sched_getcpu. (There's no hidden > per-task CPU state the vDSO could reveal as the CPU ID.) >
Yes, kvm/selftests/rseq needs to support glibc 2.35. The question is about glibc 2.34 or 2.35 because kvm/selftest/rseq fails on glibc 2.34
I would guess upstream-glibc-2.35 feature is enabled on downstream glibc-2.34?
# ./rseq_test ==== Test Assertion Failure ==== rseq_test.c:60: !r pid=112043 tid=112043 errno=22 - Invalid argument 1 0x0000000000401973: main at rseq_test.c:226 2 0x0000ffff84b6c79b: ?? ??:0 3 0x0000ffff84b6c86b: ?? ??:0 4 0x0000000000401b6f: _start at ??:? rseq failed, errno = 22 (Invalid argument) # rpm -aq | grep glibc-2 glibc-2.34-39.el9.aarch64
> The main rseq tests have already been adjusted via: > > commit 233e667e1ae3e348686bd9dd0172e62a09d852e1 > Author: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> > Date: Mon Jan 24 12:12:45 2022 -0500 > > selftests/rseq: Uplift rseq selftests for compatibility with glibc-2.35 > > glibc-2.35 (upcoming release date 2022-02-01) exposes the rseq per-thread > data in the TCB, accessible at an offset from the thread pointer, rather > than through an actual Thread-Local Storage (TLS) variable, as the > Linux kernel selftests initially expected. > > The __rseq_abi TLS and glibc-2.35's ABI for per-thread data cannot > actively coexist in a process, because the kernel supports only a single > rseq registration per thread. > > Here is the scheme introduced to ensure selftests can work both with an > older glibc and with glibc-2.35+: > > - librseq exposes its own "rseq_offset, rseq_size, rseq_flags" ABI. > > - librseq queries for glibc rseq ABI (__rseq_offset, __rseq_size, > __rseq_flags) using dlsym() in a librseq library constructor. If those > are found, copy their values into rseq_offset, rseq_size, and > rseq_flags. > > - Else, if those glibc symbols are not found, handle rseq registration > from librseq and use its own IE-model TLS to implement the rseq ABI > per-thread storage. > > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > Link: https://lkml.kernel.org/r/20220124171253.22072-8-mathieu.desnoyers@efficios.com > > But I don't see a similar adjustment for > tools/testing/selftests/kvm/rseq_test.c. As an additional wrinkle, > you'd have to start calling getcpu (glibc function or system call) > because comparing rseq.cpu_id against sched_getcpu won't test anything > anymore once glibc implements sched_getcpu using rseq. > > We noticed this because our downstream glibc version, while based on > 2.34, enables rseq registration by default. To facilitate coordination > with rseq application usage, we also backported the __rseq_* ABI > symbols, so the selftests could use that even in our downstream version. > (We enable the glibc tunables downstream, but they are an optional > glibc feature, so it's probably better in the long run to fix the kernel > selftests rather than using the tunables as a workaround.) >
Thanks for the pointer. It makes sense. So it means rseq registration has been done by glibc TLS? In this case, kvm/selftests/rseq is unable to register again.
I will come up something similiar for kvm/selftest/rseq.
Thanks, Gavin
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