----- Gavin Shan <gshan@xxxxxxxxxx> wrote: > 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@xxxxxxxxxxxx> > > 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@xxxxxxxxxxxx> > > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> > > Link: https://lkml.kernel.org/r/20220124171253.22072-8-mathieu.desnoyers@xxxxxxxxxxxx > > > > 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. The registration is done by glibc initialization and thread startup code. > > I will come up something similiar for kvm/selftest/rseq. Make sure to chech the rseq selftests fixes recently pulled in the current merge window as well. One is relevant: https://github.com/torvalds/linux/commit/d1a997ba4c1bf65497d956aea90de42a6398f73a We may want to find a way to remove this duplicated rseq.c code eventually. Thanks, Mathieu > > Thanks, > Gavin > -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
