On Mon, Nov 04, 2024 at 12:32:40PM +0100, Peter Zijlstra wrote: > On Sat, Nov 02, 2024 at 10:58:42PM +0100, Florian Weimer wrote: > > > QEMU hints towards further problems (in linux-user/syscall.c): > > > > case TARGET_NR_set_robust_list: > > case TARGET_NR_get_robust_list: > > /* The ABI for supporting robust futexes has userspace pass > > * the kernel a pointer to a linked list which is updated by > > * userspace after the syscall; the list is walked by the kernel > > * when the thread exits. Since the linked list in QEMU guest > > * memory isn't a valid linked list for the host and we have > > * no way to reliably intercept the thread-death event, we can't > > * support these. Silently return ENOSYS so that guest userspace > > * falls back to a non-robust futex implementation (which should > > * be OK except in the corner case of the guest crashing while > > * holding a mutex that is shared with another process via > > * shared memory). > > */ > > return -TARGET_ENOSYS; > > I don't think we can sanely fix that. Can't QEMU track the robust thing > itself and use waitpid() to discover the thread is gone and fudge things > from there? Hmm, what about we mandate 'natural' alignement of the structure such that it is always inside a single page, then QEMU can do the translation here and hand the kernel the 'real' address.
