----- On Apr 12, 2018, at 4:23 PM, Andi Kleen a...@firstfloor.org wrote: >> Can we plan on merging just the plain rseq parts *without* this all >> first, and then see the cpu_opv thing as a "maybe future expansion" >> part. > > That would be the right way to go. I doubt anybody really needs cpu_opv. > We already have other code (e.g. vgettimeofday) which cannot > be single stepped, and so far it never was a problem.
Single-stepping is only a subset of the rseq limitations addressed by cpu_opv. Anoher major limitation is algorithms requiring data migration between per-cpu data structures safely against CPU hotplug, and without having to change the cpu affinity mask. This is the case for memory allocators and userspace task schedulers which require cpu_opv for migration between per-cpu memory pools and scheduler runqueues. About the vgettimeofday and general handling of vDSO by gdb, gdb's approach only takes care of line-by-line single-stepping by hiding Linux' vdso mapping so users cannot target source code lines within that shared object. However, it breaks instruction-level single-stepping. I reported this issue to you back in Nov. 2017: https://lkml.org/lkml/2017/11/20/803 Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com