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On Tue 2018-06-12 12:31:24, Mathieu Desnoyers wrote: > ----- On Jun 12, 2018, at 9:11 AM, Florian Weimer fweimer@redhat.com wrote: > > > On 06/11/2018 10:04 PM, Mathieu Desnoyers wrote: > >> ----- On Jun 11, 2018, at 3:55 PM, Florian Weimer fweimer@redhat.com wrote: > >> > >>> On 06/11/2018 09:49 PM, Mathieu Desnoyers wrote: > >>>> It should be noted that there can be only one rseq TLS area registered per > >>>> thread, > >>>> which can then be used by many libraries and by the executable, so this is a > >>>> process-wide (per-thread) resource that we need to manage carefully. > >>> > >>> Is it possible to resize the area after thread creation, perhaps even > >>> from other threads? > >> > >> I'm not sure why we would want to resize it. The per-thread area is fixed-size. > >> Its layout is here: include/uapi/linux/rseq.h: struct rseq > > > > Looks I was mistaken and this is very similar to the robust mutex list. > > > > Should we treat it the same way? Always allocate it for each new thread > > and register it with the kernel? > > That would be an efficient way to do it, indeed. There is very little > performance overhead to have rseq registered for all threads, whether or > not they intend to run rseq critical sections. People with slow / low memory machines would prefer not to see overhead they don't need... > I have a few possible approaches in mind (feel free to suggest other > options): > > A) glibc exposes a strong __rseq_abi TLS symbol: > > - should ideally *not* be global-dynamic for performance reasons, > - registration to kernel can either be handled explicitly by requiring > application or libraries to call an API, or implicitly at thread > creation, ...so I'd prefer explicit API call. > B) librseq.so exposes a strong __rseq_abi symbol: Works for me. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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