> On Oct 11, 2019, at 2:50 PM, Garrett D'Amore <garr...@damore.org> wrote: > > The issue is that you can't just arbitrarily throw a mutex out there -- you > have to have a place to *store* that, and you can't fit it inside the 64-bit > value. With a 64-bit ISA this isn't usually a problem, but with 32-bit ISAs > it is.
I'm not sure how this affects the compiler builtin atomics since they don't add mutexes. -- richard > > The only way to store the mutex (which could just be a spinlock) is to have > some other place that has it -- typically in library code. Allocation of > other objects like that normally falls outside the scope of a compiler > builtin (modulo bringing in a separate runtime object file, which can work > for user programs but generally not for kernels.) >> On 10/11/2019 11:38:57 AM, Richard Elling <richard.ell...@richardelling.com> >> wrote: >> >> >> >>> On Oct 9, 2019, at 11:41 AM, Garrett D'Amore <garr...@damore.org >>> <mailto:garr...@damore.org>> wrote: >>> >>> I don't think 32-bit compilers generally offer builtins for 64-bit atomics. >>> Frankly, they can't really unless the underlying ISA provides some >>> additional support for this in particular. >> >> Yes, that is why the builtins exist... the underlying ISA may have a method >> that is not part of the C language. >> >> Worst case, mutex protection will work... slowly. >> -- richard >> >>> >>> To implement a 64-bit atomic on a 32-bit architecture, you generally needs >>> some additional state somewhere -- typically some sort of mutex or >>> spinlock. That has to live somewhere. (You *might* be able to have a >>> compiler builtin that provides this along with a compiler runtime which >>> provides an instance of the spinlock somewhere in the program's data >>> section. I think this sort of "builtin" (which isn't really builtin at >>> all) generally can't be used in operating system kernels -- e.g. with >>> --freestanding.) >>>> On 10/9/2019 11:26:40 AM, Richard Elling <richard.ell...@richardelling.com >>>> <mailto:richard.ell...@richardelling.com>> wrote: >>>> >>>> If it is possible to specify a compiler version, it might be easier to use >>>> the compiler >>>> builtin atomics. Just sayin' >>>> -- richard >>>> >>>> >>>> ------------------------------------------ >>>> openzfs: openzfs-developer >>>> Permalink: >>>> https://openzfs.topicbox.com/groups/developer/T3ee8a81d5f09f2ec-Mabd6346845b79e16d16f57c2 >>>> >>>> <https://openzfs.topicbox.com/groups/developer/T3ee8a81d5f09f2ec-Mabd6346845b79e16d16f57c2> >>>> Delivery options: >>>> https://openzfs.topicbox.com/groups/developer/subscription >>>> <https://openzfs.topicbox.com/groups/developer/subscription> > > openzfs <https://openzfs.topicbox.com/latest> / openzfs-developer / see > discussions <https://openzfs.topicbox.com/groups/developer> + participants > <https://openzfs.topicbox.com/groups/developer/members> + delivery options > <https://openzfs.topicbox.com/groups/developer/subscription>Permalink > <https://openzfs.topicbox.com/groups/developer/T3ee8a81d5f09f2ec-Mb897f16441ee57856b4926b7> ------------------------------------------ openzfs: openzfs-developer Permalink: https://openzfs.topicbox.com/groups/developer/T3ee8a81d5f09f2ec-M51858eebfe98f256ff2d7f42 Delivery options: https://openzfs.topicbox.com/groups/developer/subscription
