On 10 June 2011 20:38, Nicolas Pitre <nicolas.pi...@linaro.org> wrote: > On Fri, 10 Jun 2011, David Gilbert wrote: > >> On 25 May 2011 04:45, Nicolas Pitre <nicolas.pi...@linaro.org> wrote: >> >> <snip> >> >> > FWIW, here's what the kernel part might look like, i.e. for >> > compatibility with pre ARMv6k systems (beware, only compile tested): >> >> <snip> >> >> Hi Nicolas, >> I've just about got a set of gcc backend changes working for the inline >> case >> and plan on attacking libgcc next week. >> >> What are your intentions for that code that you sent in this message - do >> you intend to finish it off and upstream it or were you wanting me to do that >> as part of this task? > > I'll refine it and push it upstream.
OK, thanks. > >> If you're doing it could you confirm the interface to work to. > > Here it goes: > > * Reference prototype: > * > * int __kernel_cmpxchgd64(const int64_t *oldval, > * const int64_t *newval, > * volatile int64_t *ptr); > * > * Input: > * > * r0 = pointer to oldval > * r1 = pointer to newval > * r2 = pointer to target value > * lr = return address > * > * Output: > * > * r0 = returned value (zero or non-zero) > * C flag = set if r0 == 0, clear if r0 != 0 > * > * Clobbered: > * > * r3, condition flags OK <snip> > * - This call is valid only if __kernel_helper_version >= 5. > > Of course, as discussed, this would be preferable if the interface in > libgcc was in a separate object file so any reference to it would also > bring in a global constructor from which the __kernel_helper_version > value could be verified in order to prevent usage of this interface on > kernels that lack it. I was thinking of looking at ifunc for this;but I've not looked yet. >> Also, do you think there should be a halfword and byte interface as well, >> given that halfword and byte ldrex implementations aren't available on >> older ARMs, >> or expect user space to do a bit of mask fiddling with the 32bit ones? > > It is indeed better if user space deals with it using the 32-bit > interface. I'd prefer adding new kernel helpers only when absolutely > required. Actually, I've found Julian Brown already implemented that in user space in 2008 (see gcc/config/arm/linux-atomic.c) Dave _______________________________________________ linaro-dev mailing list linaro-dev@lists.linaro.org http://lists.linaro.org/mailman/listinfo/linaro-dev
