On 2020-03-08 20:59, Eliot Moss wrote: > On 3/8/2020 10:29 PM, Eliot Moss wrote: >> This is probably to the gcc maintainer ... >> >> I am running on a processor that has compare/exchange 128-bit (cx16 >> capability), >> and I compiler with -mcx16 and -latomic. I'm on the latest release cygwin >> gcc >> (9.2.0-3, I believe) and the corresponding libatomic. I have a program with >> this in it: >> >> __atomic_compare_exchange((__int128 *)&s1, (__int128 *)&z, (__int128 *)&s2, >> 0, >> __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST); >> >> This compiles to a call (nice if it would inline, but ...) to >> __atomic_compare_exchange_16, which uses mutex's, not the CMPXCHG16B >> instruction I was hoping for. Note I am doing dynamic linking, >> which on at least one other platform results in dynamic selection >> of a lib_at implementation of the compare/exchange, which does use >> the desired instruction. >> >> Is this a limitation of cygwin gcc, or should I be doing something >> different to achieve the desired effect? >> >> Obviously it would be best not to going an asm inline if I can avoid it, >> but I suppose I can dig into the libatomic source to get the right >> incantation for it if need be ... > > A quick followup: I was able to get __sync_val_compare_and_swap_16 to work > (and its bool form). That will do for now, though of course it's deprecated.
You just needed to go to the next info page: $ info gcc __atomic and use: #include <stdatomic.h> extern bool __atomic_compare_exchange ( TYPE *ptr, TYPE *expected, TYPE *desired, bool weak, int success_memorder, int failure_memorder); or higher level macro: atomic_compare_exchange_strong(PTR, VAL, DES) defined in /lib/gcc/x86_64-pc-cygwin/*/include/stdatomic.h -- Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada This email may be disturbing to some readers as it contains too much technical detail. Reader discretion is advised. -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple