On 26/06/17 09:37, Toebs Douglass wrote: > Hej all. > > __GCC_HAVE_SYNC_COMPARE_AND_SWAP_16 is defined on x86_64 if and only if > -mcx16 is given. > > gcc version 4.9.2 (Debian 4.9.2-10) > winterflaw@localhost:~$ gcc -march=native -dM -E - < /dev/null | sort | > grep SYNC > #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_1 1 > #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_16 1 > #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_2 1 > #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 1 > #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_8 1 Stunning, eh? what happened was; without -march=native, there's no SYNC_16. This isn't too surprising, I think, because looking over the list of predefines (and configure options) the compiler actually seems to have no default arch - I mean, it must, but there are no defines indicating it. Lord knows what it's assuming, since the i586 introduced DWCAS on Intel. Even with that seeming lack of arch, with -mcx16, we do of course then get SYNC_16, since we've told the compiler it exists. If I then move to arch native, I get SYNC_16 even without mcx16; this on 4.9.2. That surprised me (and is the cause of the mistake in the original post). Anyways, this wasn't the main point - it was only there to point out SYNC_16 is set on x86_64 (usually). > __GCC_HAVE_SYNC_COMPARE_AND_SWAP_16 is not defined at all on aarch64, as > far as I can tell. > > gcc version 4.9.2 (Debian/Linaro 4.9.2-10) > debian@pine64:~$ gcc -march=armv8-a+crypto+crc -dM -E - < /dev/null | > sort | grep SYNC > #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_1 1 > #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_2 1 > #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 1 > #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_8 1 This being the main point.
