David Daney writes: > Andrew Haley wrote: > > Phil Endecott writes: > > > David Daney wrote: > > > > Andrew Haley wrote: > > > >> Phil Endecott writes: > > > >> > Andrew Haley wrote: > > > >> > > this stuff really should be done by the compiler. > > > >> > > > > >> > Yes. I've filed a bug asking for a __sync_lock_test_and_set builtin: > > > >> > > > > >> > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33413 > > > >> > > > >> Surer, but the problem is that for most of the things we want to do > > > >> (lightweight locks, for example) __sync_lock_test_and_set() doesn't > > > >> really do what we need: we need compare_and_swap(). That's why the > > > >> kernel helper is so useful, because it's robust even if we are on > > > >> pre-ARMv6 hardware. > > > > > > > > Probably the enhancement request should be expanded to include *all* the > > > > __sync_* atomic memory primitives which includes compare_and_swap. > > > > > > No, because none of the others can be implemented without kernel > > > support or other magic. > > > > Yeah, I think that's right. Even in the case of post-v6 -- where it > > actually is possible to do this safely in userland -- if it's > > necessary to execute a bunch of instructions you might as well call a > > subroutine. > > There is nothing that says that __sync_compar_and_swap() cannot expand > to a libcall. Err, if a port doen't have an implementation, that's what gcc does anyway. :-) Andrew.
