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. Andrew.
