https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49244
--- Comment #18 from dhowells at redhat dot com <dhowells at redhat dot com> --- (In reply to Paolo Bonzini from comment #16) > > This also suggests there's an error in the current x86_64 kernel > > implementation > > as the kernel bitops are supposed to operate on machine word-size > > locations, so > > it should be using BTSQ not BTSL > > Why? Since bts adjust the memory address according to the bit number, btsl > and btsq are entirely the same instruction. Actually, no. BTSL takes a 32-bit bit number, whereas BTSQ takes a 64-bit bit number if I read the manual correctly. So, since test_and_set_bit() in the kernel takes a long bit number, BTSQ is the right thing to use. In practice, I don't imagine this is likely to be a real problem. I don't envision it as being likely that we will ever have a contiguous bitmap with >=2^31 bits in it.
