Michael Uhler wrote: > > On Mon, 2003-09-29 at 10:31, Finney, Steve wrote: > > What would be the downside to enabling 64 bit operations in user space on a 32 bit kernel (setting the PX bit in the status register?). The particular issue is that I want to access 64 bit-memory mapped registers, and I really need to do it as an atomic operation. I tried borrowing sibyte/64bit.h from the kernel, but I get an illegal instruction on the double ops. > > > The most glaring problem is you violate the rule that the 64-bit GPRs > are sign-extended when running a 32-bit binary. There are all kinds > of assumptions in the hardware and software that depend on the > GPRs being sign-extended, and to violate this will risk some > serious instability of the software. Not to mention that the kernel won't preserve the upper 32 bits across interrupts and system calls, if you even manage to get 64-bit values in the registers in the first place. Kip
