On Mon, 14 Jan 2002, Kevin D. Kissell wrote: > Careful, Dom. As far as user-mode programs are concerned, > older 64-bit MIPS designs (R4xxxx/R5xxxx/R7xxxx), one cannot > enable 64-bit arithmetic without enabling 64-bit addressing, > both of these functions being enabled by the Status.UX bit. > SGI's IRIX OS allowed an execution model that provided > 64-bit registers and math, while *simulating* a 32-bit address > space, based on sign-extending 32-bit addresses to 64-bits. > The user was spared doubling the footprint of all his pointers, > but the OS still had to manage the larger page tables. Note that there is usually no point in using a 64D/32A mode unless you have weird toolchain problems. You may get a 64D/32A user program by mapping its segments appropriately in the 31-bit address space. Since the MIPS user segment always starts at zero such a program won't see a difference between a 64D/32A and a 64D/64A mode. Why would an OS need larger page tables? -- + Maciej W. Rozycki, Technical University of Gdansk, Poland + +--------------------------------------------------------------+ + e-mail: macro@ds2.pg.gda.pl, PGP key available +
