rcd@ico.isc.com (Dick Dunn) (02/17/91)
sef@kithrup.COM (Sean Eric Fagan) writes: > james@bigtex.cactus.org (James Van Artsdalen) writes: > >there is no > >reason for 387 support (real or emulated) to need the u block to be > >writable. > Yes, there is, unless you want to make the emulated fpu even slower. [Sean goes on to describe that the FP emulator runs in user state, for good reasons, and state switches are costly--you don't want to go through a protection-state transition in the coprocessor trap call gate.] While Sean's reasoning is correct as far as it goes, Van Artsdalen's point still holds. While you probably do need to keep the emulated FP registers in the u-area (that's the logical place, and I don't know where else you could put them safely), you don't need to have the "vulnerable" part of the u-area in the same page as the FP registers. Put the FP registers in a writable page; put the goodies in a non-writable page. -- Dick Dunn rcd@ico.isc.com -or- ico!rcd Boulder, CO (303)449-2870 ...But is it art?