Messages in this thread | | | From | "H. Peter Anvin" <> | Subject | Re: [patch] 2.4.0-test2: %cr4 in a register dump | Date | 5 Jul 2000 13:23:27 -0700 |
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Followup to: <Pine.LNX.4.10.10007051307000.831-100000@penguin.transmeta.com> By author: Linus Torvalds <torvalds@transmeta.com> In newsgroup: linux.dev.kernel > > > > this is aesthetically bogus. i think you should always print CR4, > > no matter whether it's 0 or not. > > If I remember correctly, there are CPU's out there that will bomb out > horribly when you access %cr4 if the register doesn't exist. >
They will #GP, yes. If you want to read %cr4 unconditionally you have to be prepared to trap the #GP.
> > Do I remember wrong? > > I'd certainly agree with printing out cr4 even if it would be zero, I just > disagree very much with adding a register read to the dump output that may > cause an infinite regression of traps.. >
Indeed. %cr4 was introduced in the P5; I believe it is probably a valid assumption that if the CPU has CPUID it also has %cr4 (the later 486's which had CPUID also had VME, so they must have supported %cr4.)
-hpa
-- <hpa@transmeta.com> at work, <hpa@zytor.com> in private! "Unix gives you enough rope to shoot yourself in the foot." http://www.zytor.com/~hpa/puzzle.txt
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