Messages in this thread | | | Date | Sun, 04 Nov 2007 15:07:49 -0800 | From | Jeremy Fitzhardinge <> | Subject | Re: [PATCH] fix i486 boot failure due to stale %ds |
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Mikael Pettersson wrote: > On Sun, 04 Nov 2007 11:41:58 -0800, H. Peter Anvin wrote: > >> Mikael Pettersson wrote: >> >>> First patch didn't build. Second patch builds and boots Ok. >>> >>> So this means the 486 DX4 has a buggy mov to %cr0? >>> >>> >> Apparently. >> > > Maybe not. I had a look in Intel's SDM Vol3, and the > section "switching to protected mode" specifies that > a move to %cr0 that sets PE should immediately be > followed by a far jmp or call. >
Yes, that's what the spec says. I queried this a few months ago, but hpa used his convincing voice and said that in practice it isn't necessary; there are no known cpus which need this, and any that do would cause other things to break. But I guess now we have the counter-example...
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