Messages in this thread | | | Date | Sun, 4 Nov 2007 15:25:06 -0800 (PST) | From | Linus Torvalds <> | Subject | Re: [GIT PULL] x86 setup: correct booting on 486DX4 |
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On Sun, 4 Nov 2007, Linus Torvalds wrote: > > I'm not entirely sure that it needs to be a long-jump, btw. I think any > regular branch is sufficient. You obviously *do* need to make the long > jump later (to reload %cs in protected mode), but I'm not sure it's needed > in that place. I forget the exact rules (but they definitely were > documented).
Hmm. The original Linux code did
movw $1, %ax lmsw %ax jmp flush_instr flush_instr:
and I think that was straigh out of the documentation. So yeah, I think that's the right fix - not a longjmp (which in itself is dangerous: it potentially behaves *differently* on different CPU's, since some CPU's may do the long jump with pre-protected-mode semantics, while others will do it with protected mode already in effect!)
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