lkml.org 
[lkml]   [2007]   [Nov]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [GIT PULL] x86 setup: correct booting on 486DX4


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!)

Linus
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-11-05 00:29    [W:0.058 / U:1.376 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site