From: "ron minnich" <rminnich@gmail.com>
To: "Fans of the OS Plan 9 from Bell Labs" <9fans@cse.psu.edu>
Subject: Re: [9fans] double-mapping KZERO in l.s
Date: Wed, 22 Aug 2007 21:42:21 -0400 [thread overview]
Message-ID: <13426df10708221842v42de932dnd94b70868dcbf470@mail.gmail.com> (raw)
In-Reply-To: <39d464d9182fb939d449ead3c9f6fd90@quanstro.net>
On 8/22/07, erik quanstrom <quanstro@quanstro.net> wrote:
> where is that time? what i see in l.s
>
> MOVL $_startpg(SB), AX /* this is a virtual address */
> MOVL DX, CR0 /* turn on paging */
> JMP* AX /* jump to the virtual nirvana */
>
> perhaps i am missing it, but i don't see any point in the code
> where there's a problem. the two instructions that do the switch
> access only registers.
But the EIP has to access the instructions. After the mov, you're
still at low memory. Paging is turned on at this time. The JMP is
running at 0x10000something. So you turn paging on and do a jump, but
paging is on when you do the jmp and fetch from low memory. To make
the ifetch work you have to have the low map on.
I'll look at that code tonight again to make sure I'm not imaging
things, but I think this is right.
ron
next prev parent reply other threads:[~2007-08-23 1:42 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-08-22 21:51 erik quanstrom
2007-08-22 23:02 ` ron minnich
2007-08-22 23:44 ` erik quanstrom
2007-08-23 1:42 ` ron minnich [this message]
2007-08-23 1:54 ` erik quanstrom
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