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Re: 64bit GNU Mach

From: Samuel Thibault
Subject: Re: 64bit GNU Mach
Date: Mon, 2 Apr 2012 14:39:05 +0200
User-agent: Mutt/1.5.21+34 (58baf7c9f32f) (2010-12-30)

Richard Braun, le Mon 02 Apr 2012 14:34:25 +0200, a écrit :
> On Mon, Apr 02, 2012 at 02:18:34PM +0200, Samuel Thibault wrote:
> > But then it needs some trick to convert to pointer everywhere needed.
> > Trying to manage low-4GiB allocation to avoid the trick would make
> > things nasty: remember that x86_64 does not have segmentation any more,
> > only flat addressing space, so we'd still need a 4GiB User/Kernel
> > separation, which was precisely what I wanted to avoid.
> I'm not following there. The conversion to pointer would be a simple
> lookup (changing all occurrences in the kernel can be tedious, agreed).

That's what I'm a bit reluctant to do.

> I don't see the relation with segmentation and the 4GiB split.

I said: "to avoid the trick", i.e. just use 32bit pointers, to just use
the same type as in userland as you suggested.

> What is the layout you expect for the kernel space ? First 4 GiB user
> then kernel ?

First 4GiB user, last 4GiB kernel.

> And you thought of segmentation to implicitely shift addresses ?

Again, there is no segmentation in x86_64.

> IMHO, changing GNU Mach to cleanly convert port names where needed
> remains the sane choice.

That is, use 32bit port names for userland, and convert to 64bit port
addresses for kernelland. But that can only work if using different


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