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Re: [bug #17346] GNU mach can't handle 4GB memory

From: Samuel Thibault
Subject: Re: [bug #17346] GNU mach can't handle 4GB memory
Date: Mon, 20 Nov 2006 15:10:36 +0100
User-agent: Mutt/1.5.11

Constantine Kousoulos, le Mon 20 Nov 2006 17:01:14 +0200, a écrit :
> Samuel Thibault wrote:
> >Constantine Kousoulos, le Mon 20 Nov 2006 16:27:07 +0200, a écrit :
> >>Oops wrong copy-paste. Correct my previous email with this:
> >>
> >>... Mach's virtual address space is 4 GB big according to this 
> >>entry in gnumach/i386/i386/vm_param.h: #define 
> >>LINEAR_MAX_KERNEL_ADDRESS   ((vm_offset_t) 0xffffffff) ...
> >
> >Nope, that's just the upper limit. And since the lower limit is 
> >#define LINEAR_MIN_KERNEL_ADDRESS       ((vm_offset_t) 0xc0000000)
> >that makes 1GB.
> >
> Doesn't Mach use at all virtual addresses from 0x00000000 to 
> 0xc0000000?

No: 0x00000000-0xbfffffff is used by user space.

BTW, don't mix linear space and virtual space. In the virtual space
(only paging is applied, not segmenting), kernel resides between
0x00000000 and 0x3fffffff. In linear space (with both paging and
segmenting), the kernel space is shifted up to 0xc0000000-0xffffffff,
letting room for user space between 0x00000000 and 0xbfffffff


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