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merlin



Joined: 17 Nov 2003
Posts: 11
merlin
Hi guys...
I have some problem with setting PAE.
As I see it these steps should do the work in case my code is in the first MB:
    Switch to PM
    Create PDPE
    Create PDE (one 2Mb page with 1:1 mapping)
    Set control registers W/O cr0
    Set CR0 with paging bit


Here is something that resembles my code
Code:
 ; Here I start in PM with a basic flat model
        mov     edi, PDPE_BASE
        mov     cr3, edi
        
        mov     eax, cr4
        or      eax, PAE_BIT
        mov     cr4, eax

        mov     eax, APP_PDE
        mov     ebx, eax
        shr     eax, 20
        shl     ebx, 12
        or      ebx, P_BIT
        stosd
        mov     eax, ebx
        stosd
        
        mov     ecx, 6
        xor     eax, eax
        rep     stosd
        
        mov     edi, APP_PDE
        xor     eax, eax
        or      eax, P_BIT + PS_BIT
        stosd
        xor     eax, eax
        stosd
        
        mov     ecx, 511*2
        xor     eax, eax
        rep     stosd

        mov     eax, cr0
        or      eax, PAGING_BIT
        mov     cr0, eax

; Do something
    


While "Do something" could probably be a far jump
or anything else that executes with paging mechanism
running (thats why 1:1 mapping), but anyway, with
this code it never reached.
Once paging bit is set everything goes to hell and crashes...

I do realize that I can set all those pages from RM,
and only then enable paging, without the need of 1:1
mapping, because paging wouldn't be really enabled untill
some far jump.
However, this should work also. Doesn't it?
Post 19 Sep 2006, 21:50
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merlin



Joined: 17 Nov 2003
Posts: 11
merlin
Problem solved (all PDPEs have to be peresent), topic closed...
Post 20 Sep 2006, 13:27
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Niels



Joined: 17 Sep 2006
Posts: 255
Niels
Hello merlin,

That particular problem seems to be Bochs related...

Intel,Page118: The present flag (bit 0) in the page-directory-pointer-table entries can be set to 0 or 1.
If the present flag is clear, the remaining bits in the PDPTE entry are available to the operating system.
Post 27 Sep 2006, 15:15
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