Bochs 64-Bit Paging

[thepowersgang]

I'm starting on a 64-bit version of my OS and have succeeded in getting the 64-bit code executed but for some reason, even though all the paging structures are correct and in place, bochs only allows access to a 32-bit virtual address space. I've read through the Intel manuals and I presume that the AMD CPU uses the same structure in 64-bit mode so I am at a loss as to why it doesn't work.

When I execute "info tab" in the bochs debugging console while executing the 64-bit code I only get four entries: (these all point to the same range because I did that for to try and trace this bug/fault)

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0x00000000-0x003fffff -> 0x00000000-0x003fffff
0x40000000-0x403fffff -> 0x00000000-0x003fffff
0x80000000-0x803fffff -> 0x00000000-0x003fffff
0xc0000000-0xc03fffff -> 0x00000000-0x003fffff

Here is the NASM code for my paging structures:

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...
ALIGN 0x1000
_gpInitial_PML4:	; Page Map Level 4
	dq	_gpInitial_PDP + 3	; Identity Map Low 4Mb
	times 510 dq 0
	dq	_gpInitial_PDP + 3	; Also Map to 0xFFFF8000 00000000

_gpInitial_PDP:		; Page Directory Pointer Table
	times 512 dq _gpInitial_PD + 3
;	times 510 dq 0
;	dq _gpInitial_PD + 3

_gpInitial_PD:		; Page Directory
	dq _gpInitial_PT1 + 3
	dq _gpInitial_PT2 + 3
	times 510 dq 0

_gpInitial_PT1:		; Page Table 1
	%assign i 0
	%rep 512
	dq	i*4096+3
	%assign i i+1
	%endrep

_gpInitial_PT2:		; Page Table 2
	%assign i 512
	%rep 512
	dq	i*4096+3
	%assign i i+1
	%endrep

[JohnnyTheDon]

It does work with full 64-bit virtual address space. My kernel loads itself at 0xFFFF800000000000. Info tab is buggy and doesn't show anything above 4GB, but the area is still being mapped.

[JohnnyTheDon]

In addition...

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_gpInitial_PML4:   ; Page Map Level 4
   dq   _gpInitial_PDP + 3   ; Identity Map Low 4Mb
   times 510 dq 0
   dq   _gpInitial_PDP + 3   ; Also Map to 0xFFFF8000 00000000

Doesn't map at 0xFFFF800000000000. Change times 510 dq 0 to times 255 dq 0 and add times 255 dq 0 at the end of the PML4.

[thepowersgang]

Thank you very much!!!!


I cannot believe I missed that.