Re: Paging problems
Posted: Sat Jun 17, 2017 2:38 am
As to your first point, I'll do an "info reg" at _start to try to work out what's happening. On the point that you mentioned in your edit, I can't believe that I didn't notice that.
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Re: Paging problems
Posted: Sat Jun 17, 2017 2:49 am
It is also worthwhile to check the calling convention between boot32.s (which is compiled as code32) and paging.cpp (which is compiled as code64), as it applies when calling page_set.
Re: Paging problems
Posted: Sat Jun 17, 2017 3:25 am
head... meet desk.
I am SUCH and IDIOT. Why did I not think to specify gcc to compile those bits of code as 32-bit I have no idea.
I am SUCH and IDIOT. Why did I not think to specify gcc to compile those bits of code as 32-bit I have no idea.
Re: Paging problems
Posted: Sat Jun 17, 2017 6:39 am
I think I realized the situation a bit late 
.
A 32bit cpu, interpreting actual 64bit instructions as 32bit, seems to be the cause, unless something else turns up as the root cause for the weird behaviour.
. A 32bit cpu, interpreting actual 64bit instructions as 32bit, seems to be the cause, unless something else turns up as the root cause for the weird behaviour.
Re: Paging problems
Posted: Sat Jun 17, 2017 6:06 pm
Not quite. A 64-bit cpu, running what should be 32-bit instructions as 64-bit, while in protected(32-bit) mode.
Re: Paging problems
Posted: Sun Jun 18, 2017 9:23 pm
Well. I managed to get my paging problem fixed by setting the page tables in my boot32.s file. Now I need to set the GDT. Can anyone translate this to AT&T assembly:
Code: Select all
GDT64: ; Global Descriptor Table (64-bit).
.Null: equ $ - GDT64 ; The null descriptor.
dw 0 ; Limit (low).
dw 0 ; Base (low).
db 0 ; Base (middle)
db 0 ; Access.
db 0 ; Granularity.
db 0 ; Base (high).
.Code: equ $ - GDT64 ; The code descriptor.
dw 0 ; Limit (low).
dw 0 ; Base (low).
db 0 ; Base (middle)
db 10011010b ; Access (exec/read).
db 00100000b ; Granularity.
db 0 ; Base (high).
.Data: equ $ - GDT64 ; The data descriptor.
dw 0 ; Limit (low).
dw 0 ; Base (low).
db 0 ; Base (middle)
db 10010010b ; Access (read/write).
db 00000000b ; Granularity.
db 0 ; Base (high).
.Pointer: ; The GDT-pointer.
dw $ - GDT64 - 1 ; Limit.
dq GDT64 ; Base.
Re: Paging problems
Posted: Mon Jun 19, 2017 12:21 am
Would it not be better to understand what the bits and pieces of such a table mean, and then write one of your own directly in your desired assembly?
Re: Paging problems
Posted: Mon Jun 19, 2017 7:30 pm
For the most part, it was only the offset sections, "equ $ - GDT64" that got me. I managed to figure most of it out.
My only remaining question is if I need to use $GDT64 instead of GDT64 in .pointer?
Edit: I did just realize that I couldn't use ".Code" or ".Data" for the GDT offsets because they might be assembled weirdly.
Edit 2: Okay, for some reason, when I try to set my data segment, it jumps to an entirely different area. Weird.
Code: Select all
GDT64:
.Null = . - GDT64
.short 0
.short 0
.byte 0
.byte 0
.byte 0
.byte 0
.Code = . - GDT64
.short 0
.short 0
.byte 0
.byte 0x9A
.byte 0x20
.byte 0
.Data = . - GDT64
.short 0
.short 0
.byte 0
.byte 0x92
.byte 0
.byte 0
.Pointer:
.short = . - GDT64 - 1
.quad GDT64
Edit: I did just realize that I couldn't use ".Code" or ".Data" for the GDT offsets because they might be assembled weirdly.
Edit 2: Okay, for some reason, when I try to set my data segment, it jumps to an entirely different area. Weird.