Paging

[chrisa128]

It is 0 in the GDT for the data selector. and it still triple faults on me. The ASM functions are as follow...

Code: Select all

[GLOBAL _get_page_bit]
_get_page_bit
   mov eax,cr0
   retn

[GLOBAL _set_page_bit]
_set_page_bit
   push eax      
      mov eax,[esp + 8]
      mov cr0,eax
   pop eax
   jmp check1
check1:
   retn

[GLOBAL _get_page_dir]
_get_page_dir
   mov eax,cr3
   retn

[GLOBAL _set_page_dir]
_set_page_dir
   pusha
   push eax      
      mov eax,[esp + 4]
      mov cr3,eax
   jmp check2
check2:
   pop eax
   popa
   retn 

[distantvoices]

Try this nasm-code. After all, it worked fine for me, is simple and straight forward:

[global activate_paging]
;void activate_paging(ulong_t *page_directory)->c prototype
cli
push ebp
mov ebp,esp
mov eax,[ebp+8]
mov cr3,eax
mov eax,cr0
or eax,0x80000000
mov cr0,eax
jmp s1
s1:
pop ebp
sti
ret

this you call it in c:
activate_paging(pgdir)

[chrisa128]

It works or if doesn't I am blind!!!

My Thanks to...

beyond infinity
aafuss
pype.clicker
and anyone else who helped as I am doing this from memory

[Pype.Clicker]

afai can see, your problem (as you probably figured out now ;p ) was in the ASM-C parameters passing.

It might be impressive to see code where arguments are addressed with [esp+xxx], but in fact it isn't. It's just more complicated to handle.

A C-function always starts with

Code: Select all

push ebp
mov ebp,esp

This rule allows implementing a stack-tracing algorithm very simply. It also means that the arguments of the function will always be at the same location (arg1 = [ebp+8], arg2=[ebp+12], arg3=[ebp+16] -- [ebp+4] is the return location)

if you want to push/pop other registers, do it *after* you set ebp=esp.

you can also quickly restore the stack to a clean value (even if you had some misbehaved push/pop) with mov esp,ebp ; pop ebp.

May the Stack be with You

[chrisa128]

Thanks pype, I will remeber this in future but during the course of getting paging going I have learnt plenty.

Now on to getting malloc and free written!!!