Sending Parameters to Kernel?

[elderK]

Hey all.
I have a question.
... How can I Send a Parameter to my Kernel?
Id like to send it the Amount of Memory my system has.

This is the later code... in teh Bootloader. JUST before it calls the Kernel.

    lgdt [citadel_gdt_descriptor]      ; Load the Global Descriptor Table.

    mov eax, cr0       ; Enable PE Bit in CR0

    or eax, 1    

    mov cr0, eax
   
      mov eax, 0x09
      push eax
    jmp 0x08:clear_pipe       

Id like to know how to pass it a Number, that being the Number of RAM I have.

Ive tried moving a valu einto EAX and pushing EAX, but nothing happens.


Any advice would be helpful.
Thanks!

[Tolga]

Hmm. Example, eax is including memory size.

----- asm file -----------
...
; Enter protected mode
mov ebx, eax
mov eax, cr0
or al, 1
mov cr0, eax
...
...
; Copy memory size
mov eax, ebx
mov esi, 0x100
mov [esi], eax

-----------------------------

In kernel, you can read 0x100 in your C kernel.

[dc0d32]

;setting up cr0, flushing prefetch q etc

;assuming mem in ebx, lets say

pushl %ebx
jmp cmain


and the cmain should be defined like

.... cmain(unsigned int ram_available){...}

make sure you dont declare cmain as gcc attribute regparm.


but the better way around is to use GRUB, and use the map it provides. in that case, you just have to save one pointer in asm code into some global variable, which you can use in your c code later on. and, afaik, the memory map is quite reliable and i dont find many reasons why you should care about counting the RAM all by yourself.

[Ryu]

I also use the stack to send my kernel the current memory map. Make sure that when your in protected mode that you set up ss selector and esp accordingly with the real mode setting. For me I used a 80:800h (linear 1000h) stack in real mode, and in protected mode I use a zero based data selector and code selector (for now anyways). That means I would have to add 800h to esp (not resetting it) and load ss to the data selector. After it is okay to start popping.