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Posted: **Sat Feb 17, 2007 5:58 pm**

Hello,

Having been involved into OS development for almost a week now, I have finally reached the memory management part )
Parts present (thanks to the well-known tutorial) : GDT, IDT, IRQ0-1, simple shell, bootloader - GRUB.
The question is : how can I locate the start and the end of the kernel?
Linker source:

Code: Select all

OUTPUT_FORMAT("binary")
ENTRY(start)
phys = 0x00100000; /* 1 mb */
SECTIONS
{
  .text phys : AT(phys) {
    code = .;
    *(.text)
    . = ALIGN(0x1000);
  }
  .data : AT(phys + (data - code))
  {
    data = .;
    *(.data)
    . = ALIGN(0x1000);
  }
  .bss : AT(phys + (bss - code))
  {
    bss = .;
    *(.bss)
    . = ALIGN(0x1000);
  }
  end = .;
}

Is there a way to pass variables from linker to kernel? Would x=phys+SIZEOF(.text)+SIZEOF(.data)+SIZEOF(.bss) contain the address of the end of the kernel part?

Posted: **Sat Feb 17, 2007 6:37 pm**

just on the last line on kernel.asm add KERNEL_END: and after ORG add KERNEL_START, so just mov eax, KERNEL_START mov ebx, KERNEL_END and sub ebx, eax and EBX contains size of the kernel in bytes

Posted: **Sat Feb 17, 2007 6:40 pm**

the start of your kernel is at "code" and the end is at "end"

In C you would get the values like this:

Code: Select all

extern char code[];
extern char end[];

and to access them you would do something like:

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void *kStart = &code;
void *kEnd = &end;

In ASM you would just import "code" and "end"

EDIT: Hmm... not really sure if this will work for a binary...

Posted: **Sun Feb 18, 2007 5:53 am**

Thanks for the replies.
Figured out how to get size: simply pushed 'end' before calling main() so that I could access it as an argument.

Posted: **Sun Feb 18, 2007 8:25 am**

i hope you keep to the convention/prototype of main int main(int argc, char * argv[]), though it strictly not required it is nicer and deadmutex his method should also do the trick then again if it works it works.

OSDev.org

Determining the size of the kernel

Determining the size of the kernel