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I'm currently setting up page frame allocation. For that purpose i got a memory map from grub.
It gave me 2 usable chunks of memory
base 0x0 length 0x9fc00
base 0x100000 length 0x7efe000
but my kernel's code & data is inside of the second chunk.
My question is: how do i know which space is "occupied"? So how to find out how much memory my kernels code&data use?
Of course i could reserve an arbitrary amount of memory "just to be sure" but what if my kernel ever exceeds this point?
To solve this i would need a pointer to "the end" of my kernel. How to do this?

Thanks in advance. Every advice is welcome

Your elf files tell you how big the various sections are, so you know how much memory the kernel uses.

Thank you, i haven't thought about this.
I'll have a look inside the specification

Does GRUB load my ELF directly at 0x100000?

For a pointer to the end of your code placeat the end of the .bss section of your linker script. If you then useyou get a pointer to the end of your kernel.
P.S.
This is explained in more detail at the wiki (http://wiki.osdev.org/Writing_A_Page_Frame_Allocator).
P.P.S.
Don't use the article for your actual allocator, it is basically a stub.

Thank you. You really helped me alot!