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aurdal@tree:~/Dev/OS$ make
nasm -f elf -o start.o start.asm
gcc -m32 -fno-stack-protector -fno-builtin -nostdinc -O -g -Wall -I. -c -o main.o main.c
gcc -m32 -fno-stack-protector -fno-builtin -nostdinc -O -g -Wall -I. -c -o scrn.o scrn.c
gcc -m32 -fno-stack-protector -fno-builtin -nostdinc -O -g -Wall -I. -c -o gdt.o gdt.c
ld -melf_i386 -nostdlib -N -Ttext 100000 -T link.ld -o kernel.bin start.o main.o scrn.o gdt.o
ld: warning: cannot find entry symbol start; defaulting to 0000000000100000
gdt.o: In function `gdt_install':
/aurdal/Desktop/Dev/gdt.c:77: undefined reference to `gdt_flush'
make: *** [kernel.bin] Error 1

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OUTPUT_FORMAT("binary")
ENTRY(start)
phys = 0x00100000;
SECTIONS
{
	.text phys : AT(phys) {
		code = .;
		*(.text)
		*(.rodata)
		. = ALIGN(4096);
	}
	.data : AT(phys + (data - code)) {
		data = .;
		*(.data)
		. = ALIGN(4096);
	}
	.bss : AT(phys + (bss - code)) {
		bss = .;
		*(.bss)
		. = ALIGN(4096);
	}
	end = .;
}

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; This is the kernel's entry point. We could either call main here,
; or we can use this to setup the stack or other nice stuff, like
; perhaps setting up the GDT and segments. Please note that interrupts
; are disabled at this point: More on interrupts later!
[BITS 32]
[global start]
start:
	mov esp, _sys_stack	 ; This points the stack to our new stack area
	jmp stublet
	
; This part MUST be 4byte aligned, so we solve that issue using 'ALIGN 4'
ALIGN 4
mboot:
	; Multiboot macros to make a few lines later more readable
	MULTIBOOT_PAGE_ALIGN	equ 1<<0
	MULTIBOOT_MEMORY_INFO	equ 1<<1
	MULTIBOOT_AOUT_KLUDGE	equ 1<<16
	MULTIBOOT_HEADER_MAGIC	equ 0x1BADB002
	MULTIBOOT_HEADER_FLAGS	equ MULTIBOOT_PAGE_ALIGN | MULTIBOOT_MEMORY_INFO | MULTIBOOT_AOUT_KLUDGE
	MULTIBOOT_CHECKSUM	equ -(MULTIBOOT_HEADER_MAGIC + MULTIBOOT_HEADER_FLAGS)
	EXTERN code, bss, end

	; This is the GRUB Multiboot header. A boot signature
	dd MULTIBOOT_HEADER_MAGIC
	dd MULTIBOOT_HEADER_FLAGS
	dd MULTIBOOT_CHECKSUM
	
	; AOUT kludge - must be physical addresses. Make a note of these:
	; The linker script fills in the data for these ones!
	dd mboot
	dd code
	dd bss
	dd end
	dd start

stublet:
	extern cmain
    call cmain
	jmp $


; Code for loading the GDT.
global gdt_flush   ; Allows the C code to link to this
extern gp            ; Says that '_gp' is in another file
gdt_flush:
    lgdt [gp]        ; Load the GDT with our '_gp' which is a special pointer
    mov ax, 0x10      ; 0x10 is the offset in the GDT to our data segment
    mov ds, ax
    mov es, ax
    mov fs, ax
    mov gs, ax
    mov ss, ax
    jmp 0x08:flush2   ; 0x08 is the offset to our code segment: Far jump!
flush2:
    ret               ; Returns back to the C code!

; Here is the definition of our BSS section. R
SECTION .bss
	resb 8192			   ; This reserves 8KBytes of memory here
_sys_stack: