boot.s

.set ALIGN,    1<<0                 // align loaded modules on page boundaries
.set MEMINFO,  1<<1                 // provide memory map
.set FLAGS,    ALIGN | MEMINFO      // this is the Multiboot 'flag' field
.set MAGIC,    0x1BADB002           // 'magic number' lets bootloader find the header

.set CHECKSUM, -(MAGIC + FLAGS)     /* checksum of above, prevents code from accidentally
                                       being loaded as kernel */

/*
 * Implements the multiboot standard
 * GRUB looks for this when bootloading.
 */
.section .multiboot
    .align  4
    .long   MAGIC
    .long   FLAGS
    .long   CHECKSUM

// Stack
.section .bss
    .align  16
    stack_bottom:
        .skip   16384 # 16 KiB
    stack_top:

.text
.globl _start

/*
 * _start is the designated function signature
 * for starting the kernel via GRUB.
 */
_start:
    /*
     * GRUB does not initialize the stack, must
     * be done manually.
     */
    mov     $stack_top, %esp

	  call    kernel_entry

    /*
     * Do nothing.Prevents the kernel from stopping
     * abruptly.
     */
l:	jmp   l

.size _start, . - _start