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void kernel_main(struct multiboot_info *mbt, unsigned int magic) {

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.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, to prove we are multiboot



.section .multiboot
.align 4
.long MAGIC
.long FLAGS
.long CHECKSUM

.section .bootstrap_stack, "aw", @nobits
stack_bottom:
.skip 16384         #16 KiB
stack_top:

.section .text
.global _start
.type _start, @function
_start:
   
    movl $stack_top, %esp

    sti
    pushl %eax       # EAX contains the Magic Number returned by Grub <-- THIS IS WHERE IT GOT 0x2BADB0FF
    pushl %ebx       # EBX contains a pointer to the multiboot info structure.
    call kernel_main

halt:
    cli
    hlt
.Lhang:
    jmp .Lhang

.section .text
.global pause
.type pause @function
pause:
    hlt
    ret

.section .text
.global sys_cli
.type sys_cli @function
sys_cli:
    hlt
    ret


.section .text
.global sys_sti
.type sys_sti @function
sys_sti:
    hlt
    ret

.size _start, . - _start

.section .kend
.global end_of_kernel
end_of_kernel:

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...
#define MULTIBOOT_MAGIC_NUMBER 0x2BADB002
...
void kernel_main(struct multiboot_info *mbt, unsigned int magic) {
  ...
  printf("magic number fail. expected: %x got: %x\n", MULTIBOOT_MAGIC_NUMBER, magic); # magic = 0x2BADB0FF
  ...
}
...

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/* The bootloader will look at this image and start execution at the symbol
   designated as the entry point. */
ENTRY(start)

/* Tell where the various sections of the object files will be put in the final
   kernel image. */
SECTIONS
{
    /* First put the multiboot header, as it is required to be put very early
       early in the image or the bootloader won't recognize the file format.
       Next we'll put the .text section. */
    .text BLOCK(4K) : ALIGN(4K)
    {
        *(.multiboot)
        *(.text)
    }

    /* Read-only data. */
    .rodata BLOCK(4K) : ALIGN(4K)
    {
        *(.rodata)
    }

    /* Read-write data (initialized) */
    .data BLOCK(4K) : ALIGN(4K)
    {
        *(.data)
    }

    /* Read-write data (uninitialized) and stack */
    .bss BLOCK(4K) : ALIGN(4K)
    {
        *(COMMON)
        *(.bss)
        *(.bootstrap_stack)
    }

    /* The compiler may produce other sections, by default it will put them in
       a segment with the same name. Simply add stuff here as needed. */
    .kend BLOCK(4K) : ALIGN(4K)
    {
        *(.kend)
    }
}

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 .text BLOCK(4K) : ALIGN(4K)
    {
        *(.multiboot)
        *(.text)
    }

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0x100000                add    0x31bad(%eax),%dh                    ; Start of Multiboot header      
0x100006                add    %al,(%eax)                          
0x100008                sti                                                
0x100009                dec    %edi                                        
0x10000a                push   %edx                                        
0x10000b                in     $0xbc,%al                           ; <------- this sets AL to 0xFF in QEMU.     
0x10000d <_start+1>     add    %dl,0x10(%eax)                              
0x100010 <_start+4>     add    %bh,%bl                                     
0x100012 <_start+6>     push   %eax                                        
0x100013 <_start+7>     push   %ebx                                        
0x100014 <_start+8>     call   0x100030 <kernel_main>