loader.S

# loader.s

.global loader           # making entry point visible to linker

# setting up the Multiboot header - see GRUB docs for details
.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 required

.align 4
.long MAGIC
.long FLAGS
.long CHECKSUM

# reserve initial kernel stack space
.set STACKSIZE, 0x4000          # that's 16k.
.comm stack, STACKSIZE, 32      # reserve 16k stack on a quadword boundary

loader:       mov   $(stack + STACKSIZE), %esp # set up the stack
              push  %eax                       # Multiboot magic number
              push  %ebx                       # Multiboot data structure

              call  main            # call kernel proper
              hlt                    # halt machine should kernel return