banan-os/kernel/arch/i386/boot.S

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# Declare constants for the multiboot header
.set ALIGN, 1<<0 # align loaded modules on page boundaries
.set MEMINFO, 1<<1 # provide memory map
.set VIDEOINFO, 1<<2 # provide video info
.set MB_FLAGS, ALIGN | MEMINFO | VIDEOINFO # this is the Multiboot 'flag' field
.set MB_MAGIC, 0x1BADB002 # 'magic number' lets bootloader find the header
.set MB_CHECKSUM, -(MB_MAGIC + MB_FLAGS) #checksum of above, to prove we are multiboot
# Multiboot header
.section .multiboot, "aw"
.align 4
.long MB_MAGIC
.long MB_FLAGS
.long MB_CHECKSUM
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.skip 20
.long 0
.long 800
.long 600
.long 32
.section .bss, "aw", @nobits
# Create stack
stack_bottom:
.skip 16384
stack_top:
.global g_kernel_cmdline
g_kernel_cmdline:
.skip 4096
# Reserve memory for paging structures,
# we will identity map first 4 MiB
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# 0 MiB -> 1 MiB: bootloader stuff
# 1 MiB -> 2 MiB: kernel
# 2 MiB -> 3 MiB: kmalloc
# 3 MiB -> 4 Mib: kmalloc_eternal
.align 32
boot_page_directory_pointer_table:
.skip 4 * 8
.align 4096
boot_page_directory1:
.skip 512 * 8
.section .text, "a"
.global g_multiboot_info
g_multiboot_info:
.skip 4
.global g_multiboot_magic
g_multiboot_magic:
.skip 4
has_cpuid:
pushfl
pushfl
xorl $0x00200000, (%esp)
popfl
pushfl
popl %eax
xorl (%esp), %eax
popfl
andl $0x00200000, %eax
ret
has_pae:
call has_cpuid
cmpl $0, %eax
jz .exit
movl $0, %eax
cpuid
movl %edx, %eax
andl $0x40, %eax # PAE is bit 6 in edx
.exit:
ret
.global _start
.type _start, @function
_start:
# Initialize stack and multiboot info
movl $stack_top, %esp
movl %eax, g_multiboot_magic
movl %ebx, g_multiboot_info
# Copy kernel command line to known location
movl %ebx, %esi
addl $16, %esi
movl (%esi), %esi
movl $1024, %ecx
movl $g_kernel_cmdline, %edi
rep movsl
call has_pae
cmpl $0, %eax
jz system_halt
# identity map first 4 MiB
movl $(0x00000000 + 0x83), boot_page_directory1 + 0
movl $(0x00200000 + 0x83), boot_page_directory1 + 8
movl $(boot_page_directory1 + 0x01), boot_page_directory_pointer_table
# enable PAE
movl %cr4, %ecx
orl $0x20, %ecx
movl %ecx, %cr4
# set address of paging structures
movl $boot_page_directory_pointer_table, %ecx
movl %ecx, %cr3
# enable paging
movl %cr0, %ecx
orl $0x80000000, %ecx
movl %ecx, %cr0
# call global constuctors
call _init
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# call to the kernel itself (clear ebp for stacktrace)
xorl %ebp, %ebp
call kernel_main
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# call global destructors
call _fini
system_halt:
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xchgw %bx, %bx
cli
1: hlt
jmp 1b