BarinkOS/source/kernel/boot/boot.s
Nigel 656ca0baa8 KERNEL: Pre-kernel sets up the physical memory manager.
* BUG: allocated blocks is possibly incorrect!
* prekernel no longer gets compiled as being in physical memory
2022-09-03 01:00:17 +02:00

114 lines
2.5 KiB
ArmAsm

.include "./source/kernel/boot/multiboot.s"
/*
* Allocate initial stack
*/
.section .bootstrap_stack, "aw", @nobits
stack_bottom:
.skip 16384 # 16 KiB
stack_top:
/*
* Preallocate a couple pages to get us bootstrapped
* Being carefull to not use any address the bootloader might
* be using for its multiboot structures
*/
.section .bss, "aw", @nobits
.align 4096
.globl boot_page_directory
boot_page_directory:
.skip 4096
.globl boot_page_table
boot_page_table:
.skip 4096
.globl multiboot_page_table
multiboot_page_table:
.skip 4096
# More page tables may be required
# Entry point
.section .multiboot.text, "a"
.globl _start
.type _start, @function
_start:
# Get physical address of the boot_page_table
movl $(boot_page_table - 0xC0000000), %edi
# Map address 0
movl $0, %esi
1:
cmpl $(_kernel_end - 0xC0000000), %esi
jge 3f
# Map physical address as "present and writable"
movl %esi, %edx
orl $0x003, %edx
movl %edx, (%edi)
2: # Size of page is 4096 bytes
addl $4096, %esi
# Size of entries in boot_page_table is 4 bytes
addl $4, %edi
# Loop to the next entry if we haven't finished.
loop 1b
3: # Map VGA video memory to 0xC03FF00 as "present, writable"
movl $(0x000B8000 | 0x003), boot_page_table - 0xC0000000 + 1023 * 4
# Map the page table to both virtual addresss 0x00000000 and 0xC0000000
movl $(boot_page_table - 0xC0000000 + 0x003), boot_page_directory - 0xC0000000 + 0
movl $(boot_page_table - 0xC0000000 + 0x003), boot_page_directory - 0xC0000000 + 768 * 4
# Set cr3 to the address of the boot_page_directory
movl $(boot_page_directory - 0xC0000000), %ecx
movl %ecx, %cr3
# Enable paging and the write-protect bit
movl %cr0, %ecx
orl $0x80010000, %ecx
movl %ecx, %cr0
# Jump to higher half with an absolute jump
lea 4f, %ecx
jmp *%ecx
.section .text
4:
# At this point, paging is fully set up and enabled
isPaging:
/* push the pointer to the Multiboot information structure*/
pushl %ebx
/* push the magic value */
pushl %eax
call prekernelSetup
# Unmap the identity mapping as it is now unnecessary
movl $0, boot_page_directory + 0
# Reload cr3 to force tlb flush
movl %cr3, %ecx
movl %ecx, %cr3
/*Setup the stack pointer to point to the beginning of our stack */
/* I believe its a high address growing down to lower adress for the stack on x86*/
mov $stack_top, %esp
/*Reset EFLAGS*/
pushl $0
popf
call early_main
cli
1: hlt
jmp 1b
.include "./source/kernel/memory/gdt/gdt.s"
.include "./source/kernel/irs_table.s"
.include "./source/kernel/irq_table.s"
.include "./source/kernel/interrupts/idt/idt.s"