122 lines
3.0 KiB
ArmAsm
122 lines
3.0 KiB
ArmAsm
.include "./source/kernel/boot/multiboot.s"
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/*
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* Allocate initial stack
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*/
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.section .bootstrap_stack, "aw", @nobits
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stack_bottom:
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.skip 16384 # 16 KiB
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stack_top:
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/*
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* Preallocate a couple pages to get us bootstrapped
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* Being carefull to not use any address the bootloader might
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* be using for its multiboot structures
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*/
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.section .bss, "aw", @nobits
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.align 4096
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.globl boot_page_directory
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boot_page_directory:
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.skip 4096
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boot_page_table:
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.skip 4096
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.globl multiboot_page_table
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multiboot_page_table:
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.skip 4096
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# More page tables may be required
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# Entry point
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.section .multiboot.text, "a"
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.global _start
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.type _start, @function
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_start:
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/* push the pointer to the Multiboot information structure*/
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pushl %ebx
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/* push the magic value */
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pushl %eax
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call prekernelSetup
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# Get physical address of the boot_page_table
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movl $(boot_page_table - 0xC0000000), %edi
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# Map address 0
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movl $0, %esi
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1:
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cmpl $(_kernel_end - 0xC0000000), %esi
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jge 3f
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# Map physical address as "present and writable"
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movl %esi, %edx
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orl $0x003, %edx
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movl %edx, (%edi)
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2: # Size of page is 4096 bytes
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addl $4096, %esi
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# Size of entries in boot_page_table is 4 bytes
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addl $4, %edi
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# Loop to the next entry if we haven't finished.
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loop 1b
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3: # Map VGA video memory to 0xC03FF00 as "present, writable"
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movl $(0x000B8000 | 0x003), boot_page_table - 0xC0000000 + 1023 * 4
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# IMPORTANT NOTE FROM WIKI.OSDEV.ORG/HIGHER_HALF_X86_BARE_BONES
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# The page table is used at both page directory entry 0 (virtually from 0x0
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# to 0x3FFFFF) (thus identity mapping the kernel) and page directory entry
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# 768 (virtually from 0xC0000000 to 0xC03FFFFF) (thus mapping it in the
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# higher half). The kernel is identity mapped because enabling paging does
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# not change the next instruction, which continues to be physical. The CPU
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# would instead page fault if there was no identity mapping.\
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# Map the page table to both virtual addresss 0x00000000 and 0xC0000000
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movl $(boot_page_table - 0xC0000000 + 0x003), boot_page_directory - 0xC0000000 + 0
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movl $(boot_page_table - 0xC0000000 + 0x003), boot_page_directory - 0xC0000000 + 768 * 4
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# Set cr3 to the address of the boot_page_directory
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movl $(boot_page_directory - 0xC0000000), %ecx
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movl %ecx, %cr3
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# Enable paging and the write-protect bit
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movl %cr0, %ecx
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orl $0x80010000, %ecx
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movl %ecx, %cr0
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# Jump to higher half with an absolute jump
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lea 4f, %ecx
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jmp *%ecx
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.section .text
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4:
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# At this point, paging is fully set up and enabled
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isPaging:
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# Unmap the identity mapping as it is now unnecessary
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movl $0, boot_page_directory + 0
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# Reload cr3 to force tlb flush
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movl %cr3, %ecx
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movl %ecx, %cr3
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/*Setup the stack pointer to point to the beginning of our stack */
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/* I believe its a high address growing down to lower adress for the stack on x86*/
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mov $stack_top, %esp
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/*Reset EFLAGS*/
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pushl $0
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popf
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call early_main
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cli
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1: hlt
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jmp 1b
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.include "./source/kernel/Memory/GDT/gdt.s"
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.include "./source/kernel/irs_table.s"
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.include "./source/kernel/irq_table.s"
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.include "./source/kernel/Interrupts/idt/idt.s"
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.include "./source/kernel/cpu.s"
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