140 lines
4.0 KiB
ArmAsm
140 lines
4.0 KiB
ArmAsm
/*
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* Copyright (C) 2018 Ortega Froysa, Nicolás <nortega@themusicinnoise.net>
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* Author: Ortega Froysa, Nicolás <nortega@themusicinnoise.net>
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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# declare constants for the multiboot header
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.set ALIGN, 1 << 0 # align loaded modules on page boundaries
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.set MEMINFO, 1 << 1 # provide memory map
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.set FLAGS, ALIGN | MEMINFO # the multiboot `FLAG' field
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.set MAGIC, 0x1BADB002 # 'magic number' letting the boot loader know we're here
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.set CHECKSUM , -(MAGIC + FLAGS) # checksum of the above to prove we're multiboot
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/*
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* Declare the multiboot header marking this program as a kernel. The bootloader
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* will search for these values in the first 8 KiB of the kernel file aligned at
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* 32-bit boundaries (4 bytes). We put the signature in its own section to force
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* it within the first 8 KiB of the kernel file.
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*/
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.section .multiboot
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.align 4
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.long MAGIC
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.long FLAGS
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.long CHECKSUM
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/*
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* Create a 16 byte aligned stack with 16 KiB of size. We create labels at the
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* bottom and top of the stack.
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*/
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.section .bss
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.align 16
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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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* Create the GDT
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*/
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.section .data
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gdt_start:
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gdt_null:
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.long 0x0
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.long 0x0
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gdt_kcode:
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.word 0xFFFF # limit
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.word 0x0 # base
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.byte 0x0 # base
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.byte 0b10011010 # 1st flags | type flags
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.byte 0b11001111 # 2nd flags | limit
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.byte 0x0 # base
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gdt_kdata:
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.word 0xFFFF # limit
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.word 0x0 # base
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.byte 0x0 # base
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.byte 0b10010010 # 1st flags | type flags
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.byte 0b11001111 # 2nd flags | limit
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.byte 0x0 # base
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gdt_ucode:
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.word 0xFFFF # limit
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.word 0x0 # base
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.byte 0x0 # base
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.byte 0b11111010 # 1st flags | type flags
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.byte 0b11001111 # 2nd flags | limit
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.byte 0x0 # base
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gdt_udata:
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.word 0xFFFF # limit
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.word 0x0 # base
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.byte 0x0 # base
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.byte 0b11110010 # 1st flags | type flags
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.byte 0b11001111 # 2nd flags | limit
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.byte 0x0 # base
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# TODO: setup the TSS
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gdt_tss:
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.word 0x0 # size of TSS (set later)
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.word 0x0 # address of TSS (set later)
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.byte 0x0 # address of TSS (set later)
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.byte 0b10010001 # 1st flags | type flags
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.byte 0b01000000 # 2nd flags | size of TSS (set later
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.byte 0x0 # address of TSS (set later)
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gdt_end:
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gdtr:
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.word (gdt_end - gdt_start - 1)
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.long gdt_start
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/*
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* The linker script specifies the `_start' label as the entry point to the kernel
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* and the bootloader will jump to this position. That is, this is where the kernel
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* starts.
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*/
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.section .text
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.global _start
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.type _start, @function
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_start:
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# set the position of `%esp' to the top of the stack
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mov $stack_top, %esp
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# GDT, paging, and other features
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flush_gdt:
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cli
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lgdt (gdtr)
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movw $0x10, %ax
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movw %ax, %ds
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movw %ax, %es
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movw %ax, %fs
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movw %ax, %gs
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movw %ax, %ss
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ljmp $0x08, $flush_end
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flush_end:
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boot_kernel:
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# enter high-level kernel (C)
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call kernel_main
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# put computer into infinite loop
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cli # disable interrupts by clearing the interrupt flag in `eflags'
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end_loop:
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hlt # wait for next interrupt
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jmp end_loop # jump to the `hlt' instruction if it ever leaves it
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.size _start, . - _start
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