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sortix--sortix/kernel/x64/boot.S
2014-03-01 14:37:40 +01:00

197 lines
5.1 KiB
ArmAsm

/*******************************************************************************
Copyright(C) Jonas 'Sortie' Termansen 2011.
This file is part of Sortix.
Sortix is free software: you can redistribute it and/or modify it under the
terms of the GNU General Public License as published by the Free Software
Foundation, either version 3 of the License, or (at your option) any later
version.
Sortix is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
details.
You should have received a copy of the GNU General Public License along with
Sortix. If not, see <http://www.gnu.org/licenses/>.
x64/boot.S
Bootstraps the kernel and passes over control from the boot-loader to the
kernel main function. It also jumps into long mode!
*******************************************************************************/
.section .text
.text 0x100000
.global _start
.type _start, @function
.code32
_start:
jmp prepare_kernel_execution
# Align 32 bits boundary.
.align 4
# Multiboot header.
multiboot_header:
# Magic.
.long 0x1BADB002
# Flags.
.long 0x00000003
# Checksum.
.long -(0x1BADB002 + 0x00000003)
prepare_kernel_execution:
# We got our multiboot information in various registers. But we are going
# to need these registers. But where can we store them then? Oh hey, let's
# store then in the code already run!
# Store the pointer to the Multiboot information structure.
mov %ebx, 0x100000
# Store the magic value.
mov %eax, 0x100004
# Clear the first $0xE000 bytes following 0x21000.
movl $0x21000, %edi
mov %edi, %cr3
xorl %eax, %eax
movl $0xE000, %ecx
rep stosl
movl %cr3, %edi
# Set the initial page tables.
# Note that we OR with 0x7 here to allow user-space access, except in the
# first 2 MiB. We also do this with 0x200 to allow forking the page.
# Page-Map Level 4
movl $0x22207, (%edi)
addl $0x1000, %edi
# Page-Directory Pointer Table
movl $0x23207, (%edi)
addl $0x1000, %edi
# Page-Directory (no user-space access here)
movl $0x24003, (%edi) # (First 2 MiB)
movl $0x25003, 8(%edi) # (Second 2 MiB)
addl $0x1000, %edi
# Page-Table
# Memory map the first 4 MiB.
movl $0x3, %ebx
movl $1024, %ecx
SetEntry:
mov %ebx, (%edi)
add $0x1000, %ebx
add $8, %edi
loop SetEntry
# Enable PAE.
mov %cr4, %eax
orl $0x20, %eax
mov %eax, %cr4
# Enable long mode.
mov $0xC0000080, %ecx
rdmsr
orl $0x100, %eax
wrmsr
# Enable paging and enter long mode (still 32-bit)
mov %cr0, %eax
orl $0x80000000, %eax
mov %eax, %cr0
# Load the long mode GDT.
mov GDTPointer, %eax
lgdtl GDTPointer
# Now use the 64-bit code segment, and we are in full 64-bit mode.
ljmp $0x10, $Realm64
.code64
Realm64:
# Now, set up the other segment registers.
cli
mov $0x18, %ax
mov %ax, %ds
mov %ax, %es
mov %ax, %fs
mov %ax, %gs
# Enable the floating point unit.
mov %cr0, %rax
and $0xFFFD, %ax
or $0x10, %ax
mov %rax, %cr0
fninit
# Enable Streaming SIMD Extensions.
mov %cr0, %rax
and $0xFFFB, %ax
or $0x2, %ax
mov %rax, %cr0
mov %cr4, %rax
or $0x600, %rax
mov %rax, %cr4
# Alright, that was the bootstrap code. Now begin preparing to run the
# actual 64-bit kernel.
jmp Main
.size _start, . - _start
.section .data
GDT64: # Global Descriptor Table (64-bit).
GDTNull: # The null descriptor.
.word 0 # Limit (low).
.word 0 # Base (low).
.byte 0 # Base (middle)
.byte 0 # Access.
.byte 0 # Granularity.
.byte 0 # Base (high).
GDTUnused: # The null descriptor.
.word 0 # Limit (low).
.word 0 # Base (low).
.byte 0 # Base (middle)
.byte 0 # Access.
.byte 0 # Granularity.
.byte 0 # Base (high).
GDTCode: # The code descriptor.
.word 0xFFFF # Limit (low).
.word 0 # Base (low).
.byte 0 # Base (middle)
.byte 0x9A # Access.
.byte 0xAF # Granularity.
.byte 0 # Base (high).
GDTData: # The data descriptor.
.word 0xFFFF # Limit (low).
.word 0 # Base (low).
.byte 0 # Base (middle)
.byte 0x92 # Access.
.byte 0x8F # Granularity.
.byte 0 # Base (high).
GDTPointer: # The GDT-pointer.
.word GDTPointer - GDT64 - 1 # Limit.
.long GDT64 # Base.
.long 0
Main:
# Copy the character B onto the screen so we know it works.
movq $0x242, %r15
movq %r15, %rax
movw %ax, 0xB8000
# Load the pointer to the Multiboot information structure.
mov 0x100000, %ebx
# Load the magic value.
mov 0x100004, %eax
jmp beginkernel
.size Main, . - Main