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.set ALIGN, 1<<0
.set MEMINFO, 1<<1
.set VIDEO_MODE, 1<<2
.set FLAGS, VIDEO_MODE|ALIGN | MEMINFO
.set MAGIC, 0x1BADB002
.set CHECKSUM, -(MAGIC + FLAGS)
#.section .multiboot
.align 16, 0
.section .multiboot.data, "aw"
.align 4
.long MAGIC
.long FLAGS
.long CHECKSUM
# unused(padding)
.long 0,0,0,0,0
# Video mode
.long 0 # Linear graphics
.long 0 # Preferred width
.long 0 # Preferred height
.long 32 # Preferred pixel depth
# Allocate the initial stack.
.section .bootstrap_stack, "aw", @nobits
stack_bottom:
.skip 16384 # 16 KiB
stack_top:
.global boot_page_directory
.global boot_page_table1
.section .bss, "aw", @nobits
.align 4096
boot_page_directory:
.skip 4096
boot_page_table1:
.skip 4096
heap_table:
.skip 4096
.section .multiboot.text, "a"
.global _start
.extern _kernel_end
.type _start, @function
# Kernel entry
_start:
# edi contains the buffer we wish to modify
movl $(boot_page_table1 - 0xC0000000), %edi
# for loop
movl $0, %esi
movl $1024, %ecx
1:
# esi = address
# If we are in kernel range jump to "label 2"
cmpl $_kernel_start, %esi
jl 2f
# If we are past the kernel jump to the final stage
# "label 3"
cmpl $(_kernel_end- 0xC0000000), %esi
jge heap_start
2:
# Add permission to the pages
movl %esi, %edx
orl $0x003, %edx
movl %edx, (%edi)
# Size of page is 4096 bytes.
addl $4096, %esi
# Size of entries in boot_page_table1 is 4 bytes.
addl $4, %edi
# Loop to the next entry if we haven't finished.
loop 1b
heap_start:
# edi contains the buffer we wish to modify
movl $(heap_table - 0xC0000000), %edi
# for loop
movl $1024, %ecx
addl $4096, %esi
heap:
movl %esi, %edx
orl $0x003, %edx
movl %edx, (%edi)
# Size of page is 4096 bytes.
addl $4096, %esi
# Size of entries is 4 bytes.
addl $4, %edi
loop heap
final:
# Map the page table to both virtual addresses 0x00000000 and 0xC0000000.
movl $(boot_page_table1 - 0xC0000000 + 0x003), boot_page_directory - 0xC0000000 + 0
movl $(boot_page_table1 - 0xC0000000 + 0x003), boot_page_directory - 0xC0000000 + 768 * 4
movl $(heap_table - 0xC0000000 + 0x003), boot_page_directory - 0xC0000000 + 769 * 4
# Set cr3 to the address of the boot_page_directory.
movl $(boot_page_directory - 0xC0000000), %ecx
movl %ecx, %cr3
# Enable paging
movl %cr0, %ecx
orl $0x80000000, %ecx
movl %ecx, %cr0
# Jump to higher half with an absolute jump.
lea 4f, %ecx
jmp *%ecx
.size _start, . - _start
.section .text
4:
# At this point, paging is fully set up and enabled.
# Unmap the identity mapping as it is now unnecessary.
movl $0, boot_page_directory + 0
# Reload crc3 to force a TLB flush so the changes to take effect.
movl %cr3, %ecx
movl %ecx, %cr3
# Set up the stack.
mov $stack_top, %esp
# Reset EFLAGS.
pushl $0
popf
pushl %esp
/* Push the pointer to the Multiboot information structure. */
pushl %ebx
/* Push the magic value. */
pushl %eax
mov $_kernel_end, %eax
pushl %eax
# Enter the high-level kernel.
call kernel_main
# Infinite loop if the system has nothing more to do.
cli
1: hlt
jmp 1b
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