2020-12-02 02:41:09 +00:00
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# Constants for multiboot
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.set ALIGN, 1<<0 # align on page boundaries
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.set MEMINFO, 1<<1 # memory map
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.set FLAGS, ALIGN | MEMINFO # for multiboot 'flag' field
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.set MAGIC, 0x1BADB002 # magic number for bootloader
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.set CHECKSUM, -(MAGIC + FLAGS) # checksum to prove we're multiboot
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# Declare header for multiboot
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2022-10-29 15:03:56 +00:00
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.section .multiboot.data, "aw"
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2020-12-02 02:41:09 +00:00
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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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# Reserve stack for initial thread
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2022-10-29 15:03:56 +00:00
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.section .bootstrap_stack, "aw", @nobits
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2020-12-02 02:41:09 +00:00
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stack_bottom:
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.skip 16384 # 16K
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stack_top:
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2022-10-29 15:03:56 +00:00
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# Preallocate pages for paging
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.section .bss, "aw", @nobits
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.align 4096
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boot_page_directory:
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.skip 4096
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boot_page_table1:
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.skip 4096
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# May need additional page for kernel > 3 MiB
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2020-12-02 02:41:09 +00:00
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# Kernel entry
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2022-10-29 15:03:56 +00:00
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.section .multiboot.text, "a"
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2020-12-02 02:41:09 +00:00
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.global _start
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.type _start, @function
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_start:
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2022-10-29 15:03:56 +00:00
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# Physical address of boot_page_table 1
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movl $(boot_page_table1 - 0xC0000000), %edi
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# Map address 0
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movl $0, %esi
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# Map first 1023 pages
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movl $1023, %ecx
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1:
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# Only map the kernel
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cmpl $_kernel_start, %esi
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jl 2f
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cmpl $(_kernel_end - 0xC0000000), %esi
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jge 3f
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# Map physical address as "present, writable"
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# TODO: map .text and .rodata as non-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:
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# Size of page is 4KiB
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addl $4096, %esi
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# Size of entries in boot_page_table1 is 4 bytes
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addl $4, %edi
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# Loop to next if not done
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loop 1b
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3:
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# Map VGA memory to 0xC03FF000 as "present, writable"
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movl $(0x000B8000 | 0x003), boot_page_table1 - 0xC0000000 + 1023 * 4
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# Map page table to 0x0 and 0xC0000000
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movl $(boot_page_table1 - 0xC0000000 + 0x003), boot_page_directory - 0xC0000000 + 0
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movl $(boot_page_table1 - 0xC0000000 + 0x003), boot_page_directory - 0xC0000000 + 768 * 4
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# Set cr3 to address of 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 write-protect
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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
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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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# Unmap identity mapping
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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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# Set up stack
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mov $stack_top, %esp
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2020-12-02 02:41:09 +00:00
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# Call global constructors
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call _init
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# Start kernel
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call kern_main
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# Hang if kernel returns
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cli
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1: hlt
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jmp 1b
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