60 lines
1.6 KiB
ArmAsm
60 lines
1.6 KiB
ArmAsm
## Bare bone boot.s from wiki.osdev.org
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# multiboot header
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.section .rodata.multiboot
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.align 4
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# magic number
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.long 0x1BADB002
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# flags: align, meminfo
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.long 0x3
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# checksum: -(magic+flags)
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.long -(0x1BADB002 + 0x3)
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# the initial kernel stack
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.section .kernel_stack
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.global os_stack
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.size os_stack, 4096
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#.Lstack_bottom:
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os_stack:
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.byte 0
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#.skip 16384 # 16 KiB
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.skip 4094 # 4 KiB
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.byte 0
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.Lstack_top:
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# The linker script specifies _start as the entry point to the kernel and the
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# bootloader will jump to this position once the kernel has been loaded. It
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# doesn't make sense to return from this function as the bootloader is gone.
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.section .text.startup
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.global _start
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.type _start, @function
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_start:
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# Welcome to kernel mode!
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# To set up a stack, we simply set the esp register to point to the top of
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# our stack (as it grows downwards).
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movl $.Lstack_top, %esp
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# We are now ready to actually execute C code. (see ./startup.cc)
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call os_main
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# In case the function returns, we'll want to put the computer into an
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# infinite loop. To do that, we use the clear interrupt ('cli') instruction
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# to disable interrupts, the halt instruction ('hlt') to stop the CPU until
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# the next interrupt arrives, and jumping to the halt instruction if it ever
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# continues execution, just to be safe. We will create a local label rather
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# than real symbol and jump to there endlessly.
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cli
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hlt
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.Lhang:
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jmp .Lhang
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# Set the size of the _start symbol to the current location '.' minus its start.
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# This is useful when debugging or when you implement call tracing.
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.size _start, . - _start
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