49 lines
1.9 KiB
ArmAsm
49 lines
1.9 KiB
ArmAsm
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//C main function for our kernel
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//See: kernel.c
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.extern kern_main
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//This will be our entrypoint function name - gotta initialize it now as global so the linker knows later.
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.global start
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//multiboot for GRUB to boot it. Ideally stage01_bootloader will be able to support the multiboot standard.
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//regardless of who's doing it, we have to set the required stuff
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.set MB_MAGIC, 0x1BADB002 // bytes that bootloader will use to find this place
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.set MB_FLAGS, (1 << 0) | (1 << 1) // flags request the following from the bootloader: maintain page boundaries + provide a memory map
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.set MB_CHECKSUM, (0 - (MB_MAGIC + MB_FLAGS)) // Fails if checksum doesn't pass. Kind of arbitrary, but required.
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//Now we actually place the multiboot stuff into the resulting executable...
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.section .multiboot
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.align 4 // 4 byte alignment
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.long MB_MAGIC
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.long MB_FLAGS
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.long MB_CHECKSUM
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// Set up for C code. Practically the only requirement for C-generated assembly to work properly is alignment and the presence of a stack.
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.section .bss
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.align 16
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stack_bottom:
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.skip 4096 // 4096 bytes (4kb) large stack. by skipping some amount of data (and eventually filling it with zeroes?), we've essentially just reserved space for our stack.
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//Remember, stack grows DOWNWARD! So the last thing in the section -> the highest memory address -> the very first thing on the stack!
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//Therefore, we put a label here to represent the top of our stack for later.
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stack_top:
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//Actual code. Entry point goes here!
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.section .text
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//Here it is!
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start:
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//Lets set up the stack. Stack grows downward on x86. We did the work earlier of defining where the top of the stack is, so just tell esp.
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mov $stack_top, %esp //set the stack pointer
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//To C-land!
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call kern_main
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//You should never get here, but in case you do, we will just hang.
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hang:
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cli //Interrupts: off
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hlt //Halt!
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jmp hang //just in case...
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