Delete boot.s

minimalOS/boot.s

-# Declare constants used for creating a multiboot header.
-.set ALIGN,    1<<0             # align loaded modules on page boundaries
-.set MEMINFO,  1<<1             # provide memory map
-.set FLAGS,    ALIGN | MEMINFO  # this is the Multiboot 'flag' field
-.set MAGIC,    0x1BADB002       # 'magic number' lets bootloader find the header
-.set CHECKSUM, -(MAGIC + FLAGS) # checksum of above, to prove we are multiboot
-
-# Declare a header as in the Multiboot Standard. We put this into a special
-# section so we can force the header to be in the start of the final program.
-# You don't need to understand all these details as it is just magic values that
-# is documented in the multiboot standard. The bootloader will search for this
-# magic sequence and recognize us as a multiboot kernel.
-.section .multiboot
-.align 4
-.long MAGIC
-.long FLAGS
-.long CHECKSUM
-
-# Currently the stack pointer register (esp) points at anything and using it may
-# cause massive harm. Instead, we'll provide our own stack. We will allocate
-# room for a small temporary stack by creating a symbol at the bottom of it,
-# then allocating 16384 bytes for it, and finally creating a symbol at the top.
-.section .bootstrap_stack, "aw", @nobits
-stack_bottom:
-.skip 16384 # 16 KiB
-stack_top:
-
-# The linker script specifies _start as the entry point to the kernel and the
-# bootloader will jump to this position once the kernel has been loaded. It
-# doesn't make sense to return from this function as the bootloader is gone.
-.section .text
-.global _start
-.type _start, @function
-_start:
-	# Welcome to kernel mode! We now have sufficient code for the bootloader to
-	# load and run our operating system. It doesn't do anything interesting yet.
-	# Perhaps we would like to call printf("Hello, World\n"). You should now
-	# realize one of the profound truths about kernel mode: There is nothing
-	# there unless you provide it yourself. There is no printf function. There
-	# is no <stdio.h> header. If you want a function, you will have to code it
-	# yourself. And that is one of the best things about kernel development:
-	# you get to make the entire system yourself. You have absolute and complete
-	# power over the machine, there are no security restrictions, no safe
-	# guards, no debugging mechanisms, there is nothing but what you build.
-
-	# By now, you are perhaps tired of assembly language. You realize some
-	# things simply cannot be done in C, such as making the multiboot header in
-	# the right section and setting up the stack. However, you would like to
-	# write the operating system in a higher level language, such as C or C++.
-	# To that end, the next task is preparing the processor for execution of
-	# such code. C doesn't expect much at this point and we only need to set up
-	# a stack. Note that the processor is not fully initialized yet and stuff
-	# such as floating point instructions are not available yet.
-
-	# To set up a stack, we simply set the esp register to point to the top of
-	# our stack (as it grows downwards).
-	movl $stack_top, %esp
-
-	# We are now ready to actually execute C code. We cannot embed that in an
-	# assembly file, so we'll create a kernel.c file in a moment. In that file,
-	# we'll create a C entry point called kernel_main and call it here.
-	call kernel_main
-
-	# In case the function returns, we'll want to put the computer into an
-	# infinite loop. To do that, we use the clear interrupt ('cli') instruction
-	# to disable interrupts, the halt instruction ('hlt') to stop the CPU until
-	# the next interrupt arrives, and jumping to the halt instruction if it ever
-	# continues execution, just to be safe. We will create a local label rather
-	# than real symbol and jump to there endlessly. 
-	cli
-	hlt
-.Lhang:
-	jmp .Lhang
-
-# Set the size of the _start symbol to the current location '.' minus its start.
-# This is useful when debugging or when you implement call tracing.
-.size _start, . - _start