feat: initial paging setup

boot/boot.S

@@ -19,7 +19,7 @@ forced to be within the first 8 KiB of the kernel file.
 .long CHECKSUM
 
 #.include "gdt.S"
-.section .data
+.section .boot.data, "aw", @progbits
 gdt:
 .quad 0x0000000000000000
 .quad 0x00CF9A000000FFFF
@@ -42,7 +42,7 @@ System V ABI standard and de-facto extensions. The compiler will assume the
 stack is properly aligned and failure to align the stack will result in
 undefined behavior.
 */
-.section .bss
+.section .boot.bss, "aw", @nobits
 .align 16
 stack_bottom:
 .skip 16384 # 16 KiB
@@ -53,7 +53,10 @@ 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
+.section .boot.text, "ax", @progbits
+
+.extern _boot_paging
+
 .global _start
 .type _start, @function
 _start:
@@ -77,6 +80,8 @@ _start:
 	*/
 	mov $stack_top, %esp
 
+	call _boot_paging
+
 	// store multiboot on stack
 	pushl 0
 	pushl %eax // MB code
@@ -101,6 +106,13 @@ _start:
     movw %ax,%gs
     ljmp $0x8, $continue_boot
 
+/*
+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
+
+.section .text
 continue_boot:
     sti
 	/*
@@ -129,9 +141,3 @@ continue_boot:
 	cli
 1:	#hlt
 	jmp 1b
-
-/*
-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

boot/bootpaging.S

@@ -0,0 +1,51 @@
+.code32
+.extern boot_paging_directory
+.extern boot_primary_table
+
+.section .boot.text, "ax", @progbits
+.global _boot_paging
+.type _boot_paging, @function
+_boot_paging:
+    push %ebp
+    mov %esp, %ebp
+    pusha
+    # Physical address of paging table 1
+    # movl $(boot_primary_table - 0xC0000000), %edi
+    movl $(boot_primary_table - 0xC0000000), %edi
+    movl $0, %esi
+    movl $1024, %ecx
+    cmpl %esi, %ecx
+_boot_paging_loop:
+    # stop when after kernel's last address
+    # cmpl $(_kernel_end -0xC0000000), %esi
+    cmpl $(_kernel_end), %esi
+    jge _boot_paging_after_kernel
+
+    # make address present and writable
+    movl %esi, %edx
+    orl $0x003, %edx
+    movl %edx, (%edi)
+
+    # next address
+    addl $4096, %esi
+    addl $4, %edi
+    loop _boot_paging_loop
+
+_boot_paging_after_kernel:
+    # write to directory
+    movl $(boot_primary_table - 0xC0000000 + 0x003), boot_paging_directory - 0xC0000000 + 0
+    movl $(boot_primary_table - 0xC0000000 + 0x003), boot_paging_directory - 0xC0000000 + 768 * 4
+
+    # write paging directory to cr3
+    movl $(boot_paging_directory - 0xC0000000), %ecx
+    movl %ecx, %cr3
+
+    # enable paging and write protect in cr0
+    movl %cr0, %ecx
+    orl $0x80010000, %ecx
+    movl %ecx, %cr0
+
+_boot_pagin_end:
+    popa
+    pop %ebp
+    ret