1 files changed, 86 insertions, 0 deletions
diff --git a/src/kernel/core/loader.s b/src/kernel/core/loader.s
new file mode 100644
index 0000000..447d82d
--- /dev/null
+++ b/src/kernel/core/loader.s
@@ -0,0 +1,86 @@
+[EXTERN kmain]            ; kmain is defined in kmain.c
+[GLOBAL loader]           ; making entry point visible to linker
+[GLOBAL kernel_pd]   	  ; make kernel page directory visible
+[GLOBAL kernel_stack_protector] 		; used to detect kernel stack overflow
+[GLOBAL kernel_stack_top] 				; stack re-used by scheduler
+
+; higher-half kernel setup
+K_HIGHHALF_ADDR     equ 0xC0000000
+K_PAGE_NUMBER       equ (K_HIGHHALF_ADDR >> 22)
+
+; loader stack size
+LOADER_STACK_SIZE   equ 0x8000		; 8Kb
+
+; setting up the Multiboot header - see GRUB docs for details
+MODULEALIGN         equ 1<<0                   ; align loaded modules on page boundaries
+MEMINFO             equ 1<<1                   ; provide memory map
+FLAGS               equ MODULEALIGN | MEMINFO  ; this is the Multiboot 'flag' field
+MAGIC               equ 0x1BADB002           ; 'magic number' lets bootloader find the header
+CHECKSUM            equ -(MAGIC + FLAGS)        ; checksum required
+
+[section .setup]
+align 4
+multiboot_header:
+	dd MAGIC
+	dd FLAGS
+	dd CHECKSUM
+
+loader:	
+	; setup the boot page directory used for higher-half
+	mov ecx, kernel_pd
+	sub ecx, K_HIGHHALF_ADDR	; access its lower-half address
+	mov cr3, ecx
+
+	; Set PSE bit in CR4 to enable 4MB pages.
+	mov ecx, cr4
+	or ecx, 0x00000010
+	mov cr4, ecx
+
+	; Set PG bit in CR0 to enable paging.
+	mov ecx, cr0
+	or ecx, 0x80000000
+	mov cr0, ecx
+
+	; long jump required
+	lea ecx, [higherhalf]
+	jmp ecx
+
+[section .data]
+align 0x1000
+kernel_pd:
+	; uses 4MB pages
+	; identity-maps the first 4Mb of RAM, and also maps them with offset += k_highhalf_addr
+	dd 0x00000083
+	times (K_PAGE_NUMBER - 1) dd 0
+	dd 0x00000083
+	times (1024 - K_PAGE_NUMBER - 1) dd 0
+
+[section .text]
+higherhalf:		; now we're running in higher half
+	; unmap first 4Mb
+	mov dword [kernel_pd], 0
+	invlpg [0]
+
+	mov esp, kernel_stack_top   ; set up the stack
+
+	push eax                    ; pass Multiboot magic number
+	add ebx, K_HIGHHALF_ADDR    ; update the MB info structure so that it is in higher half
+	push ebx                    ; pass Multiboot info structure
+
+	call  kmain                 ; call kernel proper
+
+hang:
+	; halt machine should kernel return
+	cli
+	hlt
+	jmp   hang
+
+[section .bss]
+align 0x1000
+kernel_stack_protector:
+	resb 0x1000			; as soon as we have efficient paging, we WON'T map this page
+kernel_stack_bottom:
+	resb LOADER_STACK_SIZE
+kernel_stack_top:
+
+; vim: set ts=4 sw=4 tw=0 noet :