1 files changed, 138 insertions, 0 deletions
diff --git a/kernel/boot.S b/kernel/boot.S
new file mode 100644
index 0000000..4276c98
--- /dev/null
+++ b/kernel/boot.S
@@ -0,0 +1,138 @@
+.global _start
+.extern begin_long_mode
+
+.section .text
+.code32
+
+_start:
+	mov $stack_top, %esp
+
+	call check_multiboot
+	call check_cpuid
+	call check_long_mode
+
+	call setup_page_tables
+	call enable_paging
+
+	lgdt gdt64_pointer
+	ljmp $gdt64_code_segment, $begin_long_mode
+
+
+check_multiboot:
+	cmp $0x36d76289, %eax
+	jne no_multiboot
+
+	ret
+
+check_cpuid:
+	pushfl
+	pop %eax
+	mov %eax, %ecx
+	xor $1<<21, %eax
+	push %eax
+	popfl
+	pushfl
+	pop %eax
+	push %ecx
+	popfl
+	cmp %eax, %ecx
+	je no_cpuid
+
+	ret
+
+check_long_mode:
+	mov $0x80000000, %eax
+	cpuid
+	cmp $0x80000001, %eax
+	jb no_long_mode
+
+	mov $0x80000001, %eax
+	cpuid
+	test $1<<29, %edx
+	jz no_long_mode
+
+	ret
+
+setup_page_tables:
+	mov $page_table_lvl3, %eax
+	or $0x3, %eax
+	mov %eax, page_table_lvl4
+
+	mov $page_table_lvl2, %eax
+	or $0x3, %eax
+	mov %eax, page_table_lvl3
+
+	movl $0, %ecx
+1:
+	movl $0x200000, %eax
+	mul %ecx
+	or $0b10000011, %eax
+	movl $page_table_lvl2, %edx
+	leal (%edx, %ecx, 8), %edx
+	movl %eax, (%edx)
+	inc %ecx
+	cmp $512, %ecx
+	jne 1b
+
+	ret
+
+enable_paging:
+	// enable PAE
+	mov %cr4, %edx
+	or $1<<5 ,%edx
+	mov %edx, %cr4
+
+	// set LME (long mode enable)
+	mov $0xC0000080, %ecx
+	rdmsr
+	or $1<<8, %eax
+	wrmsr
+
+	// page_table_lvl4
+	mov $page_table_lvl4, %eax
+	mov %eax, %cr3
+
+	// enable paging (+ protected mode if not already enabled)
+	mov %cr0, %eax
+	or $1<<31 + 1<<0, %eax
+	mov %eax, %cr0
+
+	ret
+
+no_multiboot:
+	movl $0x4f4d, 0xb8000
+	hlt
+
+no_cpuid:
+	movl $0x4f43, 0xb8000
+	hlt
+
+no_long_mode:
+	movl $0x4f4c, 0xb8000
+	hlt
+
+
+.section .bss
+.align 4096
+
+// stack
+stack_bottom:
+	.skip 4096*4
+stack_top:
+
+// page tables
+page_table_lvl4:
+	.skip 4096
+page_table_lvl3:
+	.skip 4096
+page_table_lvl2:
+	.skip 4096
+
+.section .rodata
+gdt64:
+	.quad 0
+gdt64_code_segment = . - gdt64
+	.quad 1<<43 + 1<<44 + 1<<47 + 1<<53
+gdt64_pointer:
+	.word . - gdt64 - 1
+	.quad gdt64