Finished implementing paging init and long mode switch

arch/x86_64/start_32.S

@@ -6,6 +6,8 @@
 .set CHECKSUM,	   -(MAGIC + FLAGS)
 
 /* the amount of memory to allocate for bootstrap page directories. */
+/* with buffer size 0x1000 (enough for exactly one page directory)
+/* we can map 1 GiB of virtual memory */
 #define BOOTSTRAP_PDIR_SIZE 0x1000
 
 .extern start_64	# defined in start_64.S
@@ -13,12 +15,41 @@
 .code32
 
 .section .boot.rodata, "a", @progbits
+
+/*******
+  ERROR MESSAGE STRINGS
+ *******/
 no_long_mode_err:
     .asciz "This system is not 64-bit. Press any key to reboot."
 
 unsupported_cpu_err:
     .asciz "Your CPU is not supported by Magenta. Press any key to reboot."
 
+
+/*******
+  LONG MDOE BOOSTRAP GDT
+ *******/
+bootstrap_gdt:
+	/* 0x00: null descriptor */
+	.long 0x0
+	.long 0x0
+
+	/* 0x08: kernel code segment */
+	.long 0x0000ffff
+	.long 0x002f9a00
+
+	/* 0x10: kernel data segment */
+	.long 0x0000ffff
+	.long 0x002f9200
+
+bootstrap_gdt_ptr:
+	.word 24 /* 8 bytes for each entry in bootstrap_gdt */
+	.long bootstrap_gdt
+
+
+/*******
+  LONG MODE BOOTSTRAP PAGING STRUCTURES
+ *******/
 .section .boot.bss, "aw", @nobits
 bootstrap_pml4t:		# a single PML4T
 	.skip 0x1000
@@ -30,6 +61,9 @@ bootstrap_stack_bottom:
 	.skip 0x1000
 bootstrap_stack_top:
 
+/*******
+  MULTIBOOT HEADER
+ *******/
 .section .boot.text, "ax", @progbits
 .align 4
 .long MAGIC
@@ -94,6 +128,8 @@ unsupported_cpu:
 	cli
 	hlt
 
+.global init_page_tables
+.type init_page_tables, @function
 init_page_tables:
 	/* STEP 1: add an entry in the PML4T pointing to the PDPT.
 	   NOTE that we actually add two entries in the PML4T that both point to the same PDPT.
@@ -103,7 +139,7 @@ init_page_tables:
 	mov $bootstrap_pdpt, %esi
 
 	# in %ESI, build a PML4T entry containing the base address of the PDPT
-	xor $0xFFF, %esi
+	and $0xFFFFF000, %esi
 	or $0x3, %esi
 
 	# add the PML4T entries at PML4T[0] and PML4T[511]
@@ -111,8 +147,7 @@ init_page_tables:
 	add $0xFF8, %edi
 	mov %esi, (%edi)
 
-	/* STEP 2: initialise the PDPT.
-	   We need to create an entry in the PDPT for every page directory we intend to use. */
+	/* STEP 2: write the pgdir entries to the BEGINNING of the PDPT */
 
 	# BOOTSTRAP_PDIR_SIZE contains the total size of the page directory buffer.
 	# use it to calculate the number of page directories we're using.
@@ -129,22 +164,61 @@ init_page_tables:
 	   %EBX is where we build the PDPT entry. */
 1:
 	mov %esi, %ebx
-	xor $0xFFF, %ebx
+	and $0xFFFFF000, %ebx
 	or $0x3, %ebx
 
-	# skip the first 4 bytes of the 8-byte entry, leaving them zero.
-	add $0x4, %edi
 	mov %ebx, (%edi)
 
 	add $0x1000, %esi
-	add $0x4, %edi
+	add $0x8, %edi
 	sub $0x1, %eax
 
 	cmp $0x0, %eax
 	jne 1b
 
-	/* STEP 3: initialise the page directories.
-	   Each page directory can be used to map 2MiB of virtual memory.
+	/* STEP 3: write the pgdir entries to the END of the PDPT */
+
+	# BOOTSTRAP_PDIR_SIZE contains the total size of the page directory buffer.
+	# use it to calculate the number of page directories we're using.
+	mov $0, %edx
+	mov $BOOTSTRAP_PDIR_SIZE, %eax
+	mov $0x1000, %ebx
+	idiv %ebx
+
+	mov $bootstrap_pdpt, %edi
+	mov $bootstrap_pdir_buf, %esi
+
+	/* with the number of page directories in %EAX, calculate the starting index into the PDPT.
+	   we need to duplicate the pgdir entries here to map the kernel at vaddr 0xffffffff80000000 and up */
+	mov %eax, %ecx
+	mov $0x8, %edx
+	mul %edx
+	xchg %eax, %ecx
+	add $0x1000, %edi
+	sub %ecx, %edi
+	sub $0x08, %edi			# subtract one from the index here, otherwise the mapping will be at 0xffffffffc0000000
+							# (each entry in the array is 8 bytes long)
+
+	/* %ESI is a pointer into the pagedir buffer.
+	   %EDI is a pointer into the PDPT.
+	   %EAX is the total number of page directories.
+	   %EBX is where we build the PDPT entry. */
+2:
+	mov %esi, %ebx
+	and $0xFFFFF000, %ebx
+	or $0x3, %ebx
+
+	mov %ebx, (%edi)
+
+	add $0x1000, %esi
+	add $0x8, %edi
+	sub $0x1, %eax
+
+	cmp $0x0, %eax
+	jne 2b
+
+	/* STEP 4: initialise the page directories.
+	   Each page directory entry can be used to map 2MiB of virtual memory.
 	   The exact number of page directories in use is determined by BOOTSTRAP_PDIR_SIZE */
 
 	/* the total number of page directory entries is stored in %EAX */
@@ -160,24 +234,55 @@ init_page_tables:
 	   %EAX is the total number of page directories.
 	   %EBX is where we build the pagedir entry. */
 
-2:
+3:
 	mov %esi, %ebx
-	xor $0xFFF, %ebx
-	or $0x3, %ebx
+	and $0xFFFFF000, %ebx
+	or $0x83, %ebx
 
-	# skip the first 4 bytes of the 8-byte entry, leaving them zero.
-	add $0x4, %edi
 	mov %ebx, (%edi)
 
 	add $0x200000, %esi
-	add $0x4, %edi
-	dec %eax
-	jnz 2b
+	add $0x8, %edi
+	sub $0x1, %eax
+
+	cmp $0x0, %eax
+	jne 3b
 
 	ret
 
+.global long_mode_switch
+.type long_mode_switch, @function
 long_mode_switch:
-	ret
+	/* load %CR3 with the physical address of the PML4T */
+	mov $bootstrap_pml4t, %eax
+	mov %eax, %cr3
+
+	/* enable long mode and the syscall/sysret instructions */
+	movl $0xC0000080, %ecx
+	rdmsr
+	orl $0x00000101, %eax
+	wrmsr
+
+	lgdt (bootstrap_gdt_ptr)
+
+	mov %cr4, %ecx
+	orl $0x00000020, %ecx
+	mov %ecx, %cr4
+
+	mov %cr0, %ecx
+	orl $0x8000002a, %ecx
+	mov %ecx, %cr0
+
+	mov $0x10, %ax
+	mov %ax, %ds
+	mov %ax, %es
+	mov %ax, %fs
+	mov %ax, %gs
+
+	ljmpl $0x08, $start_64
+
+	cli
+	hlt
 
 .global _start
 .type _start, @function