initial commit

4 files changed, 356 insertions, 0 deletions

diff --git a/boot/bios.inc b/boot/bios.inc
new file mode 100644
index 0000000..ccc94e3
--- /dev/null
+++ b/boot/bios.inc
@@ -0,0 +1,128 @@
+macro bios_a20_enable {
+	mov ax, 0x2401
+	int 0x15
+}
+
+macro bios_vga_write_mode_3 {
+	mov ax, 0x03
+	int 0x10
+}
+
+; assumes dl = drive number
+macro bios_disk_read dst*, cyl*, head*, sector*, count*, err_label* {
+	local read_disk
+
+	assert 0 <= cyl    & cyl    <= 1023
+	assert 0 <= head   & head   <= 15
+	assert 1 <= sector & sector <= 17
+	assert 1 <= count  & count  <= 128
+
+	; try to read disk up to 3 times
+	mov di, 3
+
+read_disk:
+	; ah = 0x02, al = number of sectors to read
+	mov ax, (0x0200 or count)
+
+	; es:bx = pointer to destination buffer
+	if dst = 0
+		xor bx, bx
+	else
+		mov bx, dst
+	end if
+
+	; ch = track/cylinder number, cl = sector number
+	mov cx, ((cyl and 0xff) shl 8) or ((cyl and 0x300) shl 6) or sector
+
+	; dh = head number
+	if head = 0
+		xor dh, dh
+	else
+		mov dh, head
+	end if
+
+	int 0x13
+
+	jc .error
+	cmp ax, count
+	jne .error
+
+	jmp .exit
+.error:
+	dec di
+	jz err_label
+
+	; reset disk on error
+	xor ah, ah
+	stc
+	int 0x13
+	jc err_label
+	jmp read_disk
+.exit:
+}
+
+macro bios_e820_mmap mmap*, err_label* {
+	local e820, e820_entry
+e820:
+	virtual at di
+		label e820_entry
+		.base     dq ?
+		.length   dq ?
+		.type     dd ?
+		.ext_attr dd ?
+		.sizeof = $ - e820_entry
+	end virtual
+
+	mov di, mmap + 4
+	xor ebx, ebx
+	xor bp, bp
+
+	mov edx, 0x0534d4150
+	mov eax, 0xe820
+	mov byte [.ext_attr], 0x01
+	mov ecx, .sizeof
+	int 0x15
+	jc err_label
+
+	mov edx, 0x0534d4150
+	cmp eax, edx
+	jne err_label
+
+	test ebx, ebx
+	jz err_label
+
+	jmp @f
+
+.e820_loop:
+	mov ax, 0xe820
+	mov byte [.ext_attr], 0x01
+	mov ecx, .sizeof
+	int 0x15
+	jc err_label
+
+	mov edx, 0x0534d4150
+@@:
+	jcxz .skip_entry
+
+	; ACPI < 3.0
+	cmp cl, (.sizeof-4)
+	jbe .not_ext
+
+	; ignore data flag
+	test byte [.ext_attr], 0x01
+	jz .skip_entry
+
+.not_ext:
+	mov ecx, dword [.length]
+	or ecx, dword [.length + 4]
+	jz .skip_entry
+
+	inc bp
+	add di, .sizeof
+.skip_entry:
+	test ebx, ebx
+	jnz .e820_loop
+
+	; store e820 mmap entry count at beginning
+	mov [mmap], bp
+}
diff --git a/boot/boot.asm b/boot/boot.asm
new file mode 100644
index 0000000..eedde07
--- /dev/null
+++ b/boot/boot.asm
@@ -0,0 +1,144 @@
+format ELF64
+
+PML4_TABLE = 0x1000
+E820_MMAP  = 0xf000
+
+MSR_EFER   = 0xc0000080
+
+include 'bios.inc'
+include 'page.inc'
+include 'segdesc.inc'
+
+section '.text.boot' executable
+
+org 0x7c00
+use16
+	jmp far 0x0000:@f ; ensure cs = 0x0000
+@@:
+	xor ax, ax
+	mov ds, ax
+	mov es, ax
+
+	; put stack directly bellow bootloader
+	mov ss, ax
+	mov sp, $$
+	cld
+
+	mov [boot_disk], dl
+
+	bios_disk_read ($$+0x200), 0, 0, 2, 57, disk_error
+
+	bios_e820_mmap E820_MMAP, e820_error
+
+	bios_a20_enable
+	bios_vga_write_mode_3
+
+	page_table_init_real PML4_TABLE
+
+	; disable IRQs
+	mov al, 0xff
+	out 0xa1, al
+	out 0x21, al
+
+	lidt [dummy_idtr]
+
+	; enable PAE (1<<5) and PGE (1<<7)
+	mov eax, (1 shl 7) or (1 shl 5)
+	mov cr4, eax
+
+	; point cr3 at PML4
+	mov edx, edi
+	mov cr3, edx
+
+	; enable long mode
+	mov ecx, MSR_EFER
+	rdmsr
+	or eax, (1 shl 8)
+	wrmsr
+
+	; enable protected mode
+	mov ebx, cr0
+	or ebx, (1 shl 31) or (1 shl 0)
+	mov cr0, ebx
+
+	lgdt [gdtr]
+
+	jmp far (gdt.kcode-gdt):longmode
+
+e820_error:
+	; change beginning of error message ("disk" -> "e820")
+	mov dword [errmsg], 0x30323865
+disk_error:
+	mov si, errmsg
+	mov ah, 0x0e
+	jmp @f
+.loop:
+	int 0x10
+@@:
+	lodsb
+	test al, al
+	jnz .loop
+
+	; wait until keypress, then jump to reset vector (reboot)
+	xor ah, ah
+	int 0x16
+	jmp far 0xffff:0x0000
+
+use64
+longmode:
+	mov ax, (gdt.kdata-gdt)
+	mov ds, ax
+	mov es, ax
+	mov ss, ax
+
+	cli
+
+	; copy kernel to 0x100000
+	mov ecx, (57*0x200)/8
+	mov esi, 0x7e00
+	mov edi, 0x100000
+	rep movsq
+
+	xor eax, eax
+	xor ebx, ebx
+	xor ecx, ecx
+	xor edx, edx
+	xor edi, edi
+
+	; put stack at top of addressable memory
+	mov esp, 0x200000
+	mov ebp, esp
+
+	jmp 0x100000
+
+align 4
+dw 0
+label gdtr fword
+	.limit dw (gdt.sizeof - 1)
+	.addr  dd gdt
+
+align 4
+errmsg db "disk error: press any key to reboot",0
+
+align 8
+gdt:
+	.null dq 0
+	.kcode seg_desc 0, 0, (GDT_CODE_64 or SEG_PRIV0)
+	.kdata seg_desc 0, 0, (GDT_DATA_64 or SEG_PRIV0)
+	.ucode seg_desc 0, 0, (GDT_CODE_64 or SEG_PRIV3)
+	.udata seg_desc 0, 0, (GDT_DATA_64 or SEG_PRIV3)
+	.sizeof = $ - gdt
+
+align 4
+boot_disk db 0, 0
+label dummy_idtr fword
+	.limit dw 0
+	.addr  dd 0
+
+if ($-$$) <= 510
+	db 510-($-$$) dup 0
+else
+	display "ERR: boot sector image exceeds 512 bytes",10
+	assert ($-$$) <= 510
+end if
+db 0x55,0xaa
diff --git a/boot/page.inc b/boot/page.inc
new file mode 100644
index 0000000..ec2a8ad
--- /dev/null
+++ b/boot/page.inc
@@ -0,0 +1,44 @@
+PAGE_SIZE = 0x1000
+
+PAGE_PRESENT = (1 shl 0)
+PAGE_WRITE   = (1 shl 1)
+
+macro page_table_init_real pml4_table* {
+	local page_table
+
+	; zero out page table
+	mov edi, pml4_table
+	push di
+	mov ecx, (PAGE_SIZE*4)/4
+	xor eax, eax
+	cld
+	rep stosd
+	pop di
+
+	virtual at di
+		label page_table
+		.PML4T rb PAGE_SIZE
+		.PDPT  rb PAGE_SIZE
+		.PDT   rb PAGE_SIZE
+		.PT    rb PAGE_SIZE
+		.sizeof = $ - page_table
+	end virtual
+
+	; create first entry
+	mov word [.PML4T], (pml4_table + .PDPT - page_table) or PAGE_PRESENT or PAGE_WRITE
+	mov word [.PDPT],  (pml4_table + .PDT  - page_table) or PAGE_PRESENT or PAGE_WRITE
+	mov word [.PDT],   (pml4_table + .PT   - page_table) or PAGE_PRESENT or PAGE_WRITE
+
+	; identity map pages
+	push di
+	mov di, (pml4_table + .PT - page_table)
+	mov ax, (PAGE_PRESENT or PAGE_WRITE)
+@@:
+	mov [di], eax
+	add eax, PAGE_SIZE
+	add di, 8
+	cmp di, pml4_table + .sizeof
+	jb @b
+
+	pop di
+}
diff --git a/boot/segdesc.inc b/boot/segdesc.inc
new file mode 100644
index 0000000..b4d14dc
--- /dev/null
+++ b/boot/segdesc.inc
@@ -0,0 +1,40 @@
+; segment type
+SEG_ACCESSED     = 0001b
+SEG_CODE_READ    = 0010b
+SEG_DATA_WRITE   = 0010b
+SEG_CODE_CONFORM = 0100b
+SEG_DATA_EXPDOWN = 0100b
+SEG_EXECUTE      = 1000b
+
+; privilege level
+SEG_PRIV0 = (00b shl 0x05)
+SEG_PRIV1 = (01b shl 0x05)
+SEG_PRIV2 = (10b shl 0x05)
+SEG_PRIV3 = (11b shl 0x05)
+
+; other flags
+SEG_DESCTYPE = (1b shl 0x04) ; descriptor type
+SEG_PRES     = (1b shl 0x07) ; present
+SEG_SAVL     = (1b shl 0x0C) ; available for system use
+SEG_LONG     = (1b shl 0x0D) ; long mode
+SEG_SIZE     = (1b shl 0x0E) ; size
+SEG_GRAN     = (1b shl 0x0F) ; granularity
+
+; segment descriptor flag sets for convenience
+GDT_CODE_32 = SEG_DESCTYPE or SEG_PRES or SEG_SIZE or SEG_GRAN or SEG_EXECUTE or SEG_CODE_READ
+GDT_DATA_32 = SEG_DESCTYPE or SEG_PRES or SEG_SIZE or SEG_GRAN or SEG_DATA_WRITE
+GDT_CODE_64 = SEG_DESCTYPE or SEG_PRES or SEG_LONG or SEG_EXECUTE or SEG_CODE_READ
+GDT_DATA_64 = SEG_DESCTYPE or SEG_PRES or SEG_LONG or SEG_DATA_WRITE
+
+struc seg_desc base*, limit*, flag* {
+	assert 0x0 <= limit & limit <= 0x000fffff
+	assert 0x0 <= base  & base  <= 0xffffffff
+	assert (flag or 0xf0ff) = 0xf0ff
+
+	. dq ((limit shl 0x20) and 0x000f000000000000) or \
+	     ((flag  shl 0x28) and 0x00f0ff0000000000) or \
+	     ((base  shl 0x10) and 0x000000ff00000000) or \
+	     ((base  shl 0x20) and 0xff00000000000000) or \
+	     ((base  shl 0x10) and 0x00000000ffff0000) or \
+	     ((limit shl 0x00) and 0x000000000000ffff)
+}