create disk image with gpt

boot0.s

@@ -3,11 +3,11 @@
 ; --------------------------------------------------------------------
 ; R | 0x000000 - 0x000400: real-mode interrupt vector table
 ; R | 0x000400 - 0x000500: bios data area
-; U | 0x000500 - 0x007000: stack
+; U | 0x000500 - 0x007c00: stack
-; U | 0x007000 - 0x007c00: globals
+; U |   0x007000 - 0x007c00: big stage0 initial stack frame
-;   |   0x007000 - 0x007001: boot drive number
+;   |     0x007000 - 0x007001: boot drive number
-;   |   0x007001 - 0x007002: number of hard disk drives
+;   |     0x007001 - 0x007002: boot drive sectors per track
-;   |   0x007002 - 0x007003: 
+;   |     0x007002 - 0x007004: boot drive number of heads
 ; U | 0x007c00 - 0x007e00: boot sector
 ; U | 0x007e00 - 0x080000: conventional usable memory
 ; R | 0x080000 - 0x0a0000: extended bios data area (maximum possible size)
@@ -17,7 +17,7 @@
 ; R | 0x0f0000 - 0x100000: motherboard bios
 
 ; BIOS puts our boot sector at 0000:7c00
-org 0x7c00  
+org 0x7c00
 ; We're (probably) in real mode
 bits 16 
 
@@ -29,26 +29,31 @@ bits 16
   mov ds, ax
   mov es, ax
 
-  ; Put stack base at 0x7000. Stack grows high->low, so we'll grow away from our program text at
+  ; We put stack base at 0x7c00 and give ourselves a big stack frame [0x7000,0x7c00) for spilling to.
-  ; 0x7c00. We reserve the range [0x7000,0x7c00) for globals.
+  ; Stack grows high->low, so we'll grow away from our program text at 0x7c00.
   mov ss, ax
-  mov sp, 0x7000
+  mov sp, 0x7c00
+  mov bp, 0x7000
 
   ; Segment for VGA (0xb800 * 16 = 0xb8000)
   mov ax, 0xb800
   mov fs, ax
 
-  mov di, 0x7000
-
   ; Store boot drive number
-  mov ds:[di], dl
+  mov [bp], dl
 
   ; Get drive geometry
   mov di, 0x00
   mov ah, 0x08
   int 0x13
   jb panic
-  mov ds:[di + 1], dl
+  and cl, 0x3f
+  mov [bp + 1], cl
+  movzx ax, dh
+  add ax, 1
+  mov [bp + 2], ax
+
+  
 
   ; Set VGA mode
   ; https://mendelson.org/wpdos/videomodes.txt
@@ -57,16 +62,17 @@ bits 16
 
   mov word fs:[0x0000], 0xc048
   mov word fs:[0x0002], 0xc069
-  mov word fs:[0x0004], 0xc021
   hlt
 
 panic:
   mov ax, 0x0003
   int 0x10
-  mov word fs:[0x0000], 0x4f46
+  mov ax, 0xb800
-  mov word fs:[0x0002], 0x4f41
+  mov ds, ax
-  mov word fs:[0x0004], 0x4f49
+  mov word [0x0000], 0x4f46
-  mov word fs:[0x0006], 0x4f4c
+  mov word [0x0002], 0x4f41
+  mov word [0x0004], 0x4f49
+  mov word [0x0006], 0x4f4c
   hlt
 
   ; TODO: enable A20
@@ -90,20 +96,3 @@ panic:
   %if ($ - $$) > 440
   %error "exceeded mbr bootstrap field size"
   %endif
-
-  ; Pad to the end of the MBR bootstrap field
-  times 440 - ($ - $$) db 0
-
-  ; Unique disk ID
-  dd 0x00000000
-  ; Reserved
-  dw 0x0000
-
-  ; Zero the partition fields
-  ; TODO: fill in the field pointing to the GPT table
-  times 510 - ($ - $$) db 0
-
-  ; Boot signature
-  db 0x55
-  db 0xaa
-

justfile

@@ -1,6 +1,16 @@
 run:
-  qemu-system-x86_64 -drive format=raw,file=boot0.bin
+  qemu-system-x86_64 -drive format=raw,file=disk.bin
 
 build:
   nasm -f bin -o boot0.bin boot0.s
 
+zero_disk:
+  dd if=/dev/zero of=disk.bin bs=64K count=16
+
+partition_disk:
+  parted --script disk.bin mklabel gpt
+  parted --script disk.bin mkpart test 34s 50%
+  parted --script disk.bin type 1 0fc63daf-8483-4772-8e79-3d69d8477de4
+
+write_stage0:
+  dd if=boot0.bin of=disk.bin conv=notrunc