actually jump to 'kernel'

boot.asm

@@ -1,28 +1,158 @@
-; yoinked from osdev.org
-mov ax, 0x07C0
+; bootler
+; legacy bootloader in nasm-flavoured asm
+; 2026 Andromeda
+; GPL licensed
+
+[bits 16]
+[org 0x7C00] ; address where bootloader is loaded
+
+xor ax, ax
 mov ds, ax
+mov es, ax
+mov ss, ax
+mov sp, 0x7C00
 
-mov si, msg
-cld
+mov ah, 0x0E
+mov al, 'R'
+int 0x10
+mov al, 'e'
+int 0x10
+mov al, 'a'
+int 0x10
+mov al, 'l'
+int 0x10
+mov al, 0x0D
+int 0x10
+mov al, 0x0A
+int 0x10
+mov al, 0x00 ; stops serial and bios output from overlapping in qemu -nographic
+int 0x10     ; output
 
-ch_loop:
-  lodsb
-  ; hang if at null terminator
-  or al, al
-  jz hang
+; activate a20
+mov ax, 0x2401
+int 0x15
+jc error
 
-  ; BIOS interrupt prints al
-  mov ah, 0x0E
-  mov bh, 0
+; load kernel
+; 'docs' from https://www.ctyme.com/intr/rb-0607.htm
+mov ah, 0x02
+mov al, 1 ; number of sectors to read (must be nonzero)
+mov ch, 0 ; low eight bits of cylinder number
+mov cl, 2 ; sector number 1-63 (bits 0-5); high two bits of cylinder (bits 6-7,
+          ; hard disk only)
+mov dh, 0 ; head number
+; dl is already set by bios
+mov bx, 0x1000 ; data buffer
+mov es, bx
+xor bx, bx
+int 0x13 ; read disk
+jc error
+
+; load gdt
+lgdt [gdt_descriptor]
+
+; jump to pm
+cli
+mov eax, cr0
+or eax, 1
+mov cr0, eax
+jmp 0x08:pm_start
+
+error:
+  mov al, 'e'
   int 0x10
+  mov al, 'r'
+  int 0x10
+  mov al, 'r'
+  int 0x10
+  mov al, 'o'
+  int 0x10
+  mov al, 'r'
+  int 0x10
+  jmp $
 
-  jmp ch_loop
+gdt_data:
+  ; null segment
+  dq 0x0000000000000000
+  ; code segment
+  dw 0xFFFF
+  dw 0x0000
 
-hang:
-    jmp hang
+  db 0x00
+  db 10011010b ; 32-bit code segment, present, ring 0
+  db 11001111b ; limit bits 16-19
+  db 0x00
 
-msg db 'Hello World', 0
+  ; data segment
+  dw 0xFFFF
+  dw 0x0000
 
+  db 0x00
+  db 10010010b ; 32-bit data segment, present, ring 0
+  db 11001111b ; limit bits 16-19
+  db 0x00
+
+gdt_descriptor:
+  dw $ - gdt_data - 1 ; size
+  dd gdt_data         ; start
+
+[bits 32]
+
+; entry point
+pm_start:
+  ; data segment registers
+  mov ax, 0x10
+  mov ds, ax
+  mov es, ax
+  mov fs, ax
+  mov gs, ax
+  mov ss, ax
+  mov esp, 0x80000
+
+  ; TODO actually configure COM1
+  mov dx, 0x3F8 ; COM1
+  mov al, 'P'
+  out dx, al
+  mov al, 'r'
+  out dx, al
+  mov al, 'o'
+  out dx, al
+  mov al, 't'
+  out dx, al
+  mov al, 'e'
+  out dx, al
+  mov al, 'c'
+  out dx, al
+  mov al, 't'
+  out dx, al
+  mov al, 'e'
+  out dx, al
+  mov al, 'd'
+  out dx, al
+  mov al, 0x0D
+  out dx, al
+  mov al, 0x0A
+  out dx, al
+
+  jmp 0x08:0x10000
+
+pm_error:
+  mov al, 'p'
+  out dx, al
+  mov al, 'm'
+  out dx, al
+  mov al, 'e'
+  out dx, al
+  mov al, 'r'
+  out dx, al
+  mov al, 'r'
+  out dx, al
+  mov al, 'o'
+  out dx, al
+  mov al, 'r'
+  out dx, al
+  jmp $
+  
 times 510-($-$$) db 0 ; 2 bytes less now
 db 0x55
 db 0xAA