actually jump to 'kernel'

README.md

@@ -0,0 +1,21 @@
+# bootler
+
+hobby bootloader written in asm. It's just for playing around... for now :p
+
+### memory map
+
++------ 0x00100000 ------+
+| hardware, bios stuff   |
++------ 0x00080000 ------+
+| pm stack (esp)         | from boot.asm
++------ 0x00010200 ------+
+| kernel (kernel.asm)    |
++------ 0x00010000 ------+
+| free                   |
++------ 0x00007E00 ------+
+| bootloader (boot.asm)  |
++------ 0x00007C00 ------+
+| real mode stack (sp)   | from boot.asm
++------ 0x00000500 ------+
+| bios stuff             |
++------ 0x00000000 ------+

boot.asm

@@ -1,27 +1,157 @@
-; yoinked from osdev.org
+; bootler
-mov ax, 0x07C0
+; 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
+mov ah, 0x0E
-cld
+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:
+; activate a20
-  lodsb
+mov ax, 0x2401
-  ; hang if at null terminator
+int 0x15
-  or al, al
+jc error
-  jz hang
 
-  ; BIOS interrupt prints al
+; load kernel
-  mov ah, 0x0E
+; 'docs' from https://www.ctyme.com/intr/rb-0607.htm
-  mov bh, 0
+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:
+  db 0x00
-    jmp hang
+  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

kernel.asm

@@ -0,0 +1,23 @@
+[bits 32]
+
+mov al, 'K'
+out dx, al
+mov al, 'e'
+out dx, al
+mov al, 'r'
+out dx, al
+mov al, 'n'
+out dx, al
+mov al, 'e'
+out dx, al
+mov al, 'l'
+out dx, al
+mov al, 0x0D
+out dx, al
+mov al, 0x0A
+out dx, al
+mov al, 0x00
+out dx, al
+jmp $
+
+times 512-($-$$) db 0

package.nix

@@ -11,7 +11,12 @@ in
     version = "0.1.0";
     src = ./.;
     buildPhase = ''
-      ${nasm}/bin/nasm boot.asm -o ${bootImg}
+      ${nasm}/bin/nasm boot.asm -o boot.bin
+      ${nasm}/bin/nasm kernel.asm -o kernel.bin
+
+      dd if=/dev/zero of=${bootImg} bs=512 count=2
+      dd if=boot.bin of=${bootImg} conv=notrunc
+      dd if=kernel.bin of=${bootImg} bs=512 seek=1 conv=notrunc
     '';
     installPhase = ''
       mkdir -p $out/bin
@@ -26,13 +31,10 @@ in
       cp $(echo $out)/bin/${bootImg} ./.bootler/${bootImg}
       chmod a+w ./.bootler/${bootImg}
 
-      echo "press any key to continue. Qemu will clear the screen..."
-      read -s -n 1
-
       # run image
       ${qemu}/bin/qemu-system-x86_64 \
         -nographic \
-        -hda ./.bootler/${bootImg}
+        -drive file=./.bootler/${bootImg},format=raw,index=0,media=disk
 
       # clean up
       rm ./.bootler -r