kernel: Generalize startup code into main

Makefile

@@ -1,7 +0,0 @@
-default: nbp.com
-
-%.com: %.asm
-	nasm -s -o $@ $<
-
-clean:
-	rm -f *.com

kernel/Makefile

@@ -0,0 +1,7 @@
+default: kernel.com
+
+kernel.com: *.asm
+	nasm -s -o kernel.com main.asm
+
+clean:
+	rm -f *.com

kernel/main.asm

@@ -1,3 +1,53 @@
+; assumptions about the starting envionment
+cpu 8086
+org 0x0000
+
+_startup:
+  xor ax, ax ; trash ax
+  mov ax, cs
+  cmp ax, 0x0000 ; MBR or NBP, CS=0000 IP=7C00
+  je .mbr
+  cmp ax, 0x07C0 ;  MBR on weird BIOS, CS=07C0 IP=0000
+  je .mbr
+.dos:
+  ; ROP because call only works on immediate or memory
+  mov ax, cs
+  push ax ; return CS
+  mov ax, .dosret
+  add ax, 0x0100
+  push ax ; return IP
+  mov ax, cs
+  add ax, 0x0010
+  push ax ; main CS
+  mov ax, main
+  push ax ; main IP
+  retf
+.dosret:
+  int 0x20
+  jmp .halt
+.mbr:
+  push si ; index of partition table entry
+  push ds ; segment for ^
+  push dx ; dl might contain drive number
+  push bx ; possible offset for pxeenv+ struct
+  push es ; segment for ^
+
+  mov ax, 0x0050
+  mov es, ax
+  mov di, 0x0000
+
+  xor ax, ax
+  mov ds, ax
+  mov si, 0x7C00
+
+  mov cx, _reloc_end
+  rep movsb
+
+  call 0x0050:main
+.halt:
+  hlt
+  jmp .halt
+
 main:
   mov ax, cs
   mov ds, ax
@@ -10,10 +60,12 @@ main:
 
   retf
 
-%include "kernel/heap.asm"
-%include "kernel/intr.asm"
-%include "kernel/debug.asm"
-%include "kernel/kprintf.asm"
+%include "heap.asm"
+%include "intr.asm"
+%include "debug.asm"
+%include "kprintf.asm"
+
+_reloc_end:
 
 align 16
 heap:

kernel/test-pxenbp.sh

@@ -1,5 +1,5 @@
 #!/bin/sh
-exec qemu-system-x86_64 -boot n -fda fd0.img \
+exec qemu-system-x86_64 -boot n \
 	-option-rom /usr/share/qemu/pxe-rtl8139.rom \
 	-device e1000,netdev=mynet0,mac=52:54:00:12:34:56 \
-	-netdev user,id=mynet0,net=192.168.76.0/24,dhcpstart=192.168.76.9,tftp=$PWD,bootfile=nbp.com
+	-netdev user,id=mynet0,net=192.168.76.0/24,dhcpstart=192.168.76.9,tftp=$PWD,bootfile=kernel.com

nbp.asm

@@ -1,59 +0,0 @@
-; assumptions about the starting envionment
-cpu 8086
-org 0x0000
-; es:bx		pxeenv+ structure
-; ss:sp		functional stack
-
-_startup:
-  xor ax, ax
-  mov ax, cs
-  cmp ax, 0x0000 ; MBR or NBP, CS=0000 IP=7C00
-  je .mbr
-  cmp ax, 0x07C0 ;  MBR on weird BIOS, CS=07C0 IP=0000
-  je .mbr
-.dos:
-  mov ax, cs
-  push ax ; return CS
-  mov ax, .dosret
-  add ax, 0x0100
-  push ax ; return IP
-
-  mov ax, cs
-  add ax, 0x0010
-  push ax ; main CS
-  mov ax, main
-  push ax ; main IP
-  retf
-.dosret:
-  int 0x20
-  int 0x18
-.mbr:
-  mov ax, 0x0050
-  mov ds, ax
-  mov [0xFFFE], ss ; save current stack configuration onto new stack
-  mov [0xFFFC], sp
-  mov ss, ax
-  mov sp, 0xFFFC
-
-  push dx
-  push bx ; possible far ptr to pxeenv+ struct
-  push es
-
-  mov es, ax ; 0x0050
-  mov di, 0x0000
-
-  xor ax, ax
-  mov ds, ax
-  mov si, 0x7C00
-
-  mov cx, _reloc_end
-  rep movsb
-
-  call 0x0050:main
-.halt:
-  hlt
-  jmp .halt
-
-%include "kernel/main.asm"
-
-_reloc_end: