From da41f6b0e29df2d365f0787fe7c7c02571172de5 Mon Sep 17 00:00:00 2001
From: Ain <41307858+nero@users.noreply.github.com>
Date: Thu, 23 Apr 2020 21:49:10 +0200
Subject: [PATCH] Rework early startup and fix bss memory reservation

---
 boot/kernel.asm | 71 ++++++++++++++++++++++++++++---------------------
 1 file changed, 40 insertions(+), 31 deletions(-)

diff --git a/boot/kernel.asm b/boot/kernel.asm
index 7b82cf0..ed565ed 100644
--- a/boot/kernel.asm
+++ b/boot/kernel.asm
@@ -255,50 +255,59 @@ fputc:	push ax
 	pop ax
 	iret
 
-main:	int 0x28
-	jmp main
+	; write CS:AX to ES:DI and advance DI
+	; used for setting interrupts
+stovec:	stosw
+	mov ax, cs
+	stosw
+	ret
+
+vects:	dw int20h, int21h, idle, fputc
+
+main:	mov si, vects
+	mov di, (0x20*4)
+	lodsw
+	call stovec
+	lodsw
+	call stovec
+	mov di, (0x28*4)
+	lodsw
+	call stovec
+	lodsw
+	call stovec
+
+	mov si, banner
+	mov ah, 9
+	int 0x21
+
+loop:	int 0x28
+	mov ah, 7
+	int 0x21
+	jz loop
+	int 0x29
+	jmp loop
 
 init:	cli
 	xor ax, ax
 	mov ds, ax
 	mov es, ax
 	mov ss, ax
-	xor sp, sp
+	mov sp, stacke
 
+	; relocate
 	mov si, 0x7C00
 	mov di, $$
 	mov cx, (init-$$)
 	rep movsb
 
-	; Set boot drive as current drive
-	call dnconv
-	call select
-
-	; Set int 0x20 to 0x2F
-	mov di, (0x20*4)
-	mov si, ivects+0x7C00-$$
-	mov cx, 0x10
-.loop:	movsw
-	mov ax, cs
-	stosw
-	loop .loop
-
-	mov si, banner
-	mov ah, 0x09
-	int 0x21
-
 	jmp 0:main
 
-ivects:	dw int20h, int21h, iret, iret
-	dw iret, iret, iret, iret
-	dw idle, fputc, iret, iret
-	dw iret, iret, iret, iret
-
 section .bss
-bpb:	times bpb_len resb 0
-drvnum:	resb 0
+bpb:	resb bpb_len
+drvnum:	resb 1
 	align 4
-drvoff:	resd 0 ; partition offset
-drvpos:	resd 0 ; absolute physical sector number
-buffer:	times 512 resb 0
-
+drvoff:	resd 1; partition offset
+drvpos:	resd 1; absolute physical sector number
+buffer:	resb 512
+stack:	resw 512
+stacke: