From ef24568fed6f425c130447e8160dd1542459ddc5 Mon Sep 17 00:00:00 2001
From: John Tsiombikas <nuclear@member.fsf.org>
Date: Sun, 11 Aug 2024 02:51:35 +0300
Subject: [PATCH] fixed invalid data accesses, due to DS != SS, moved
 everything into the first 64k instead, should be enough for
 the kernel.

---
 kern/Makefile        |    3 ++-
 kern/src/main.c      |   12 ------------
 kern/src/startup.asm |    9 ++++-----
 3 files changed, 6 insertions(+), 18 deletions(-)

diff --git a/kern/Makefile b/kern/Makefile
index d097da2..187df0d 100644
--- a/kern/Makefile
+++ b/kern/Makefile
@@ -14,8 +14,9 @@ LD = ia16-elf-ld
 
 warn = -pedantic -Wall
 inc = -nostdinc -Isrc -Isrc/libc
+arch = -march=i8088 -mtune=i8088
 
-CFLAGS = -march=i8088 -mtune=i8088 $(warn) $(inc) -MMD
+CFLAGS = $(arch) -ffreestanding -mcmodel=small $(warn) $(inc) -MMD
 LDFLAGS = -T kern.ld -Map kern.map
 
 $(img): $(bin)
diff --git a/kern/src/main.c b/kern/src/main.c
index f89cd5d..cc3cd14 100644
--- a/kern/src/main.c
+++ b/kern/src/main.c
@@ -3,19 +3,7 @@
 
 void kmain(void)
 {
-	int i, j;
-	unsigned short __far *vmem = (void __far*)0xb8000000ul;
-	unsigned short c;
-
 	vid_init();
 	vid_text(0, 0, "hello!", VID_ATTR(LTRED, BLACK));
 	init_intr();
-
-	vmem += 80;
-	for(i=1; i<25; i++) {
-		c = ((i & 0xf) << 8) | '@';
-		for(j=0; j<80; j++) {
-			*vmem++ = c;
-		}
-	}
 }
diff --git a/kern/src/startup.asm b/kern/src/startup.asm
index c64684a..2cd9250 100644
--- a/kern/src/startup.asm
+++ b/kern/src/startup.asm
@@ -3,7 +3,7 @@
 	bits 16
 	section .startup
 
-; memory reserved at the top of RAM for the kernel stack
+; memory reserved at the top of the kernel segment for the stack
 STACKSZ equ 4096
 
 extern kmain
@@ -14,10 +14,9 @@ global _start
 _start:
 	; TODO floppy off if necessary
 
-	; move stack to the top of RAM (TODO: detect and avoid Ext. BIOS data area)
-	mov ax, (0xa0000 - STACKSZ) >> 4
-	mov ss, ax
-	mov sp, STACKSZ
+	; move stack to the top of the kernel segment
+	xor ax, ax
+	mov sp, ax
 
 	; zero .bss
 	mov di, _bss_start_off
-- 
1.7.10.4