Hello world

doc/internal/gdt.txt

@@ -0,0 +1,3 @@
+0x08: 0x0000.0000 - 0x0007.ffff (code)
+0x10: 0x0000.0000 - 0x0007.ffff (data)
+0x18: 0x0003.8000 - 0x0003.ffff (stack)

doc/internal/mem.txt

@@ -0,0 +1,4 @@
+0x0001.0000 - 0x0002.ffff: unused
+0x0003.0000 - 0x0003.7fff: kernel
+0x0003.8000 - 0x0003.ffff: stack
+0x0004.0000 - 0x0007.ffff: unused

makefile

@@ -0,0 +1,21 @@
+floppy: kernel boot
+	mkdir -p obj out
+	/sbin/mkfs.fat -C -R 17 -n "PORTLAND OS" obj/shadow.img 1440
+	echo -n -e '\xeb\x3c' > obj/jmp.bin
+	dd if=obj/jmp.bin of=obj/shadow.img obs=2 conv=notrunc
+	dd if=out/boot.bin of=obj/shadow.img obs=1 seek=62 conv=notrunc
+	dd if=out/kernel.bin of=obj/shadow.img seek=1 conv=notrunc
+	mv obj/shadow.img out/floppy.img
+
+kernel:
+	mkdir -p obj/kernel out
+	gcc -m32 -ffreestanding -c src/kernel/main.c -o obj/kernel/main.o
+	gcc -m32 -ffreestanding -c src/kernel/vga.c  -o obj/kernel/vga.o
+	ld -T src/kernel/link.ld obj/kernel/main.o obj/kernel/vga.o -o out/kernel.bin
+
+boot:
+	mkdir -p out
+	nasm src/boot.asm -o out/boot.bin
+
+clean:
+	rm -r obj out

src/boot.asm

@@ -0,0 +1,55 @@
+bits 16
+org 0x7c3e
+
+kernel_sectors equ 16
+kernel_segment equ 0x3000
+
+  in al, 0x92
+  or al, 0x02
+  out 0x92, al
+
+  xor ax, ax
+  mov ss, ax
+  mov sp, 0x7ffc
+
+  mov ax, kernel_segment
+  mov es, ax
+  mov ax, 0x0200 + kernel_sectors
+  xor bx, bx
+  mov cx, 0x0002
+  xor dh, dh
+  int 0x13
+
+  cli
+
+  lgdt [gdt]
+
+  mov eax, cr0
+  or al, 0x01
+  mov cr0, eax
+
+  jmp 0x08:pmode
+
+bits 32
+
+pmode:
+  mov ax, 0x10
+  mov ds, ax
+  mov ax, 0x18
+  mov ss, ax
+  mov sp, 0x7ffc
+
+  jmp kernel_segment * 16
+
+gdt:
+  dw .e - .t
+  dd .t
+.t:
+  dq 0x0000_0000_0000_0000
+  dq 0x00c0_9a00_0000_007f
+  dq 0x00c0_9200_0000_007f
+  dq 0x0040_9203_8000_7fff
+.e:
+
+times $$ + 448 - $ db 0
+dw 0xaa55

src/kernel/link.ld

@@ -0,0 +1,15 @@
+OUTPUT_FORMAT(binary)
+OUTPUT_ARCH(i386)
+
+SECTIONS {
+  . = 0x00030000;
+  .entry : {
+    */main.o(.text)
+  }
+  .bin : {
+    *(.text)
+    *(.rodata)
+    *(.data)
+    *(.bss)
+  }
+}

src/kernel/main.c

@@ -0,0 +1,7 @@
+#include <stdint.h>
+#include "vga.h"
+
+void main() {
+  while (1)
+    vga_printsz("Hello! ");
+}

src/kernel/vga.c

@@ -0,0 +1,14 @@
+#include <stdint.h>
+
+#define VGA_START (uint16_t *)0x000b8000
+#define VGA_END (VGA_START + 80 * 25)
+uint16_t *cursor = VGA_START;
+uint16_t color = 0x1f00;
+
+void vga_printsz(uint8_t *sz) {
+  while (*sz) {
+    *(cursor++) = color | *(sz++);
+    if (cursor == VGA_END)
+      cursor = VGA_START;
+  }
+}

src/kernel/vga.h

@@ -0,0 +1,3 @@
+#include <stdint.h>
+
+void vga_printsz(uint8_t *sz);