From f2899b62b997aafc25666f21ea3a754030a8de71 Mon Sep 17 00:00:00 2001
From: Elizabeth Alexander Hunt <me@liz.coffee>
Date: Mon, 28 Sep 2026 21:08:07 -0700
Subject: Upload from https://github.com/TheHuddle/pr-practice/pull/10/changes

---
 .gitignore |  5 +++++
 Makefile   | 30 ++++++++++++++++++++++++++++++
 boot.asm   | 29 +++++++++++++++++++++++++++++
 kernel.c   | 36 ++++++++++++++++++++++++++++++++++++
 linker.ld  | 43 +++++++++++++++++++++++++++++++++++++++++++
 readme.org | 15 +++++++++++++++
 6 files changed, 158 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Makefile
 create mode 100644 boot.asm
 create mode 100644 kernel.c
 create mode 100644 linker.ld
 create mode 100644 readme.org

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..5acb32e
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,5 @@
+iso/*
+*.o
+*.bin
+*.iso
+
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..c06ff32
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,30 @@
+.DEFAULT_GOAL := os.iso
+.PHONY: demo
+
+OBJECTS=entry.o kernel.o
+KERNEL_BUILD_FLAGS=-std=c99 -ffreestanding -O0 -Wall -Wextra
+OS_BUILD_FLAGS=-ffreestanding -O2 -nostdlib -lgcc
+
+entry.o: boot.asm 
+	nasm -felf32 boot.asm -o entry.o
+
+kernel.o: kernel.c
+	i386-elf-gcc -c kernel.c -o kernel.o $(KERNEL_BUILD_FLAGS)
+
+os.bin: kernel.o entry.o
+	i386-elf-gcc -T linker.ld -o os.bin $(OS_BUILD_FLAGS) $(OBJECTS)
+
+os.iso: os.bin
+	mkdir -p iso/boot/grub
+	cp os.bin iso/boot/os.bin
+	printf "menuentry 'HelloOS' {\n  multiboot /boot/os.bin\n  set gfxpayload=text\n}" > iso/boot/grub/grub.cfg
+	grub-mkrescue -o os.iso iso
+
+demo:
+	qemu-system-i386 demo/os.iso
+
+run: os.iso
+	qemu-system-i386 os.iso
+
+clean:
+	rm -rf iso os.iso *.o *.bin
diff --git a/boot.asm b/boot.asm
new file mode 100644
index 0000000..1627135
--- /dev/null
+++ b/boot.asm
@@ -0,0 +1,29 @@
+MBALIGN equ 1 << 0
+MEMINFO equ 1 << 1
+FLAGS equ MBALIGN | MEMINFO
+MAGIC equ 0x1BADB002
+CHECKSUM equ -(MAGIC + FLAGS)
+
+section .multiboot
+align 4
+  dd MAGIC
+  dd FLAGS
+  dd CHECKSUM
+
+section .bss
+align 16
+stack_bottom:
+resb 16384
+stack_top:
+
+section .text
+global _start:function (_start.end - _start)
+_start:
+  mov esp, stack_top
+    extern kernel
+  call kernel
+  cli
+
+jmp $
+
+.end:
diff --git a/kernel.c b/kernel.c
new file mode 100644
index 0000000..190d36e
--- /dev/null
+++ b/kernel.c
@@ -0,0 +1,36 @@
+#include <stddef.h>
+#include <stdint.h>
+
+#define WIDTH 80
+#define HEIGHT 25
+
+#define BLACK 0
+#define BLUE 1
+#define GREEN 2
+#define RED 4
+#define MAGENTA 13
+#define WHITE 15
+
+int strlen(char* s) {
+  int n = 0;
+  char* s_ptr = s;
+  while (*(s_ptr++)) { 
+    n++;
+  }
+  return n;
+}
+
+void kernel(void) {
+  uint16_t* vgamem = (uint16_t*) 0xB8000;
+  uint16_t vgacolors[6] = {WHITE | RED << 4, WHITE | GREEN << 4, WHITE | BLUE << 4, BLACK | RED << 4, BLACK | GREEN << 4, BLACK | BLUE << 4};
+  char* s = "Hello world!";
+  int i,j,k;
+  for (k = 0; k >= 0; ++k) {
+    k = (k % 5);
+    j = 0;
+    while (j < 100000000) { j++; } // Since we don't have an interrupt descriptor table we can't use the PIC; this emulates "sleeping"
+    for (i = 0; i < WIDTH*HEIGHT; i++) {
+      vgamem[i] = s[i % strlen(s)] | vgacolors[(i+k) % 6] << 8;
+    }
+  }
+}
diff --git a/linker.ld b/linker.ld
new file mode 100644
index 0000000..38ddd94
--- /dev/null
+++ b/linker.ld
@@ -0,0 +1,43 @@
+/* The bootloader will look at this image and start execution at the symbol
+   designated as the entry point. */
+ENTRY(_start)
+ 
+/* Tell where the various sections of the object files will be put in the final
+   kernel image. */
+SECTIONS
+{
+	/* Begin putting sections at 1 MiB, a conventional place for kernels to be
+	   loaded at by the bootloader. */
+	. = 1M;
+ 
+	/* First put the multiboot header, as it is required to be put very early
+	   early in the image or the bootloader won't recognize the file format.
+	   Next we'll put the .text section. */
+	.text BLOCK(4K) : ALIGN(4K)
+	{
+		*(.multiboot)
+		*(.text)
+	}
+ 
+	/* Read-only data. */
+	.rodata BLOCK(4K) : ALIGN(4K)
+	{
+		*(.rodata)
+	}
+ 
+	/* Read-write data (initialized) */
+	.data BLOCK(4K) : ALIGN(4K)
+	{
+		*(.data)
+	}
+ 
+	/* Read-write data (uninitialized) and stack */
+	.bss BLOCK(4K) : ALIGN(4K)
+	{
+		*(COMMON)
+		*(.bss)
+	}
+ 
+	/* The compiler may produce other sections, by default it will put them in
+	   a segment with the same name. Simply add stuff here as needed. */
+}
diff --git a/readme.org b/readme.org
new file mode 100644
index 0000000..161a39f
--- /dev/null
+++ b/readme.org
@@ -0,0 +1,15 @@
+* HelloOS
+This is a simple 32 bit protected mode operating system that runs in VGA mode. It outputs "Hello world" with some cool christmas lights.
+
+#+ATTR_HTML: :style margin-left: auto; margin-right: auto;
+[[https://s10.gifyu.com/images/demo45e010936937dd16.gif]]
+
+** Building
+In order to build this program you must have the ~i386~ GCC cross-compiled on your system. Instructions can be found on the [[https://wiki.osdev.org/GCC_Cross-Compiler][OSDev Wiki]]. You will also need ~grub~ and ~nasm~.
+
+Then, a simple ~make~ will generate the iso. You can run the iso by ~dd~'ing it to a usb stick or by running it with ~qemu-system-i386~. If you are running on native hardware make sure to boot it with BIOS (some PC's call it Legacy Support).
+
+** Using pre-compiled image
+This project contains a pre-compiled iso file in ~demo~. Simply ~cd demo~ and ~qemu-system-i386 os.iso~ or run ~make demo~.
+
+
-- 
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