A minimal x86 operating system that displays CPU information using the CPUID instruction.

• Boots via GRUB using Multiboot specification
• VGA text mode display with color support
• Screen scrolling implementation
• CPUID instruction wrapper
• Displays CPU vendor, family, model, stepping
• Shows processor feature flags (SSE, AVX, etc.)
• Binary and hexadecimal number formatting

• Target: x86 (32-bit protected mode)
• Bootloader: GRUB (Multiboot 0.6.96)
• Display: VGA text mode at 0xB8000
• Memory: 1MB kernel load address, 16KB stack

• Here's the previous repo cpuinfo-os

1. Fixed VGA buffer size (2000 vs 2200)
2. Proper screen scrolling instead of clearing
3. Corrected bit masking in CPUID parsing
4. Fixed CPUID inline assembly with proper constraints
5. Added CPUID availability check
6. Displays CPU vendor string (leaf 0x00)
7. Shows ECX feature flags (SSE3, AVX, AES, etc.)
8. Added hexadecimal printing function
9. Fixed binary printing for zero values
10. Increased stack from 4KB to 16KB
11. Added zig in the mix for additional or expermental things
12. Added -fno-omit-frame-pointer flag for better debugging
13. Added .gdbinit file for quicker and easier debugging with gdb

• GCC (with 32-bit support)
• GNU Binutils (as, ld)
• GRUB utilities (grub-mkrescue)
• QEMU (for testing)
• xorriso (dependency for grub-mkrescue)
• zig (for experimental things)

sudo apt install build-essential gcc-multilib grub-pc-bin xorriso qemu-system-x86 qemu-ui zig

sudo pacman -S base-devel grub xorriso qemu-arch-extra qemu-ui-sdl zig

make            # Build ISO
make run        # Build and run in QEMU
make clean      # Clean build artifacts
make debug      # Run with GDB debugging

# Assemble bootloader
as --32 src/bootloader/boot.s -o build/boot.o

# Compile kernel
gcc -m32 -c src/kernel/kernel.c -o build/kernel.o -ffreestanding -O2 -Wall -Wextra

# compiling zig objects
zig build-obj -target x86-freestanding -O ReleaseFast build/zigtest/hello.zig -femit-bin=build/hello.o

# Link
ld -m elf_i386 -T src/linker/linker.ld -o build/THBOS.bin build/boot.o build/kernel.o build/hello.o

# Create ISO
mkdir -p build/isodir/boot/grub
cp build/THBOS.bin build/isodir/boot/
cp src/bootloader/grub.cfg build/isodir/boot/grub/
grub-mkrescue -o THBOS.iso build/isodir

qemu-system-x86_64 -cdrom THBOS.iso -m 512M -display sdl

1. Create new VM (Type: Other, Version: Other/Unknown)
2. Disable EFI
3. Mount THBOS.iso as CD
4. Boot

Write ISO to USB:

sudo dd if=THBOS.iso of=/dev/sdX bs=4M status=progress

.
├── Makefile              # Build automation
├── README.md
└── src
    ├── bootloader
    │   ├── boot.s        # Assembly bootloader
    │   └── grub.cfg      # GRUB configuration
    ├── kernel
    │   ├── kernel.c      # Main kernel code
    │   └── kernel.h      # Type definitions and declarations
    ├── linker
    │   └── linker.ld     # Linker script
    └── zigtest
        └── hello.zig     # zig files (in testing)

0x00000000 - 0x000FFFFF: Real mode area (1MB)
0x00100000:              Kernel load address
0xB8000:                 VGA text buffer

• Resolution: 80×25 characters
• Format: 16-bit per character
  • Bits 0-7: ASCII character
  • Bits 8-11: Foreground color
  • Bits 12-15: Background color

• CPU vendor string (GenuineIntel, AuthenticAMD, etc.)
• Maximum supported CPUID leaf

• EAX: Stepping, Model, Family IDs
• EBX: Brand index, Cache line size, APIC ID
• ECX: SSE3, SSSE3, SSE4.1/4.2, AES, AVX, etc.
• EDX: FPU, VME, TSC, MSR, PAE, MMX, SSE, SSE2, etc.

# Terminal 1
qemu-system-i386 -cdrom build/THBOS.iso -m 512M -s -S

# Terminal 2
gdb build/THBOS.bin
(gdb) target remote localhost:1234
(gdb) break kernel_entry
(gdb) continue

THBoS provides a set of custom GDB shortcut commands (auto-loaded from .gdbinit) to make kernel debugging faster and more intuitive. These commands are designed for low-level OS development and work seamlessly with QEMU’s -s -S debug stub.

Start QEMU:

qemu-system-i386 -kernel build/THBOS.bin -m 512M -s -S

Start GDB:

gdb build/THBOS.bin

The custom .gdbinit in this project is auto-loaded and provides the commands documented below.

• Add this: set auto-load safe-path / into your ~/.config/gdb/gdbinit file
• These shortcuts only work when GDB loads the project’s .gdbinit.
• The kernel must be run with qemu-system-i386 to avoid architecture mismatches.

qemu-system-x86_64 -cdrom THBOS.iso -monitor stdio

• No interrupt handling (IDT)
• No keyboard input
• No disk I/O
• Uses GRUB's GDT (no custom GDT)
• No memory management
• Single-threaded
• No floating point support

1. IDT setup with interrupt handlers
2. Keyboard driver (IRQ1)
3. Timer (PIT) for scheduling
4. Custom GDT
5. Memory management (paging)
6. Shell interface
7. Extended CPUID leaves (cache info, thermal, etc.)
8. PCI device enumeration

• Intel® 64 and IA-32 Architectures Software Developer's Manual
• OSDev Wiki
• Multiboot Specification