A very tiny OS written in Zig, which can be run on QEMU.

• Zig 0.13
• Fun
• only ~110 LoC
  • Zig : 37 Loc
  • Zig Build : 31 LoC
  • Assembly : 31 Loc
  • Linker Script : 25 Loc
• Very minimalist
• Easy to understand
• Great for Learning
• Altought does not anything useful it shows how Zig can be used to write an OS
• POC

./build.sh

./run.sh

boot.s (Assembly)

1. Bootloader (like GRUB) finds the Multiboot header
2. Loads the kernel into memory at 1MB (as specified in link.ld)
3. Jumps to _start
4. _start calls Zig kmain() function
5. kernel takes control and runs

link.ld (Linker Script)

1. Declares _start as the program's entry point
2. When a bootloader loads the kernel, it will jump to this symbol
3. This corresponds to the _start label in boot.s assembly file
4. Memory Layout Configuration
5. SECTIONS block defines how sections are arranged in memory
6. . = 1M sets the location counter to 1 megabyte
7. 1MB is chosen because it's above the first megabyte, which contains:

• Real-mode interrupt vectors (0x0000-0x03FF)
• BIOS data area (0x0400-0x04FF)
• Video memory (0xA0000-0xFFFFF)
• BIOS ROM (0xF0000-0xFFFFF)

8. Section Organization - Text Section (Executable Code)
9. .text: Contains all executable code
10. Bootloaders scan the first 8KB for this header
11. Data Section (Initialized Data)
12. .data: Contains initialized global and static variables

1. Compilation: source files are compiled into object files
2. Linking: The linker uses this script to combine object files
3. Memory Layout: Creates a binary with this structure:

0x100000 (1MB): Multiboot header
                kernel code (_start, kmain, etc.)
                Read-only data (strings, constants)
                Initialized variables
                Space reserved for uninitialized variables

4. Bootloader: Loads the binary at 1MB, finds the Multiboot header, jumps to _start
5. Execution: kernel runs starting from the _start symbol