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https://github.com/jayschwa/dos.zig

Create DOS programs with Zig
https://github.com/jayschwa/dos.zig

dos retrocomputing zig

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Create DOS programs with Zig

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README 

        
**Note**: [Zig 0.12.0 removed "bring your own OS" support](https://ziglang.org/download/0.12.0/release-notes.html#Bring-Your-Own-OS-API-Layer-Regressed)

from the standard library. This project will remain paused on Zig 0.11.0 until

a newer Zig release reintroduces BYOS support.



---



# DOS SDK for Zig



Write and cross-compile [DOS](https://wikipedia.org/wiki/DOS) programs with the

[Zig programming language](https://ziglang.org). Programs run in 32-bit

[protected mode](https://wikipedia.org/wiki/Protected_mode) and require a

resident [DPMI host](https://wikipedia.org/wiki/DOS_Protected_Mode_Interface).

[CWSDPMI](https://sandmann.dotster.com/cwsdpmi) is bundled with the executable

for environments that do not have DPMI available.



To comply with the [CWSDPMI license](https://sandmann.dotster.com/cwsdpmi/cwsdpmi.txt),

published programs must provide notice to users that they have the right to

receive the source code and/or binary updates for CWSDPMI. Distributors should

indicate a site for the source in their documentation.



This package is in a primordial state. It is a minimal demonstration of how to

create a simple DOS program with Zig. Only basic file/terminal input/output are

working, and does not include proper error handling. It will require hacking if

you wish to adapt it for your own needs.



## Quick Start



Install:



- [Zig](https://ziglang.org) (version 0.11.0)

- [DOSBox](https://www.dosbox.com)



Run:



``` sh

zig build run

```



## Design



There are five main components of this package:



- [DOS API](https://stanislavs.org/helppc/int_21.html) wrappers call the 16-bit

  real mode interrupt 21 routines (via DPMI) and implement operating system

  interfaces for the Zig standard library.

- [DPMI API](http://www.delorie.com/djgpp/doc/dpmi) wrappers manage extended

  memory blocks and segments.

- A custom [linker script](https://sourceware.org/binutils/docs/ld/Scripts.html)

  produces [DJGPP COFF](http://www.delorie.com/djgpp/doc/coff) executables.

- The [CWSDPMI](https://sandmann.dotster.com/cwsdpmi) stub loader enters

  protected mode and runs the COFF executable attached to it.

- A small demo program exercises all of the above.



## Roadmap



- Proper error handling.

- Parse environment data (command, variables) and hook into standard library abstractions.

- Implement `mprotect` for stack guard and zero pages.

- Implement a `page_allocator` for the standard library.

- Add graphical demo program.



## Questions and Answers



### Can I just target 16-bit real mode rather than require DPMI?



It is technically possible, but not a goal of this package. Zig (via LLVM) can

generate "16-bit" code using the `code16` ABI target. In reality, this code is

often 32-bit instructions with added prefixes that override the address or

operand size. Using `code16` actually produces *larger* binaries. Additionally,

the oldest CPU that can be targeted is an Intel 80386, which supports 32-bit

protected mode. It's guaranteed to be there and has a lot of advantages, so we

might as well use it.



### Why not integrate with an existing DOS toolchain like DJGPP?



This was attempted and had mixed results. DJGPP's object format (COFF) is

subtly different from the one produced by modern toolchains such as Zig. Crude

conversion scripts had to be used to get them to work together and it was not

robust. While it would be nice to leverage DJGPP's C library, it ultimately

felt like more trouble than it was worth. Not relying on a separate toolchain

will make things easier in the long run.