gcc-ia16 VS rust_dos

Mainstream GCC has never supported 16-bit code on x86, only 32-bit

However, there is (at least one) fork which adds 16-bit code support, see https://github.com/tkchia/gcc-ia16

I don't think the GCC maintainers have ever or will ever want to support 16-bit x86, because it is so limited, and adds a lot of messy corner cases, and nowadays is really only of hobbyist/retrocomputing interest.

Maybe there is some 16-bit x86 embedded system still being maintained–there were military spec versions of the 8086, and possibly some weapons system, aircraft, satellite, etc, still in use contains one. But I doubt they'd have any interest in adopting a 16-bit GCC – they'd already have some proprietary compiler they'd been using for decades, switching now would add a lot of risk, very late in the life of a legacy system, for no tangible benefit

These days there is also a 16-bit GCC port to DOS (https://github.com/tkchia/gcc-ia16). I never encountered one of those back in the day? I think the compiler itself does not run in 16-bit DOS though.

Anyone interested in compiling for DOS (32-bit or 16-bit) should also check out Free Pascal.

My advice is, when you feel you need that challenge, install DOSBox or DOSBox-X and Open Watcom C/C++, DJGPP, or gcc-ia16 and do some retro-programming. You'll also get the fun of being able to do low-level hardware twiddling and rely on DOS being so simple that it's effectively an RTOS.

Looking at part 1 and some of the videos, it looks like this doesn't actually use OpenWatcom, but i16gcc from the FreeDOS distribution, which looks to be a port of gcc that targets 16-bit x86.

And, if that surprises you, gcc-ia16 is a thing that has come into existence not only over a decade after DJGPP but also after Open Watcom already existed.

or GCC IA 16 (https://github.com/tkchia/gcc-ia16) gets someday mainlined (also a multi month/years project) and then gccrs can maybe use it as backend

There is a 16-bit port of GCC these days as well included together with DJGPP if you install FreeDOS, but available separately as well (I think it can cross-compile from other systems like DJGPP can too?) https://github.com/tkchia/gcc-ia16

TK Chia and others have been working on adding DOS C/C++ compiler-isms to GCC as well as improving the the codegen to make it more hospitable for DOS apps. So far, the FreeDOS kernel compilable by gcc-ia16.

https://github.com/tkchia/gcc-ia16

There is a more recent fork of gcc/DJGPP to make 16-bit DOS applications that I also never tried, but that might be worth using (and I think it is bundled in the latest FreeDOS, so it might be very easy to set up by just installing that in a virtual machine?): https://github.com/tkchia/gcc-ia16

You do not need segment registers much if you stick to the tiny model. Here is someone compiling Rust to a 16-bit DOS COM executable:

https://github.com/o8vm/rust_dos

Not sure what the approach would be for them to expand that to support segments.

In DJGPP there are macros to allow your protected mode application access physical real-mode addresses (like when you want to write to video RAM). I don't know if IA-16 also does something like that, or if they added far/near keywords to the language like old 16-bit C compilers did (at least the ones I used).

Free Pascal has helper-functions to work with segment+offset pointer pairs, also without having to modify the language itself. I think that would work well enough in C, but I guess the old method of adding non-standard keywords was seen as slightly more convenient.

Demo: https://github.com/o8vm/rust_dos

It is probably possible for almost any old platform with some cross-compilation magic, but not anything that will be officially supported as the compiler-makers focus on modern systems. There is for instance an unofficial 16-bit DOS backend for GCC and at least one or two projects to compile Rust to DOS-executables (that I assume use Clang?) (in addition to 32-bit DJGPP(gcc) for MSDOS that I linked to above). Probably are similar projects to target 68k somewhere?