fdpp

what is fdpp?

fdpp is a 64-bit DOS core.
It is based on a FreeDOS kernel ported to modern C++.
In short, FreeDOS plus-plus.

Can be compiled with clang (not gcc!) and booted under dosemu2.

building and installing

Just run make.
For an out-of-tree build, run <path_to_fdpp>/configure before running make.
After compiling, run sudo make install to install.

installing from pre-built package

For the ubuntu package please visit this PPA. Fedora packages are here. OpenSUSE packages are here.

running

The simplest way to get it running is to use dosemu2.
Get the pre-built dosemu2 packages from ubuntu PPA or from COPR repo or from OpenSUSE repo or build it from sources.

configuration

fdpp uses fdppconf.sys file at boot. This file has the standard format of config.sys with some syntax extensions. It is fully backward-compatible with the DOSish config.sys, and if fdppconf.sys is missing, config.sys is attempted instead.

but what it actually is? why dosemu2?

fdpp is a user-space library that, as any DOS, can run DOS programs. Being a library, it can't act on its own and needs a host program to operate. This also means it can't be booted from the bare-metal PC, as the original freedos could.
The host program needs to provide a couple of call-backs for running real-mode code in v86 or similar environment. See this code as an example of providing call-backs to fdpp, and this code as an example of the boot loader. Sufficiently DOS-oriented kernels like freedos-32 or pdos/386 are the good candidates for running fdpp in the future.

what fdpp technically is?

A meta-compiler that was initially able to compile the freedos kernel from its almost unmodified sources. As the project evolves, the ability to compile freedos from the unmodified sources have lost its value and was dropped, as our copy of freedos is now heavily modified. As the result, the compiler is very small and is targeted only to our coding patterns.
The main tasks of it are to parse FAR pointers and generate thunks to real-mode asm code of freedos. As with any other compiler, fdpp is supplied with a small runtime support library and a dynamic linker.

compatibility

Simply put, fdpp runs every DOS program we tried, so the compatibility level is supposed to be very high. Better than that of most other known DOS clones, including FreeDOS.
If you find some compatibility problems, please report a bug.

portability

fdpp can work in any environment with STL/C++ runtime & minimal posix support. The build requirements are in line with today's posix-compatible environments: you'll need the full stack of tools like bison, autoconf, sed etc. Additionally you'll need a clang tool-chain as clang++ is the only compiler to build fdpp with. That said, building fdpp under itself may be a challenge. :)

related projects

FreeDOS

FreeDOS kernel is a DOS-compatible kernel that is used as a core of fdpp.

dosemu2

dosemu2 is a virtual machine that allows you to run DOS software under linux. It is a primary host platform for fdpp.

comcom32

comcom32 is a 32bit command.com that is supposed to be used with fdpp while we don't have a 64bit one.

similar projects

dosbox

dosbox has a good built-in DOS written in C++. It is tightly coupled to dosbox; you can't easily port it to your project, whereas fdpp is designed to be plugable. Also it uses host APIs and libraries for filesystem access, CD-ROM playing and similar things. fdpp uses no host APIs or libraries, which may be good or bad, depending on your use-case. dosbox is cleanly written in C++, whereas fdpp wraps the C-coded freedos kernel into a C++ framework, resulting in a nuclear C/C++ mix.

freedos-32 (inactive)

freedos-32 is a kernel written with DOS compatibility in mind. It has a rich user-space part with libc. Very good candidate for running fdpp. Unfortunately, the kernel was scrapped, and currently something else is being developed.

freedos-64 (inactive)

freedos-64 seems to be a project planning to implement a 64bit kernel around the real-mode freedos kernel.

NightKernel

NightKernel is A 32-bit drop-in replacement for the FreeDOS kernel, as they call themselves. In fact, it is an assembly-written ring-0 kernel, currently w/o any DOS compatibility at all. Can't be used to run fdpp because it doesn't support user-space add-ons.

PDOS/386

pdos/386 is a Public Domain Operating System with a user interface as simple as MSDOS. It supports a "theoretical 32-bit MSDOS API" (probably similar to that of 32-bit DOS extenders) and some of the Win32 API, allowing a subset of Windows executables to be run. PDOS/386 is good enough to run gcc, as, and ld to rebuild itself.
As for running fdpp - pdos/386 is a very promising project, but its author seems to be reluctant at adding v86 support, preferring to switch to real mode for bios calls. The lack of v86 leaves very small room for fdpp and for DOS programs in general unfortunately.