Likely none. Well, I guess that's kind of an oversimplification though so here's the detailed story: We require some per-target integration to provide correct

Likely none. Well, I guess that's kind of an oversimplification though so here's the detailed story: We require some per-target integration to provide correct version(ARM), version(linux) statements in D code and we need to know the size of a mutex on the target system. Iain is currently rewriting this code here: https://github.com/D-Programming-GDC/GDC/pull/500 https://github.com/D-Programming-GDC/GDC/pull/500 However, we already provide and the new, rewritten code will continue to provide this integration for many targets. For example, all debian targets should be working: https://packages.debian.org/experimental/gdc https://packages.debian.org/experimental/gdc The main problem with architecture support is porting the runtime library and phobos. Here ARM is supported, MIPS and PPC has seen some work from LDC devs but making this work fully on GDC might require some small changes, MinGW is broken (and was never fully supported). One caveat thought is that all D compilers mainly target 32 or 64 bit systems. So things won't just work without changes for 8bit targets, although we've seen proof of concept D code on 8bit and 16bit CPUs as well.