Dr. Brian Robert Callahan

Dr. Brian Robert Callahan

academic, developer, with an eye towards a brighter techno-social life

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2026-07-13

Get the source code here.

FreeBSD does not have a package for GDC, the GNU D Compiler, which is the D frontend of GCC. I frequently use GDC on FreeBSD as a research tool. As such, I had to actually bootstrap GDC for FreeBSD. I forgot to share how I did it; this post is intended to fix that.

It's very straightforward and easy. If you have DMD, then you can easily get GDC. I wrote a small wrapper program to make it as easy and quick as possible.

#### What GCC claims

GCC in their documentation says that GDC must be built with GDC. Specifically, they say, "In order to build GDC, the D compiler, you need a working GDC compiler (GCC version 9.4 or later) and D runtime library, 'libphobos', as the D front end is written in D." The documentation goes on to say, "Versions of GDC prior to 12 can be built with an ISO C++11 compiler, which can then be installed and used to bootstrap newer versions of the D front end."

Parts of that are inarguably true: GDC is written in D as of GCC 12. But parts of it feel untested: what is so special about GDC that it is the only D compiler that can build GDC? All the D compilers share a frontend, and the D frontend does not use any esoteric parts of the language. And even if it did, all three D compilers share a frontend, so in theory any D compiler should be able to bootstrap GDC. This is what I wanted to test, if for no other reason than it would take incredibly long to build an old version of GCC just to build a new version of GCC. It takes seconds to build DMD.

#### What reality demonstrates

In order to build GDC, you need a D compiler and libphobos version sufficient to build only the stage1 GDC. The stage1 GDC builds the stage1 libphobos. If we have a D compiler that can do just enough to build a working stage1 GDC, then we are golden. That's the only hurdle we need to overcome.

The DMD compiler, the reference D compiler, is perfectly capable of doing this. The impediment isn't whether or not DMD can build the stage1 GDC; it is the fact that of all three D compiler frontends, DMD, GDC, and LDC, they all use different flag sets. DMD and LDC are close to one another; GDC uses a very different flag style to match GCC. If we can write a small wrapper program that translates those flag differences, we should be able to build the stage1 GDC with DMD.

#### `gdc-wrapper`

The little program just mechanically translates flags, adds all the other arguments unchanged, and then calls DMD with the transformed argument list. I mostly went through trial-and-error until DMD built the stage1 GDC. I would just let the GDC build run and when something failed, I would add that flag to the wrapper. The most difficult flags to deal with were `-MF` and `-MT`, which create dependency rules files. What I did here was ignore `-MT` and create the file specified with `-MF` but with only a single newline character in it. That's a bit of a hack but we're not interested in getting it exactly right; we're interested in getting stage1 GDC built and moving on.

Other than that, we ignore warning flags, convert `-o output.o` to `-ofoutput.o`, change `-finline` to `-inline`, change `-fversion=VERSION` to `-version=VERSION`, and a few more small changes to make sure things linked correctly.

#### And it works

I downloaded the FreeBSD x86\_64 DMD 2.112.0 binaries from the D website, untarred it to my `HOME`, and then built `gdc-wrapper` with `./configure --dmd=/home/briancallahan/dmd2/freebsd/bin64/dmd && make` and I was able to build GDC without issue by adding `/home/briancallahan/gdc-wrapper` to the end of my `PATH` temporarily with `export PATH=$PATH:$PWD`. It really was that simple. I can build GDC 15.2.0 and GDC 16.1.0 with this on FreeBSD 15.

#### Conclusion

Hopefully this helps some FreeBSD, NetBSD, GNU Hurd, or Illumos people. Or anyone on a Linux distro that doesn't have a GDC package.

The obvious limitation is that for now, DMD only has backends for x86 and x86\_64 (though an ARM64 backend is on the way!). So if you want a GDC for a different CPU architecture, you will first need to bootstrap a native GDC with this procedure and then you can follow one of our previous posts to build a cross-GDC en route to a native GDC for a different CPU architecture.

[](https://briancallahan.net/blog/20260713.html#top)

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