rust-cross-openbsd

Cross-compiling Rust to OpenBSD (currently only i386/amd64).

Getting Rust to work on OpenBSD is currently a work in progress and is not easy to do. It requires that you track OpenBSD -current and to patch and build your own OpenBSD kernel and userland. If you don't know what that is, this is either a great opportunity for you to learn, or maybe you should wait until this process gets easier (i.e. the OpenBSD rthread patch lands).

OpenBSD Prerequisites

To start, you need to download and install an OpenBSD snapshot. Then you need to follow the instructions on how to check out -current and build it. After you have rebooted into -current, the next step is to patch librthreads and then rebuild your kernel and userland.

cd /usr/src
patch -p1 < patch-librthread

After patching, you need to rebuild your kernel and userland and reboot. After that, your OpenBSD -current system will have support for LLVM's segmented stacks. The next section will walk you through building stage1 on OpenBSD.

Stage 1 Prerequisites OpenBSD

Before you can build stage 1 on OpenBSD, you must compile and install a bunch of ports from source. Here is the list of ports:

• gcc-4.8.3
• python-2.7.8
• automake-1.14
• audoconf-2.69
• libtool
• gmake
• cmake
• perl
• git

When building gcc-4.8.3, make sure you do it like this:

cd /usr/ports/lang/gcc/4.8/
env FLAVOR="full" make
env FLAVOR="full" make install
env SUBPACKAGE="-c++" make install

This is necessary to make sure that both the C and C++ compilers are built and installed. Now you're ready to clone this repo and build stage 1.

After installing Python, make sure you add the symlinks to make it your default:

ln -sf /usr/local/bin/python-2.7 /usr/local/bin/python
ln -sf /usr/local/bin/python-2.7-2to3 /usr/local/bin/2to3
ln -sf /usr/local/bin/python-2.7-config /usr/local/bin/python-config

Stage 1 OpenBSD

The build process requires full clones of the Rust and LLVM code trees so make sure you do this on a partition with enough room. I think 3 GByte is probably sufficient. Now clone this repo locally:

cd /tmp
git clone https://github.com/dhuseby/rust-cross-openbsd

The stage1-openbsd.sh script will install some of the intermediate binaries in your /usr/local so you need to run this with enough privileges to install there. Also make sure that your PATH environment variable lists /usr/local/bin before anything else. Now, let's build stage 1:

cd rust-cross-openbsd
sudo ./stage1-openbsd.sh

The build script will take care of cloning all of the required code and patching things properly. The first thing it does is pull down a newer version of GNU binutils and build it. If you watch the output carefully, you'll notice that the binutils fails during the install pass. It's because I think newer versions of binutils use GPLv3 and is incompatible with the licensing requirements for OpenBSD and is therefor not maintained to support OpenBSD. The ld binary doesn't support OpenBSD, but that's OK, because all we need from binutils is a newer assember (e.g. as) that understands all of the pseudo-ops in the assembly files found in the Rust tree.

When the script is done, there will be a stage1-openbsd.tgz file that you need to copy to your Linux box and unpack it in the root folder of this repo there. I have included a build log of this called stage1-openbsd-build.log if you want to compare output.

Stage 1 Linux

Start off by cloning this repo somewhere with a few gigabytes of disk space:

cd /tmp
git clone https://github.com/dhuseby/rust-cross-openbsd
cd rust-cross-openbsd

Now kick off the stage1-linux.sh script:

./stage1-linux.sh

When that is done, everything should be ready to go to move to the second stage. I have included a build log of this called stage1-linux-build.log if you want to compare output.

Stage 2 Linux

Stage 2 on Linux requires the output of Stage 1 on OpenBSD and Stage 1 on Linux.
You should have copied the stage1-openbsd.tgz file to the root folder of the clone of this repo on your Linux machine. Unpack it now:

tar -zxvf stage1-openbsd.tgz

Then kick off the stage2-linux.sh script. The second stage takes the parts from Stage 1 on both machines and uses it to build the rust libraries and all of the .o files needed to link a rustc executable on OpenBSD.

When the script is done, it will have created a tarball named stage2-linux.tgz. Copy this tarball over to your OpenBSD machine and then continue on to Stage 3. I have included a build log file called stage2-linux-build.log if you want to compare output.

Stage 3 OpenBSD

Before you start Stage 3 you must unpack the stage2-linux.tgz tarball from earlier:

tar -zxvf stage2-linux.tgz

Now kick off Stage 3 on OpenBSD:

./stage3-openbsd.sh

NOTE: So far I have been unable to get this step to complete. I have included the build log from my last try. It is called stage3-openbsd-build.log. If you open it, you'll see that it fails to link. I'm pretty sure this means that Rust is impossible to cross-compile this way because OpenBSD's ld is an old GNU linker that doesn't understand all of the features needed to link rustc. It is not possible to compile a newer linker from binutils because the binutils linker no longer supports the OpenBSD platform due to licensing problems. So what can be done? Here are some ideas I might try:

1. Try using the same version of compiler, assembler, and linker on Linux as I am on OpenBSD. The idea is that the .o and .rlib files created during Stages 1 and 2 on Linux will not have anything in them that the old linker on OpenBSD won't understand. I think this is likely the easiest solution.
2. Instead of trying to build an OpenBSD executable, just build a Linux executable that knows how to cross-compile to OpenBSD. With Linux emulation on OpenBSD this will, in theory, allow the self-hosting rustc compiler to be built directly on OpenBSD.
3. The hardest solution of course is to figure out how to get the old OpenBSD linker to understand the newer features in the .o files so that it can successfully link the rustc.

So, I'm stumped at the moment. I would appreciate any help trying to figure this out. I think I've documented my process sufficiently here that it is easy to recreate elsewhere.