Cross-compiling for OpenWrt with various programming languages

I have been messing about with the Nim programming language quite a lot recently. Because it compiles to C code, this means that it's very good for programming lots of devices - since most everything has a C compiler. I have to say that I am drawn to Nim's main goal of being efficient, because I dislike bloat. However, Nim has some disadvantages, and for me the biggest is that it has not reached a v1 release yet. So the language is not as stable as it could be, and I get nervous each time a new version of the compiler is released, wondering if my code will still work.

In fairness, Nim is quite stable, I don't want to be misleading. But until it reaches a version 1 release I will continue to be cautious. I would not use Nim for important work (yet) - although I am using it for hobbyist type stuff. And I've been enjoying it too.

But, in recent weeks I thought that it would be only fair for me to try out some other languages. So I've been doing some experiments on my linux box, mostly inside docker containers. Cross-compiling for embedded linux is high on my personal list of requirements, so I have been trying to target the latest stable release of OpenWrt (15.05.1) running on the Ralink RT5350F chipset. This can be done very easily with Nim. So, I tried that with a few other languages to see how I got on. Thank goodness for docker, it has made this process so much easier and when I'm finished it's very easy to tidy up my mess!

1. Go

At first, I thought that it was going to be easy with Go. It looked as simple as this command:

~# GOOS=linux GOARCH=mipsle /usr/local/go/bin/go build -v hello.go

Which looked all-good at first glance:

~# file hello
hello: ELF 32-bit LSB executable, MIPS, MIPS32 version 1 (SYSV), 
statically linked, not stripped

But when I ran it on my device, I just got this 'Illegal instruction' message:

~# /tmp/hello 
Illegal instruction
~# 

I then found several issues on the golang GitHub repo about MIPS32 support. So it looks like the easy way is not so easy after all. Anyway, I did eventually get a 'hello world' program cross compiled for OpenWrt with Go. And this time I was able to run the executable on my target device. In the end I followed the first set of these instructions. However, the resulting binary was 1.8 Mb just for the hello world program. At this point I decided to give up, and by that time I had read posts from other people saying that cross-compiling Go code for embedded devices resulted in binaries that were big and slow. Maybe in the future things will get better. I hope so.

2. Rust

It appears that Rust would be easier for cross-compiling to OpenWrt if I was using the trunk version of OpenWrt, because support for the target mipsel-unknown-linux-musl used by OpenWrt trunk is much better than mipsel-unknown-linux-uclibc which I need for the stable release (which I'm running). So I expect that this will become easier in time. In any case, this seems to work:

~# rustup target add mipsel-unknown-linux-musl
info: downloading component 'rust-std' for 'mipsel-unknown-linux-musl'
 15.3 MiB /  15.3 MiB (100 %)   1.5 MiB/s ETA:   0 s                
info: installing component 'rust-std' for 'mipsel-unknown-linux-musl'

Whereas this version (with uClibc) doesn't:

~# rustup target add mipsel-unknown-linux-uclibc
error: toolchain 'stable-x86_64-unknown-linux-gnu' does not contain 
component 'rust-std' for target 'mipsel-unknown-linux-uclibc'

So, maybe I should just try that again when I've moved onto a later version of OpenWrt (or one of the LEDE releases perhaps).

3. Vala

I found the Vala language by accident, but it is apparently used a lot by the Elementary OS project - which gives it some kudos in my book. Additionally, the syntax is very much like C#, which means it should be somewhat familiar to me. Like Nim, it also compiles to C so I thought that support for embedded linux should be good. However, it depends on some libraries (like GLib2) which I don't have available on my device. I could probably make this work if I wanted, but I had little interest in doing that. So I didn't proceed any further.

4. Crystal

I had a very brief look at Crystal which does have some support for cross-compiling. It looked interesting, although I found some of the syntax to be a bit strange in places. However I don't think it supports the target device I am looking for. But I did get this far, purely out of interest:

~# crystal build hello.cr --cross-compile --target "x86_64-unknown-linux-gnu"
cc hello.o -o hello  -rdynamic  -lpcre -lgc -lpthread 
/opt/crystal/src/ext/libcrystal.a -levent -lrt -ldl -L/usr/lib -L/usr/local/lib ~#

I didn't go any further than that, but it was interesting to have a little play.

In summary...

It actually looks like Nim is a pretty sensible choice for what I'm doing. In comparison to other languages it's amazingly simple to set up for cross-compilation. So maybe I just need to put up with any minor instabilities in syntax that are likely to appear. But it is a good reminder that I need to try Nim on OpenWrt trunk (or one of the LEDE releases), because they've moved from uClibc to musl. I don't know if that will introduce any issues. I need to come back to that...

At least in the short term I am happy to keep on messing about with Nim. And I'm happy that I have at least tried some alternatives. I will try to keep my eye on Go and Rust, both of which showed signs of promise. When I have a device running OpenWrt trunk, or LEDE, then perhaps I will give Rust another try.

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