Add Rust support for RISC-V arch

[nbdd0121]

No description provided.

[TheSven73]

Does this run on QEMU? If so, would it make sense to run this in the CI, like the other architectures?

[nbdd0121]

Does this run on QEMU? If so, would it make sense to run this in the CI, like the other architectures?

It runs on QEMU, but you need to supply a firmware (e.g. OpenSBI). I don't think any distro has that supplied yet, so it means in the CI we have to pull and compile another project, which isn't trivial amount of work.

[ojeda]

we have to pull and compile another project, which isn't trivial amount of work.

We are already cross-compiling Busybox on the fly -- does OpenSBI take long to compile? If not, I can take a look at adding it.

[memoryruins]

Ubuntu 20.04 (which I think CI uses) packages OpenSBI 0.6, 20.10 packages 0.8, and 21.04 packages 0.9.
The most recent version of OpenSBI is 0.9 if that matters.

[nbdd0121]

Ubuntu 20.04 (which I think CI uses) packages OpenSBI 0.6, 20.10 packages 0.8, and 21.04 packages 0.9.
The most recent version of OpenSBI is 0.9 if that matters.

Wow, Ubuntu has OpenSBI packaged, I didn't know that. Debian only has OpenSBI in sid, so I assumed Ubuntu wouldn't have it yet. I'll look to see if I can integrate it in the CI.

[ojeda]

Thanks @nbdd0121! If you see any problems or you do not have time, let me know and I can do the CI missing bits.

[nbdd0121]

@ojeda I had a try, but I got a timeout and GitHub killed it without giving me much information. I don't have any machines with Ubuntu 20.04, and I tried to use nektos/act to test locally but it does not seem to support some constructs used in the CI script. I don't have much experience debugging GitHub actions; could you have a look if you have time? Thanks.

[ojeda]

Sure! Let me take a look.

[ojeda]

The bundled OpenSBI works fine for me in a VM, so no need to recompile.

The timing out issue is because 1) CONFIG_SOC_VIRT is not enabled and 2) -no-reboot does not seem to work for RISC-V in that version of QEMU. I compiled the latest QEMU and it works there.

The no output issue is due to something missing in the configuration, defconfig works.

I think the best approach is merging this without enabling riscv in the CI matrix just yet, and then I can look into adding a newer QEMU and enabling it.

[ojeda]

I will likely tweak a few minor nits later on, but I think we can merge this as-is.

Thanks a lot!

Referencing #66.

[alex]

We should add this to arch-support.rst as well!

[ojeda]

Yeah! I will do it when actually enabling it in the CI matrix.