Make armv7-android a tier-1 platform

[rillian]

I understand from the 1.13.0 stable release notes that ARM is currently considered a 2nd tier platform for Rust releases. Android is one of the major software platforms in the world today, and the mobile OS most open to third-party native code. Being able to target it is an important part of Rust's story.

More specifically, Firefox treats arm android as a tier-1 platform. Being able to rely on the same level of support in official rust releases would be a great aide in our deployment of Rust code in the Gecko rendering engine.

I therefore propose that armv7-linux-androideabi be promoted to tier-1.

[rillian]

This was inspired by rust-lang/rust#37691 just missing the release, and the corresponding warning about code generation on armhf in the release notes.

cc @alexcrichton, @kentuckyfriedtakahe.

[alexcrichton]

Ah yes of course! I actually had no idea armv7 Android was a tier 1 platform for Firefox. It's definitely a bad sign that Firefox has more tier 1 platforms than Rust! (or at least a certain cause of pain, as we're seeing).

The change we need to make armv7 tier 1 is likely to just add an auto bot running tests, which should hopefully become very easy very soon!

[dschaeffer]

Are there current plans for when armv7 Android will become a tier 1 platform for Rust?
This is currently preventing me from starting to adopt rust.

[eddyb]

I think we've been running tests on ARM for a while now? Not sure where the canonical tiers are defined though.

[arielb1]

We don't run the compiler on ARM tho, so we are vulnerable to unpleasantnesses such as rust-lang/rust#40593.

[dschaeffer]

so does the lack of response mean there are no current plans for making android a tier 1 platform?

[arielb1]

ARM is pretty much Tier 1.5 - running rustc on an armv7 host is not CI-tested (because that would require us to find a fast ARM build machine to do CI on), but compiling targeting armv7 is supported.

[dschaeffer]

@arielb1 That makes sense. Thanks for the explanation.

[infinity0]

BTW, it's possible to create a 32-bit armv7 ("armv8l") chroot on a fast 64-bit aarch64 machine, then run the rustc armv7 test suite inside that. It's what I've been doing on Debian. This isn't exactly androideabi but I imagine there's a quite a lot of overlap and fixing errors here could improve the android situation. I see test failures all the time on armhf(armv7) Debian unfortunately.

[arielb1]

@infinity0

For that, we'll need an armv8 build server. Our CI infrastructure is all in the cloud - do you know of good cloud ARMv8 servers?

[infinity0]

I don't personally know about them in detail, but you could ask ircs://irc.oftc.net/#debian-arm about what they're doing and/or browse the list of Debian machines here and contact the companies listed.

For tests.reproducible-builds.org we have some machines donated by codethink.co.uk. This isn't a public offer but it might be worth contacting them to see if they would do a similar thing for Rust.