Test aarch64-linux-android in emulator

[briansmith]

At the time we added 32-bit ARM Android to Travis CI, Aarch64 builds of Rust's libstd weren't available. However, now they are available, so we can add AAarch64 targets now.

[seankelly]

I looked into this and it requires an upgrade to the API level.

18 is less than minimum platform for arm64 (21)

[pietro]

I was hoping I'd be able to add Aarch64 after moving Android to clang because the clang wrapper script shipped by the Android NDK defines the ABI level used when installing it. As a temp hack we could define __ANDROID_API__ to 21 on Aarch64 builds and 18 on all other hardware archs.

[EternalDeiwos]

To do as @pietro suggests as a temporary hack, would it be as simple as changing the build.rs file to use API21 everywhere that it uses API18?

Please excuse the ignorance; I'm fairly new to Rust.

[briansmith]

To do as @pietro suggests as a temporary hack, would it be as simple as changing the build.rs file to use API21 everywhere that it uses API18?

    if target.os() == "android" {
        // Define __ANDROID_API__ to the Android API level we want.
        // Needed for Android NDK Unified Headers, see:
        // https://android.googlesource.com/platform/ndk/+/master/docs/UnifiedHeaders.md#Supporting-Unified-Headers-in-Your-Build-System
        let _ = c.define("__ANDROID_API__", Some("18"));
    }

Basically, instead of hard-coding 18, we need to select 18 for 32-bit ARM and 21 for 64-bit arm. The target architecture is in target.arch in this function.

I would accept a PR that did that.

[pietro]

@briansmith 759f1cc did that but it got reverted because my changes to add aarch64-linux-android ended up being a bust. Have you done any work on the travis/android setup? I have some time next week to look into this and the other issues ring is having with android on travis if you aren't already working on this.

[briansmith]

@briansmith 759f1cc did that

Thanks. I just cherry-picked that specific commit in ring's master branch now: 72397df

but it got reverted because my changes to add aarch64-linux-android ended up being a bust.

They were great! However, there was just some flakiness, which was probably a small issue.

I have some time next week to look into this and the other issues ring is having with android on travis if you aren't already working on this.

It would be great to get your help. Right now I'm working on getting the Android build working in Docker as I find directly working with Travis CI to be painful.

[briansmith]

@pietro Could you summarize what needs to happen to get aarch64 Android builds in CI, on top of your recent work? Would it be easier to do now?

[briansmith]

As of last year, we no longer define the Android API level to build for in build.rs; instead we expect the person building ring to have already configured tings for the API level they want. And, at the same time, we switched from GCC to clang. So, I think that it might be reasonable to revive this effort now.