ci: add armv7 target

[delta1]

Adds the armv7-unknown-linux-gnueabihf target to CI strategy matrix, but fails to compile secp256kfun_parity_backend in cargo test, even though cargo build works?

cargo build --target armv7-unknown-linux-gnueabihf -p secp256kfun_parity_backend -> works

cargo test --target armv7-unknown-linux-gnueabihf -p secp256kfun_parity_backend -> fails

[delta1]

@LLFourn if you approve the workflow you'll see the relevant error

[nickfarrow]

Does adding this to .cargo/config help?

# You need to install the "arm-none-linux-gnueabihf" linker on your system
[target.armv7-unknown-linux-gnueabihf]
linker = "arm-none-linux-gnueabihf-gcc"

It gets me to a different error

    Finished test [unoptimized + debuginfo] target(s) in 0.02s
     Running unittests src/lib.rs (/home/nick/repos/secp256kfun/target/armv7-unknown-linux-gnueabihf/debug/deps/secp256kfun_parity_backend-94ce32d7b35c0a66)
error: test failed, to rerun pass '-p secp256kfun_parity_backend --lib'

Caused by:
  could not execute process `/home/nick/repos/secp256kfun/target/armv7-unknown-linux-gnueabihf/debug/deps/secp256kfun_parity_backend-94ce32d7b35c0a66` (never executed)

Or is that just because i'm on the wrong architecture?

Whereas on my RPi I get running 0 tests.

Maybe we need to add linker to CI too somehow?

[delta1]

Hey @nickfarrow thanks for the suggestions, you gave me the idea to use cargo cross, which is working and showing the error fixed in https://github.com/LLFourn/elliptic-curves/pull/1

Here's the example workflow run: https://github.com/delta1/secp256kfun/runs/8135135847?check_suite_focus=true

[delta1]

Updated, but some builds failed. I think their cache was restored from the wrong target

You can see the failures here: https://github.com/delta1/secp256kfun/runs/8186507180?check_suite_focus=true

[delta1]

I think their cache was restored from the wrong target

Updated the rust-cache action to v2

[LLFourn]

LGTM. Thanks @delta1!