Update ci.yml to add support for loongarch64

[donmor]

What does this PR do

Add CI support for loongarch64 (re-implementation of #2023 ). Ioctl has been implemented in #2045 .

Checklist:

• I have read CONTRIBUTING.md
• I have written necessary tests and rustdoc comments
• A change log has been added if this PR modifies nix's API

[SteveLauC]

Please also add this target to the target support list of Nix as a tier2 target.

Please also add this.

[SteveLauC]

Any idea about this error?

error: failed to run `rustc` to learn about target-specific information

Caused by:
  process didn't exit successfully: `rustc - --crate-name ___ --print=file-names --cfg qemu -D warnings --target loongarch64-unknown-linux-gnu --crate-type bin --crate-type rlib --crate-type dylib --crate-type cdylib --crate-type staticlib --crate-type proc-macro --print=sysroot --print=split-debuginfo --print=crate-name --print=cfg` (exit status: 1)
  --- stderr
  error: Error loading target specification: Could not find specification for target "loongarch64-unknown-linux-gnu". Run `rustc --print target-list` for a list of built-in targets

[donmor]

Any idea about this error?

error: failed to run `rustc` to learn about target-specific information

Caused by:
  process didn't exit successfully: `rustc - --crate-name ___ --print=file-names --cfg qemu -D warnings --target loongarch64-unknown-linux-gnu --crate-type bin --crate-type rlib --crate-type dylib --crate-type cdylib --crate-type staticlib --crate-type proc-macro --print=sysroot --print=split-debuginfo --print=crate-name --print=cfg` (exit status: 1)
  --- stderr
  error: Error loading target specification: Could not find specification for target "loongarch64-unknown-linux-gnu". Run `rustc --print target-list` for a list of built-in targets

loongarch64-unknown-linux-gnu is not supported by rustc 1.69.

[SteveLauC]

We should not change the MSRV for an architecture, I think we should add a step that will overwrite the MSRV environment variable to 1.71.0 when ${{ matrix.target }} is loongarch64-unknown-linux-gnu, something like:

- name: change Rust toolchain version for Loongarch
  run: echo "MSRV=$(if [ '${{ matrix.target }}' = 'loongarch64-unknown-linux-gnu' ]; then echo '1.71.0'; else echo '${{ env.MSRV }}'; fi)" >> $GITHUB_ENV

[SteveLauC]

Ok, I have no idea why it still does not work, it should work according to the cross doc:

[target.aarch64-unknown-linux-gnu]
image.name = "alpine:edge"
image.toolchain = ["x86_64-unknown-linux-musl", "linux/arm64=aarch64-unknown-linux-musl"] # Defaults to `x86_64-unknown-linux-gnu`

[Fearyncess]

cross-rs/cross@8c86a98, probably it should use a git-snapshot version cross-rs.

[Fearyncess]

@donmor @SteveLauC

I have rewrite a new config for Loongarch64 CI, and it works. Unfortunately, I face a big problem with the QEMU and testcases below.
Loongarch64 need a newer QEMU after 7.1 version. But before QEMU supported la64, qemu has a commit that has disabled many PRCTL subcodes 3 yrs ago. This commit will cause test_prctl failed in some cases, due to these subcodes has been disabled in newer QEMU.

BTW, I guess some commits in QEMU can change some syscalls' behavior, that brings some weird test results... -> #2418

[SteveLauC]

Close as this will be superseded by #2509.