[build] riscv64gc-unknown-linux-gnu target build error

[BohuTANG]

$ cargo install cross
$ cross build --target=riscv64gc-unknown-linux-gnu
info: syncing channel updates for 'nightly-2021-08-03-x86_64-unknown-linux-gnu'

  nightly-2021-08-03-x86_64-unknown-linux-gnu unchanged - rustc 1.56.0-nightly (e3b1c12be 2021-08-02)

info: checking for self-updates
   Compiling serde v1.0.130
   Compiling futures-util v0.3.17
   Compiling thiserror v1.0.28
   Compiling pin-project v1.0.8
   Compiling ring v0.16.20
   Compiling async-stream v0.3.2
   Compiling prost v0.8.0
   Compiling zeroize_derive v1.1.0
   Compiling multiversion v0.6.1
   Compiling enum-iterator v0.7.0
error: failed to run custom build command for `ring v0.16.20`

Caused by:
  process didn't exit successfully: `/target/debug/build/ring-fd514c25ce798ddb/build-script-build` (exit status: 101)
  --- stderr
  thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', /cargo/registry/src/github.com-1ecc6299db9ec823/ring-0.16.20/build.rs:358:10
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
warning: build failed, waiting for other jobs to finish...

Cargo tree:

cargo tree | grep -C 10  ring
│       │       ├── proc-macro2 v1.0.28 (*)
│       │       ├── quote v1.0.9 (*)
│       │       └── syn v1.0.74 (*)
│       ├── prost v0.8.0 (*)
│       ├── prost-derive v0.8.0 (proc-macro) (*)
│       ├── rustls-native-certs v0.5.0
│       │   ├── openssl-probe v0.1.4
│       │   └── rustls v0.19.1
│       │       ├── base64 v0.13.0
│       │       ├── log v0.4.14 (*)
│       │       ├── ring v0.16.20
│       │       │   ├── libc v0.2.101
│       │       │   ├── once_cell v1.8.0
│       │       │   ├── spin v0.5.2
│       │       │   └── untrusted v0.7.1
│       │       │   [build-dependencies]
│       │       │   └── cc v1.0.69 (*)
│       │       ├── sct v0.6.1
│       │       │   ├── ring v0.16.20 (*)
│       │       │   └── untrusted v0.7.1
│       │       └── webpki v0.21.4
│       │           ├── ring v0.16.20 (*)
│       │           └── untrusted v0.7.1
│       ├── tokio v1.11.0 (*)
│       ├── tokio-rustls v0.22.0
│       │   ├── rustls v0.19.1 (*)
│       │   ├── tokio v1.11.0 (*)
│       │   └── webpki v0.21.4 (*)
│       ├── tokio-stream v0.1.7
│       │   ├── futures-core v0.3.17
│       │   ├── pin-project-lite v0.2.7
│       │   └── tokio v1.11.0 (*)

Broken in rustls-native-certs crate.

[BohuTANG]

Related issue briansmith/ring#1182

[PsiACE]

ring is used in many dependencies, so the best way is to set tls as an optional feature.

fyi:

• Conditionally enable TLS only on supported platforms svenstaro/miniserve#580

[Xuanwo]

We don't provide riscv64gc support now, closing.