如何通过 Rust 在 Mac OS 上交叉编译 openssL 库？

Question

当我在MacOS上编译Linux二进制文件时，遇到了这个问题：看起来rust库“openssl-sys v0.9.61”绑定到了MacOS的C库。无法链接到linux。

cargo build --release --target=x86_64-unknown-linux-musl
   Compiling openssl-sys v0.9.61
error: failed to run custom build command for `openssl-sys v0.9.61`

Caused by:
  process didn't exit successfully: `~/test/../bin/release/build/openssl-sys-96148dcd52905249/build-script-main` (exit status: 101)
  --- stdout
  cargo:rustc-cfg=const_fn
  cargo:rerun-if-env-changed=X86_64_UNKNOWN_LINUX_MUSL_OPENSSL_LIB_DIR
  X86_64_UNKNOWN_LINUX_MUSL_OPENSSL_LIB_DIR unset
  cargo:rerun-if-env-changed=OPENSSL_LIB_DIR
  OPENSSL_LIB_DIR unset
  cargo:rerun-if-env-changed=X86_64_UNKNOWN_LINUX_MUSL_OPENSSL_INCLUDE_DIR
  X86_64_UNKNOWN_LINUX_MUSL_OPENSSL_INCLUDE_DIR unset
  cargo:rerun-if-env-changed=OPENSSL_INCLUDE_DIR
  OPENSSL_INCLUDE_DIR unset
  cargo:rerun-if-env-changed=X86_64_UNKNOWN_LINUX_MUSL_OPENSSL_DIR
  X86_64_UNKNOWN_LINUX_MUSL_OPENSSL_DIR unset
  cargo:rerun-if-env-changed=OPENSSL_DIR
  OPENSSL_DIR unset
  cargo:rerun-if-env-changed=OPENSSL_NO_PKG_CONFIG
  cargo:rerun-if-env-changed=PKG_CONFIG_ALLOW_CROSS_x86_64-unknown-linux-musl
  cargo:rerun-if-env-changed=PKG_CONFIG_ALLOW_CROSS_x86_64_unknown_linux_musl
  cargo:rerun-if-env-changed=TARGET_PKG_CONFIG_ALLOW_CROSS
  cargo:rerun-if-env-changed=PKG_CONFIG_ALLOW_CROSS
  cargo:rerun-if-env-changed=PKG_CONFIG_x86_64-unknown-linux-musl
  cargo:rerun-if-env-changed=PKG_CONFIG_x86_64_unknown_linux_musl
  cargo:rerun-if-env-changed=TARGET_PKG_CONFIG
  cargo:rerun-if-env-changed=PKG_CONFIG
  cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR_x86_64-unknown-linux-musl
  cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR_x86_64_unknown_linux_musl
  cargo:rerun-if-env-changed=TARGET_PKG_CONFIG_SYSROOT_DIR
  cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR
  run pkg_config fail: "pkg-config has not been configured to support cross-compilation.\n\n                Install a sysroot for the target platform and configure it via\n                PKG_CONFIG_SYSROOT_DIR and PKG_CONFIG_PATH, or install a\n                cross-compiling wrapper for pkg-config and set it via\n                PKG_CONFIG environment variable."

  --- stderr
  thread 'main' panicked at '

  Could not find directory of OpenSSL installation, and this `-sys` crate cannot
  proceed without this knowledge. If OpenSSL is installed and this crate had
  trouble finding it,  you can set the `OPENSSL_DIR` environment variable for the
  compilation process.

  Make sure you also have the development packages of openssl installed.
  For example, `libssl-dev` on Ubuntu or `openssl-devel` on Fedora.

  If you're in a situation where you think the directory *should* be found
  automatically, please open a bug at https://github.com/sfackler/rust-openssl
  and include information about your system as well as this message.

  $HOST = x86_64-apple-darwin
  $TARGET = x86_64-unknown-linux-musl
  openssl-sys = 0.9.61

  ', ~/.cargo/registry/src/openssl-sys-0.9.61/build/find_normal.rs:174:5
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

我发现有些人也遇到了这个问题： https://www.andrew-thorburn.com/cross-compiling-a-simple-rust-web-app/

Answer 1

第一步是确定哪个依赖项正在使用 openssl，您可以使用以下命令来执行此操作cargo tree：

cargo tree --target=x86_64-unknown-linux-musl -i openssl-sys

就我而言，这将rusoto_core板条箱识别为依赖于它的板条箱。有些 crate 可以使用功能标志进行编译，以使用备用 TLS 库，这使得它们比 OpenSSL 更易于使用。

例如，Rusotorustls在以下位置启用这样的功能Cargo.toml：

rusoto_core = {version = "0.42.0", default_features = false, features=["rustls"]}
rusoto_s3 = {version = "0.42.0", default_features = false, features=["rustls"]}
rusoto_sqs = {version = "0.42.0", default_features = false, features=["rustls"]}

在 Rusoto 案例中，有与 AWS Lambda 一起使用的交叉编译文档：https://rusoto.org/lambdas.html

或者，您也许可以向编译器提供交叉编译的 OpenSSL，但据我了解，目前这更加困难且记录不足。