How do I cross-compile openssL libraries on Mac OS by rust?

Question

When I was compiling a Linux binary on MacOS, I encountered this problem: It looks like the rust library "openssl-sys v0.9.61" is bound to the C library of MacOS. can't link to 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

I found that some people also encountered this problem: https://www.andrew-thorburn.com/cross-compiling-a-simple-rust-web-app/

Answer 1

It's true that you need to determine which rust dependencies use openssl during the cross compile link phase. In my project, reqwest and mysql dependencies apparently use them when cross-compiling. I had a similar issue when cross-compiling from my mac to x86_64 or aarch64 (arm) linux targets on my mac m1. The linker was failing when linking to openssl.. The trick is to add openssl crate to your project. There is good information here: https://docs.rs/openssl/latest/openssl/

here are the steps with other helpful links also:

1.rustup add target  (this is AMD64 linux)
rustup target add x86_64-unknown-linux-musl

for (arm7 linux)
rustup target add aarch64-unknown-linux-musl



1(a) add the xplatform linker
brew install FiloSottile/musl-cross/musl-cross

for x86 and arm7 support:
brew install FiloSottile/musl-cross/musl-cross --with-aarch64 --with-x86_64

1(b) add openssl crate
https://docs.rs/openssl/latest/openssl/

may need to install openssl (see directions)
brew install openssl@1.1

[dependencies]
openssl = { version = "0.10", features = ["vendored"] }

2. modify ~/.cargo/config.toml

add link targets
[target.x86_64-unknown-linux-musl]
linker = "x86_64-linux-musl-gcc"

[target.aarch64-unknown-linux-musl]
linker = "aarch64-linux-musl-gcc"

[target.x86_64-unknown-linux-gnu]  - notneeded
linker = "x86_64-unknown-linux-gnu-gcc"

3. export TARGET_CC

x86_64:
export TARGET_CC=x86_64-linux-musl-gcc

for arm7:
export TARGET_CC=aarch64-linux-musl-gcc

4. compiling openssl
include the openssl crate:
openssl = { version = "0.10", features = ["vendored"] }

5. build for target
cargo build --target x86_64-unknown-linux-musl

cargo build --target aarch64-unknown-linux-musl

Answer 2

The first step is to determine which dependency is using openssl, which you can do with crate tree :

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

In my case this identified the rusoto_core crate as the one depending on it. Some crates can be compiled with feature flags to use alternate TLS libraries, making them easier to use than OpenSSL.

For example, Rusoto enables rustls like this in the 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"]}

In the Rusoto case, there is documentation for cross-compiling for use with AWS Lambda: https://rusoto.org/lambdas.html

Alternately, you may be able to provide cross-compiled OpenSSL to the compiler, but from what I understand this is more difficult and poorly documented at this time.