Rust OpenSSL Cross Compile for Linux on Mac M1

cross-compile

# Install the toolchain
```
brew tap SergioBenitez/osxct
brew install x86_64-unknown-linux-gnu
```

# this should get installed in:
# /opt/homebrew/Cellar/x86_64-unknown-linux-gnu/

# Installing the macOS OpenSSL - if not already installed
```bash
brew install [email protected]
```

# this should get installed in:
# /opt/homebrew/Cellar/openssl\@1.1/

# Download the OpenSSL Source
```bash
cd /tmp
wget https://www.openssl.org/source/openssl-1.1.1n.tar.gz
cd openssl-1.1.1n
```

# Configure
```bash
CC="x86_64-unknown-linux-gnu-gcc -fPIE -pie" \
CXX="x86_64-unknown-linux-gnu-g++" \
AS="x86_64-unknown-linux-gnu-as" \
AR="x86_64-unknown-linux-gnu-ar" \
NM="x86_64-unknown-linux-gnu-nm" \
RANLIB="x86_64-unknown-linux-gnu-gcc-ranlib" \
LD="x86_64-unknown-linux-gnu-ld" \
STRIP="x86_64-unknown-linux-gnu-strip" \
./Configure linux-x86_64 no-shared no-async --prefix=/opt/homebrew/Cellar/openssl\@1.1/1.1.1n/x86_64-linux-gnu  --openssldir=/opt/homebrew/Cellar/openssl\@1.1/1.1.1n/x86_64-linux-gnu
```

# Make
```bash
make -j12
```

# Install
```bash
make install
```

# Now you should have a linux x86_64 version of openssl installed in:
# /opt/homebrew/Cellar/openssl\@1.1/1.1.1n/x86_64-linux-gnu

### Rust Cross compile in Mac for linux
# Now if you want to cross compile for linux on your mac m1 using rust with openssl or openss-sys
# Cargo.toml - as much as possible try to use "vendored" feature in openssl - that way the openssl will not become
# a dependancy on the target system

```bash
OPENSSL_INCLUDE_DIR=`brew --prefix [email protected]`/x86_64-linux-gnu/include OPENSSL_LIB_DIR=`brew --prefix [email protected]`/x86_64-linux-gnu/lib  OPENSSL_STATIC=1 cargo b --release --target x86_64-unknown-linux-gnu
```

# if you want to strip the executable:
```bash
x86_64-unknown-linux-gnu-strip target/release/<file>
```

more references:

1. https://stackoverflow.com/questions/71782250/cross-compile-error-ld-unknown-option-as-needed
2. https://github.dev/Homebrew/homebrew-core/tree/master/Formula
3. https://github.com/chinedufn/cross-compile-rust-from-mac-to-linux
4. https://users.rust-lang.org/t/cant-cross-compile-project-with-openssl/70922
5. https://betterprogramming.pub/cross-compiling-rust-from-mac-to-linux-7fad5a454ab1

key words:

1. platform specified libs (the openssl elf format) installed or built.
2. platform toolchains (gcc/linker...) installed.
3. set cc env, linker env for cross compile.
4. set openssl env for libs location.