Cross compile rust-openssl for Raspberry Pi 2

Question

I am on a Debian machine and I want to cross compile a project for my Raspberry Pi 2. I've managed to do it for a simple hello world using rustup, but couldn't figure out how to cross compile the rust-openssl crate.

I have compiled openssl with arm-linux-gnueabihf-gcc and installed it in my home/opensslArm directory.

When I run

OPENSSL_LIB_DIR=/home/johann/opensslArm/lib OPENSSL_INCLUDE_DIR=/home/johann/opensslArm/include cargo build --target=armv7-unknown-linux-gnueabihf

I get this error:

failed to run custom build command for `openssl-sys-extras v0.7.11`
Process didn't exit successfully: `/home/johann/projects/test/target/debug/build/openssl-sys-extras-e1c84960cd35bc93/build-script-build` (exit code: 101)
--- stdout
TARGET = Some("armv7-unknown-linux-gnueabihf")
OPT_LEVEL = Some("0")
PROFILE = Some("debug")
TARGET = Some("armv7-unknown-linux-gnueabihf")
debug=true opt-level=0
HOST = Some("x86_64-unknown-linux-gnu")
TARGET = Some("armv7-unknown-linux-gnueabihf")
TARGET = Some("armv7-unknown-linux-gnueabihf")
HOST = Some("x86_64-unknown-linux-gnu")
CC_armv7-unknown-linux-gnueabihf = None
CC_armv7_unknown_linux_gnueabihf = None
TARGET_CC = None
CC = None
HOST = Some("x86_64-unknown-linux-gnu")
TARGET = Some("armv7-unknown-linux-gnueabihf")
HOST = Some("x86_64-unknown-linux-gnu")
CFLAGS_armv7-unknown-linux-gnueabihf = None
CFLAGS_armv7_unknown_linux_gnueabihf = None
TARGET_CFLAGS = None
CFLAGS = None
running: "arm-linux-gnueabihf-gcc" "-O0" "-ffunction-sections" "-fdata-sections" "-g" "-fPIC" "-march=armv7-a" "-o" "/home/johann/projects/test/target/armv7-unknown-linux-gnueabihf/debug/build/openssl-sys-extras-e1c84960cd35bc93/out/src/openssl_shim.o" "-c" "src/openssl_shim.c"
ExitStatus(ExitStatus(256))


command did not execute successfully, got: exit code: 1



--- stderr
In file included from src/openssl_shim.c:1:0:
/usr/include/openssl/hmac.h:61:34: fatal error: openssl/opensslconf.h: No such file or directory
compilation terminated.
thread '<main>' panicked at 'explicit panic', /home/johann/.cargo/registry/src/github.com-88ac128001ac3a9a/gcc-0.3.28/src/lib.rs:840
note: Run with `RUST_BACKTRACE=1` for a backtrace.

I get the same error if I export the variables in question.

I don't know exactly what I am supposed to do, I am not an expert in cross compiling. Has anyone managed to do this?

EDIT: I was using rust-openssl 0.7.11. Upgrading to 0.7.13 fixed this issue (I can now see cargo compiling rust-openssl dependencies without an error) but I have now another one:

error: linking with `arm-linux-gnueabihf-gcc` failed: exit code: 1
...

note: /usr/lib/gcc-cross/arm-linux-gnueabihf/5/../../../../arm-linux-gnueabihf/bin/ld: /home/johann/opensslArm/lib/libssl.a(s23_meth.o): relocation R_ARM_THM_MOVW_ABS_NC against `a local symbol' can not be used when making a shared object; recompile with -fPIC
/home/johann/opensslArm/lib/libssl.a: error adding symbols: Bad value

How can I add -fPIC flag? Should I recompile opensslArm with specific flags?

Answer 1

You must pass shared option when configuring openssl compilation (this will make -fPIC parameter be passed to the compiler).

Here is a sequence of commands that I used to test cross compiling a Rust program that prints the openssl version:

cd /tmp

wget https://www.openssl.org/source/openssl-1.0.1t.tar.gz
tar xzf openssl-1.0.1t.tar.gz
export MACHINE=armv7
export ARCH=arm
export CC=arm-linux-gnueabihf-gcc
cd openssl-1.0.1t && ./config shared && make && cd -

export OPENSSL_LIB_DIR=/tmp/openssl-1.0.1t/
export OPENSSL_INCLUDE_DIR=/tmp/openssl-1.0.1t/include
cargo new xx --bin
cd xx
mkdir .cargo
cat > .cargo/config << EOF
[target.armv7-unknown-linux-gnueabihf]
linker = "arm-linux-gnueabihf-gcc"
EOF

cat > src/main.rs << EOF
extern crate openssl;

fn main() {
    println!("{}", openssl::version::version())
}
EOF

cargo add openssl # requires cargo install cargo-add
cargo build --target armv7-unknown-linux-gnueabihf

Testing the compiled program on the host computer

Setting OPENSSL_STATIC makes rust-openssl be statically linked. If you use the static linked version of rust-openssl, install a libc for armhf (crossbuild-essential-armhf on Debian) and qemu-static, you can the run the compiled program with the command:

qemu-arm-static target/armv7-unknown-linux-gnueabihf/debug/xx

Answer 2

This is an older question but it shows up highly on Google, so I wanted to call out that nowadays you don't need to manually compile OpenSSL (if you don't want to). The openssl crate provides a vendored feature that causes OpenSSL to be compiled from source when you build your project.

You can propagate the feature into your own project to optionally depend on vendored by adding something like this to your Cargo.toml:

[features]
...

# If compiling on a system without OpenSSL installed, or cross-compiling for a different
# architecture, enable this feature to compile OpenSSL as part of the build.
# See https://docs.rs/openssl/#vendored for more.
static_ssl = ['openssl/vendored']

[dependencies]
...

[dependencies.openssl]
optional = true
version = ...

Enabling the static_ssl feature when building your project will then compile OpenSSL against the same target architecture as the rest of your build.

This post goes into some more details about different ways of compiling with OpenSSL.