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