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I'm trying to cross-compile a Rust binary with Docker for raspberry-pi on ARM6 architecture. I'm specifying the environment arguments for Cargo prior to building, but it errors out on a specific library saying that the "-m64" argument was not found.

The environment arguments when the error happens are different than what I set up in the Dockerfile; why are they being reset?

FROM ubuntu:latest



RUN apt-get update && 

    apt-get install 

    --yes 

    binutils 

    build-essential 

    curl 

    git 

    wget 

    libudev-dev 

    zip



ARG RASPBERRY_PI_TOOLS_COMMIT_ID=5caa7046982f0539cf5380f94da04b31129ed521

ENV CC=arm-linux-gnueabihf-gcc

ENV TARGET=arm-unknown-linux-gnueabihf

ENV CARGO_CFG_TARGET_ARCH=arm

ENV CARGO_CFG_TARGET_ENDIAN=little

ENV CARGO_CFG_TARGET_ENV=gnu

ENV CARGO_CFG_TARGET_FAMILY=unix

ENV CARGO_CFG_TARGET_OS=linux

ENV CARGO_CFG_TARGET_POINTER_WIDTH=32

ENV CARGO_FEATURE_DEFAULT=1

ENV CARGO_FEATURE_DEV_URANDOM_FALLBACK=1

ENV CARGO_FEATURE_RSA_SIGNING=1

ENV CARGO_FEATURE_USE_HEAP=1

ENV LD=/usr/bin/arm-linux-gnueabihf-ld

ENV LD_LIBRARY_PATH=/src/parity/target/release/deps:/root/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib:/root/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib

ENV QEMU_LD_PREFIX=/usr/arm-linux-gnueabihf/libc

RUN wget https://github.com/raspberrypi/tools/archive/$RASPBERRY_PI_TOOLS_COMMIT_ID.zip -O /root/pi-tools.zip

RUN unzip /root/pi-tools.zip -d /root

RUN mv /root/tools-$RASPBERRY_PI_TOOLS_COMMIT_ID /root/pi-tools

ENV PATH=/root/pi-tools/arm-bcm2708/arm-linux-gnueabihf/bin:$PATH

ENV PATH=/root/pi-tools/arm-bcm2708/arm-linux-gnueabihf/libexec/gcc/arm-linux-gnueabihf/4.8.3:$PATH



# Install Rust.

RUN curl https://sh.rustup.rs -sSf | sh -s -- -y --verbose

ENV PATH=/root/.cargo/bin:$PATH



# Install the arm target for Rust.

RUN rustup target add arm-unknown-linux-gnueabihf

# Configure the linker for the arm target.

ENV PKG_CONFIG_ALLOW_CROSS=1 

RUN echo '[target.arm-unknown-linux-gnueabihf]nlinker = "arm-linux-gnueabihf-gcc"' >> /root/.cargo/config



ENV USER=root

RUN cargo new /src

WORKDIR /src

RUN git clone https://github.com/paritytech/parity && cd parity && 

    /root/.cargo/bin/rustup target add arm-unknown-linux-gnueabihf && 

    /root/.cargo/bin/cargo build --target=arm-unknown-linux-gnueabihf --release --features final



# Verify that the output file is for armv6

RUN readelf --arch-specific ./target/arm-unknown-linux-gnueabihf/debug/src



RUN file /build/parity/target/armv7-unknown-linux-gnueabihf/release/parity



EXPOSE 8080 8545 8180

ENTRYPOINT ["/build/parity/target/armv7-unknown-linux-gnueabihf/release/parity"]

The error is:

process didn't exit successfully: `/src/parity/target/release/build/backtrace-sys-3c9a41016b6512eb/build-script-build` (exit code: 101)

--- stdout

TARGET = Some("x86_64-unknown-linux-gnu")

OPT_LEVEL = Some("3")

HOST = Some("x86_64-unknown-linux-gnu")

CC_x86_64-unknown-linux-gnu = None

CC_x86_64_unknown_linux_gnu = None

HOST_CC = None

CC = Some("arm-linux-gnueabihf-gcc")

CFLAGS_x86_64-unknown-linux-gnu = None

CFLAGS_x86_64_unknown_linux_gnu = None

HOST_CFLAGS = None

CFLAGS = None

DEBUG = Some("false")

running: "arm-linux-gnueabihf-gcc" "-O3" "-ffunction-sections" "-fdata-sections" "-fPIC" "-m64" "-I" "src/libbacktrace" "-I" "/src/parity/target/release/build/backtrace-sys-5fc2d3da7fb5f8d4/out" "-fvisibility=hidden" "-DBACKTRACE_ELF_SIZE=64" "-DBACKTRACE_SUPPORTED=1" "-DBACKTRACE_USES_MALLOC=1" "-DBACKTRACE_SUPPORTS_THREADS=0" "-DBACKTRACE_SUPPORTS_DATA=0" "-DHAVE_DL_ITERATE_PHDR=1" "-D_GNU_SOURCE=1" "-D_LARGE_FILES=1" "-Dbacktrace_full=__rbt_backtrace_full" "-Dbacktrace_dwarf_add=__rbt_backtrace_dwarf_add" "-Dbacktrace_initialize=__rbt_backtrace_initialize" "-Dbacktrace_pcinfo=__rbt_backtrace_pcinfo" "-Dbacktrace_syminfo=__rbt_backtrace_syminfo" "-Dbacktrace_get_view=__rbt_backtrace_get_view" "-Dbacktrace_release_view=__rbt_backtrace_release_view" "-Dbacktrace_alloc=__rbt_backtrace_alloc" "-Dbacktrace_free=__rbt_backtrace_free" "-Dbacktrace_vector_finish=__rbt_backtrace_vector_finish" "-Dbacktrace_vector_grow=__rbt_backtrace_vector_grow" "-Dbacktrace_vector_release=__rbt_backtrace_vector_release" "-Dbacktrace_close=__rbt_backtrace_close" "-Dbacktrace_open=__rbt_backtrace_open" "-Dbacktrace_print=__rbt_backtrace_print" "-Dbacktrace_simple=__rbt_backtrace_simple" "-Dbacktrace_qsort=__rbt_backtrace_qsort" "-Dbacktrace_create_state=__rbt_backtrace_create_state" "-Dbacktrace_uncompress_zdebug=__rbt_backtrace_uncompress_zdebug" "-o" "/src/parity/target/release/build/backtrace-sys-5fc2d3da7fb5f8d4/out/src/libbacktrace/alloc.o" "-c" "src/libbacktrace/alloc.c"

cargo:warning=arm-linux-gnueabihf-gcc: error: unrecognized command line option '-m64'

exit code: 1

--- stderr

thread 'main

I've set my ENV TARGET=arm-unknown-linux-gnueabihf in the Dockerfile, but when the error happens and it complains about not understanding what -m64 is, it's compiling for a TARGET = Some("x86_64-unknown-linux-gnu"), which is not the target I specified.

How do I make compilation use the original target I specified in the Dockerfile?

This is the dockerhub build

TARGET isn't used by Cargo. Cargo can be configured by environment variables as follows:

Cargo can also be configured through environment variables in addition to the TOML syntax above. For each configuration key above of the form foo.bar the environment variable CARGO_FOO_BAR can also be used to define the value. For example the build.jobs key can also be defined by CARGO_BUILD_JOBS.

Source

You are confused by an environment variable that Cargo set for your build script:

Cargo sets several environment variables when build scripts are run. Because these variables are not yet set when the build script is compiled, the above example using env! won't work and instead you'll need to retrieve the values when the build script is run:

TARGET - the target triple that is being compiled for. Native code should be compiled for this triple. Some more information about target triples can be found in clang’s own documentation.

Source

To fix your docker script do:

ENV CARGO_BUILD_TARGET=arm-unknown-linux-gnueabihf

See:

• How can I set default build target for Cargo?

I should've been compiling to armhv7 which is compatible with the Raspberry Pi 3 Model B.

This is a Dockerfile that compiles the parity binary for armhv7:

FROM debian:latest



RUN apt-get update && apt-get install -y --no-install-recommends 

    build-essential 

    ca-certificates 

    cmake 

    curl 

    git 

    pkg-config 

    gcc-arm-linux-gnueabihf 

    g++-arm-linux-gnueabihf 

    libc6-dev-armhf-cross 

    && rm -rf 

    /var/lib/apt/lists/*



RUN sed 's/^deb/deb-src/' /etc/apt/sources.list > 

        /etc/apt/sources.list.d/deb-src.list 

    && dpkg --add-architecture armhf 

    && apt-get update 

    && apt-get install -y 

        libssl-dev:armhf 

        libc6-dev:armhf 

    && rm -rf 

      /var/lib/apt/lists/*



ENV USER=root

RUN curl https://sh.rustup.rs -sSf | sh -s -- -y --verbose

ENV PATH=/root/.cargo/bin:$PATH



ENV CARGO_TARGET_ARMV7_UNKNOWN_LINUX_GNUEABIHF_LINKER=arm-linux-gnueabihf-gcc 

    CC_armv7_unknown_linux_gnueabihf="/usr/bin/arm-linux-gnueabihf-gcc" 

    CXX_armv7_unknown_linux_gnueabihf="/usr/bin/arm-linux-gnueabihf-g++" 

    CROSS_COMPILE="1" 

    OPENSSL_INCLUDE_DIR="/usr/include/arm-linux-gnueabihf" 

    OPENSSL_LIB_DIR="/usr/lib/arm-linux-gnueabihf"



RUN /root/.cargo/bin/rustup target add armv7-unknown-linux-gnueabihf



RUN dpkg --add-architecture armhf && 

    apt-get update && 

    apt-get install -y libudev-dev:armhf



RUN git clone https://github.com/paritytech/parity-ethereum.git && cd parity-ethereum && 

    cargo build --target=armv7-unknown-linux-gnueabihf --release





CMD ./parity-ethereum/target/armv7-unknown-linux-gnueabihf/release/parity



EXPOSE 8080 8545 8180

ENTRYPOINT ["/build/parity/target/armv7-unknown-linux-gnueabihf/release/parity"]