Cross compile shared library for armv5te-unknown-linux-gnueabi Rust [Mindstorm Ev3dev]

Question

Parameters:

• source = x86_x64 windows 10 or x86_x64 linux (ubuntu wsl)
• target = armv5te linux
• target_type = cdylib
• target_glibc = 2.24
• language = rust
• build_tool = cargo
• compiler = rustc

(The target is a Lego Mindstorm running a linux image from Ev3dev)

Cargo Configuration:

[package]
name = "ev3"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
jni = "0.19"
ev3dev-lang-rust = { version = "0.12.1", features=["screen"]}
jni_proc_macro= {path= "./jni_proc_macro"}

[lib]
crate-type= ["cdylib"]

[workspace]
members= ["jni_proc_macro"]

Build Configuration:

[build]
target = "armv5te-unknown-linux-gnueabi"

[target.armv5te-unknown-linux-gnueabi]
linker = "rust-lld"

Build Error:

error: linking with `rust-lld` failed: exit code: 1
  |
  = note: {...}
= note:   rust-lld: error: unable to find library -lgcc_s
          rust-lld: error: unable to find library -lutil
          rust-lld: error: unable to find library -lrt
          rust-lld: error: unable to find library -lpthread
          rust-lld: error: unable to find library -lm
          rust-lld: error: unable to find library -ldl
          rust-lld: error: unable to find library -lc


error: could not compile `ev3` due to previous error

As the error suggests the linker is missing libraries. I found no clear solution where I can download and or provide these dependencies.

My question is, A is there a diffrent way to build this successfully or B how do I solve these dependencies.

The result needs to be a shared library (.so) for linux and armv5te

Answer 1

Requirements

• wsl or linux installed
• cargo and rustc installed

(everthing is done in wsl/linux)

Prep/Build

Install cross on cargo

cargo install cross --git https://github.com/cross-rs/cross

Install docker
Clone the cross repository
Navigate into the docker folder
Create a new file with the name "Dockerfile.armv5te-unknown-linux-gnueabi-cross"
Paste this in the new file:

FROM ubuntu:16.04
ARG DEBIAN_FRONTEND=noninteractive

COPY common.sh lib.sh /
RUN /common.sh

COPY cmake.sh /
RUN /cmake.sh

COPY xargo.sh /
RUN /xargo.sh

RUN apt-get update && apt-get install --assume-yes --no-install-recommends \
    g++-arm-linux-gnueabi \
    crossbuild-essential-armel \
    libc6-dev-armel-cross

COPY deny-debian-packages.sh /
RUN TARGET_ARCH=armel /deny-debian-packages.sh \
    binutils \
    binutils-arm-linux-gnueabi

# Qemu is disabled since we've changed the scripts to require newer Python versions.
#COPY qemu.sh /
#RUN /qemu.sh arm

COPY qemu-runner base-runner.sh /

ENV CROSS_TOOLCHAIN_PREFIX=arm-linux-gnueabi-
ENV CROSS_SYSROOT=/usr/arm-linux-gnueabi
ENV CARGO_TARGET_ARMV5TE_UNKNOWN_LINUX_GNUEABI_LINKER="$CROSS_TOOLCHAIN_PREFIX"gcc \
    CARGO_TARGET_ARMV5TE_UNKNOWN_LINUX_GNUEABI_RUNNER="/qemu-runner arm" \
    AR_armv5te_unknown_linux_gnueabi="$CROSS_TOOLCHAIN_PREFIX"ar \
    CC_armv5te_unknown_linux_gnueabi="$CROSS_TOOLCHAIN_PREFIX"gcc \
    CXX_armv5te_unknown_linux_gnueabi="$CROSS_TOOLCHAIN_PREFIX"g++ \
    BINDGEN_EXTRA_CLANG_ARGS_armv5te_unknown_linux_gnueabi="--sysroot=$CROSS_SYSROOT" \
    QEMU_LD_PREFIX="$CROSS_SYSROOT" \
    RUST_TEST_THREADS=1 \
    PKG_CONFIG_PATH="/usr/lib/arm-linux-gnueabi/pkgconfig/:${PKG_CONFIG_PATH}"

Make sure the project uses "LF" newlines. if not this fixes it.
Compile the custom cross/docker build using the following command in the root of the cloned repository:

cargo build-docker-image armv5te-unknown-linux-gnueabi-cross

This will create a new docker image that will be used to compile the rust code.
Then navigate to your target project folder and run:

export CROSS_TARGET_ARMV5TE_UNKNOWN_LINUX_GNUEABI_IMAGE=ghcr.io/cross-rs/armv5te-unknown-linux-gnueabi-cross:local

(Do not close this terminal)
Now add the following to the Cargo.toml file:

[package.metadata.cross.build]
default-target = "armv5te-unknown-linux-gnueabi"

now you can run:

cross build 

Many cargo options like "--release" can be used (for more info have a look at cross in the credits)

Credits

• MeetTitan(Stackoverflow) who recomended me to use cross
• Cross project(GitHub) which powers the whole solution
• Custom cross version discussion(Cross Github)
• Alexhuszagh(Cross Github) who showed me how to build a custom cross version
• Emilgardis(Cross Github) who explained the newline bug