trouble cross compiling for a raspberry pi

[ryepup]

I'm getting some novice cross-compiling errors that I'm not sure how to resolve. I think I don't have libudev-dev setup right, but I'm unsure how to get them in the right place.

libudev-sys is a transitive dependency of a program I'm trying to compile on my ubuntu laptop and copy a binary over to the pi.

My build script:

#!/bin/sh

SYSROOT=/build/root

export PKG_CONFIG_DIR=
export PKG_CONFIG_LIBDIR=${SYSROOT}/usr/lib/pkgconfig:${SYSROOT}/usr/share/pkgconfig
export PKG_CONFIG_SYSROOT_DIR=${SYSROOT}
export PKG_CONFIG_ALLOW_CROSS=1

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

A sample run:

$ ./build.sh
   Compiling libc v0.2.82
   Compiling pkg-config v0.3.19
   Compiling void v1.0.2
   Compiling slab v0.4.2
   Compiling nix v0.14.1
   Compiling nix v0.17.0
   Compiling pin-project-lite v0.1.11
   Compiling bytes v0.5.6
   Compiling futures-core v0.3.13
   Compiling futures-sink v0.3.13
   Compiling pin-utils v0.1.0
   Compiling pin-project-lite v0.2.4
   Compiling futures-task v0.3.13
   Compiling futures-util v0.3.13
   Compiling libudev-sys v0.1.4
error: failed to run custom build command for `libudev-sys v0.1.4`

Caused by:
  process didn't exit successfully: `/home/.../target/release/build/libudev-sys-dac8bee601eaad20/build-script-build` (exit code: 101)
  --- stdout
  cargo:rerun-if-env-changed=LIBUDEV_NO_PKG_CONFIG
  cargo:rerun-if-env-changed=PKG_CONFIG_ALLOW_CROSS_armv7-unknown-linux-gnueabihf
  cargo:rerun-if-env-changed=PKG_CONFIG_ALLOW_CROSS_armv7_unknown_linux_gnueabihf
  cargo:rerun-if-env-changed=TARGET_PKG_CONFIG_ALLOW_CROSS
  cargo:rerun-if-env-changed=PKG_CONFIG_ALLOW_CROSS
  cargo:rerun-if-env-changed=PKG_CONFIG
  cargo:rerun-if-env-changed=LIBUDEV_STATIC
  cargo:rerun-if-env-changed=LIBUDEV_DYNAMIC
  cargo:rerun-if-env-changed=PKG_CONFIG_ALL_STATIC
  cargo:rerun-if-env-changed=PKG_CONFIG_ALL_DYNAMIC
  cargo:rerun-if-env-changed=PKG_CONFIG_PATH_armv7-unknown-linux-gnueabihf
  cargo:rerun-if-env-changed=PKG_CONFIG_PATH_armv7_unknown_linux_gnueabihf
  cargo:rerun-if-env-changed=TARGET_PKG_CONFIG_PATH
  cargo:rerun-if-env-changed=PKG_CONFIG_PATH
  cargo:rerun-if-env-changed=PKG_CONFIG_LIBDIR_armv7-unknown-linux-gnueabihf
  cargo:rerun-if-env-changed=PKG_CONFIG_LIBDIR_armv7_unknown_linux_gnueabihf
  cargo:rerun-if-env-changed=TARGET_PKG_CONFIG_LIBDIR
  cargo:rerun-if-env-changed=PKG_CONFIG_LIBDIR
  cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR_armv7-unknown-linux-gnueabihf
  cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR_armv7_unknown_linux_gnueabihf
  cargo:rerun-if-env-changed=TARGET_PKG_CONFIG_SYSROOT_DIR
  cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR

  --- stderr
  thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: "`\"pkg-config\" \"--libs\" \"--cflags\" \"libudev\"` did not exit successfully: exit code: 1\n--- stderr\nPackage libudev was not found in the pkg-config search path.\nPerhaps you should add the directory containing `libudev.pc\'\nto the PKG_CONFIG_PATH environment variable\nNo package \'libudev\' found\n"', /home/.../.cargo/registry/src/github.1485827954.workers.dev-1ecc6299db9ec823/libudev-sys-0.1.4/build.rs:38:41
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
warning: build failed, waiting for other jobs to finish...
error: build failed

I'm getting some clear advice, but I don't know how to follow it:

Package libudev was not found in the pkg-config search path.
Perhaps you should add the directory containing `libudev.pc'
to the PKG_CONFIG_PATH environment variable

I've run a apt install libudev-dev to get the package installed, and that provided /usr/lib/x86_64-linux-gnu/pkgconfig/libudev.pc; I don't think that's suitable for a armv7-unknown-linux-gnueabihf binary. I tried adding that x86_64 path to my PKG_CONFIG_PATH and was able to get through compilation, but failed at linking:

/usr/lib/gcc-cross/arm-linux-gnueabihf/9/../../../../arm-linux-gnueabihf/bin/ld: cannot find -ludev

Any pointers on how I could get a libudev.pc that's suitable?

[ryepup]

Ok, after more googling and guess-and-check I think I figured it out. The missing piece was getting my laptop configured to install packages for other architectures, found on Ask Ubuntu: Cross-compile for armhf and install a static library.

This is what worked for me:

• update my /etc/apt/sources.list to add a [arch=amd64] to the existing sources, and add new sources to pull armhf packages from ports.ubuntu.com

    # deb cdrom:[Ubuntu 20.04 LTS _Focal Fossa_ - Release amd64 (20200423)]/ focal main restricted
    deb [arch=amd64] http://archive.ubuntu.com/ubuntu/ focal main restricted universe multiverse
    deb [arch=amd64] http://security.ubuntu.com/ubuntu/ focal-security main restricted universe multiverse
    deb [arch=amd64] http://archive.ubuntu.com/ubuntu/ focal-updates main restricted universe multiverse
    # added these two:
    deb [arch=armhf] http://ports.ubuntu.com/ubuntu-ports focal main universe
    deb [arch=armhf] http://ports.ubuntu.com/ubuntu-ports focal-updates main universe
  

• update packages so all these changes take effect: sudo apt update

• let dpkg know I'm interested in more architectures

    sudo dpkg --add-architecture armhf
  

• install the libudev headers for armhf: sudo apt install libudev-dev:armhf - this wanted a bunch of related packages and I said yes

• install a compiler capable of generating armhf code: sudo apt install gcc-arm-linux-gnueabihf

• add some more environment variables in my build script:

#!/bin/sh

SYSROOT=/build/root

export PKG_CONFIG_DIR=
export PKG_CONFIG_LIBDIR=${SYSROOT}/usr/lib/pkgconfig:${SYSROOT}/usr/share/pkgconfig
export PKG_CONFIG_SYSROOT_DIR=${SYSROOT}
export PKG_CONFIG_ALLOW_CROSS=1
# tell pkg-config where to find libudev.pc
export PKG_CONFIG_PATH=/usr/lib/arm-linux-gnueabihf/pkgconfig
# tell cargo to link with an armhf compatible linker
export CARGO_TARGET_ARMV7_UNKNOWN_LINUX_GNUEABIHF_LINKER=arm-linux-gnueabihf-gcc

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

Do you think any of this should end up in the README here? I'd be happy to submit a PR, but unsure what level of detail would be useful.

[zhang-ray]

I got the similar error message in rust docker container:

error: failed to run custom build command for `libudev-sys v0.1.4`
Caused by:
  process didn't exit successfully: `/builds/zhangruihuai/playground-rust/tci-linux/target/debug/build/libudev-sys-d387404a27cfd86d/build-script-build` (exit status: 101)
  --- stdout
  cargo:rerun-if-env-changed=LIBUDEV_NO_PKG_CONFIG
  cargo:rerun-if-env-changed=PKG_CONFIG_x86_64-unknown-linux-gnu
  cargo:rerun-if-env-changed=PKG_CONFIG_x86_64_unknown_linux_gnu
  cargo:rerun-if-env-changed=HOST_PKG_CONFIG
  cargo:rerun-if-env-changed=PKG_CONFIG
  cargo:rerun-if-env-changed=LIBUDEV_STATIC
  cargo:rerun-if-env-changed=LIBUDEV_DYNAMIC
  cargo:rerun-if-env-changed=PKG_CONFIG_ALL_STATIC
  cargo:rerun-if-env-changed=PKG_CONFIG_ALL_DYNAMIC
  cargo:rerun-if-env-changed=PKG_CONFIG_PATH_x86_64-unknown-linux-gnu
  cargo:rerun-if-env-changed=PKG_CONFIG_PATH_x86_64_unknown_linux_gnu
  cargo:rerun-if-env-changed=HOST_PKG_CONFIG_PATH
  cargo:rerun-if-env-changed=PKG_CONFIG_PATH
  cargo:rerun-if-env-changed=PKG_CONFIG_LIBDIR_x86_64-unknown-linux-gnu
  cargo:rerun-if-env-changed=PKG_CONFIG_LIBDIR_x86_64_unknown_linux_gnu
  cargo:rerun-if-env-changed=HOST_PKG_CONFIG_LIBDIR
  cargo:rerun-if-env-changed=PKG_CONFIG_LIBDIR
  cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR_x86_64-unknown-linux-gnu
  cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR_x86_64_unknown_linux_gnu
  cargo:rerun-if-env-changed=HOST_PKG_CONFIG_SYSROOT_DIR
  cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR
  --- stderr
  thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: "`\"pkg-config\" \"--libs\" \"--cflags\" \"libudev\"` did not exit successfully: exit status: 1\nerror: could not find system library 'libudev' required by the 'libudev-sys' crate\n\n--- stderr\nPackage libudev was not found in the pkg-config search path.\nPerhaps you should add the directory containing `libudev.pc'\nto the PKG_CONFIG_PATH environment variable\nNo package 'libudev' found\n"', /usr/local/cargo/registry/src/github.1485827954.workers.dev-1ecc6299db9ec823/libudev-sys-0.1.4/build.rs:38:41
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
warning: build failed, waiting for other jobs to finish...
ERROR: Job failed: exit code 1