dockcross/CONTRIBUTING.md

Contributing

Getting started

How to add a new image ? (With crosstool-ng)

In this part, we will see how to add a new image, we will take example with linux-arm64 for a raspberry pi 4, with crosstool-ng.

Build and config crosstool-ng

To start, you need to download the source code of crosstool-ng:

git clone --recurse-submodules --remote-submodules https://github.com/crosstool-ng/crosstool-ng.git

Go to crosstool-ng folder:

cd crosstool-ng

Change git branch:

git checkout crosstool-ng-1.25.0

Once in the crosstool-ng folder, you must first run the bootstrap script:

./bootstrap

Then run the configure script:

Note: -enable-local does a portable install of crosstool-ng.:

./configure --enable-local

Finally, launch the building of crosstool-ng:

make -j$(nproc)

Once the crosstool-ng build is complete, you can run this command to test crosstool-ng:

./ct-ng --version

Before starting the configuration of the toolchains, i recommend you to use one of the examples from crosstool-ng and then make your changes, the command to display the examples:

./ct-ng list-samples

We will take the example of aarch64-rpi4-linux-gnu, a .config file will be created:

./ct-ng aarch64-rpi4-linux-gnu

Alternatively, we could copy an existing crosstool-ng.config from one of the target folders in the dockcross project to the local .config:

cp path/to/dockcross/linux-arm64 .config

We will configure the toolchains according to our needs:

./ct-ng menuconfig

Once the modifications are made, we will display the name of the toolchains, it will be useful later:

./ct-ng show-tuple

Configuring docker image

You must create a file with the same name of the docker image (linux-arm64).

Copy the .config of crosstool-ng to this file (linux-arm64) and rename it to crosstool-ng.config.

You need to create a file named Toolchain.cmake in linux-arm64.

Copy text to Toolchain.cmake file:

set(CMAKE_SYSTEM_NAME Linux)
set(CMAKE_SYSTEM_VERSION 1)
set(CMAKE_SYSTEM_PROCESSOR ARM64)

set(cross_triple $ENV{CROSS_TRIPLE})
set(cross_root $ENV{CROSS_ROOT})

set(CMAKE_C_COMPILER $ENV{CC})
set(CMAKE_CXX_COMPILER $ENV{CXX})
set(CMAKE_Fortran_COMPILER $ENV{FC})

set(CMAKE_CXX_FLAGS "-I ${cross_root}/include/")

set(CMAKE_FIND_ROOT_PATH ${cross_root} ${cross_root}/${cross_triple})
set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY BOTH)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE BOTH)
set(CMAKE_SYSROOT ${cross_root}/${cross_triple}/sysroot)

set(CMAKE_CROSSCOMPILING_EMULATOR /usr/bin/qemu-arm64)

Then ou must change these lines according to the targeted architecture, here ARM64:

set(CMAKE_SYSTEM_PROCESSOR ARM64)
set(CMAKE_CROSSCOMPILING_EMULATOR /usr/bin/qemu-arm64)

Then you must create a file named Dockerfile.in in the image folder (linux-arm64).

Copy text to Dockerfile.in file:

FROM dockcross/base:latest

LABEL maintainer="Matt McCormick matt.mccormick@kitware.com"

# This is for 64-bit ARM Linux machine

# Crosstool-ng crosstool-ng-1.25.0 2022-05-13
ENV CT_VERSION crosstool-ng-1.25.0

#include "common.crosstool"

# The cross-compiling emulator
RUN apt-get update \
&& apt-get install -y \
  qemu-user \
  qemu-user-static \
&& apt-get clean --yes

# The CROSS_TRIPLE is a configured alias of the "aarch64-unknown-linux-gnu" target.
ENV CROSS_TRIPLE aarch64-unknown-linux-gnu

ENV CROSS_ROOT ${XCC_PREFIX}/${CROSS_TRIPLE}
ENV AS=${CROSS_ROOT}/bin/${CROSS_TRIPLE}-as \
    AR=${CROSS_ROOT}/bin/${CROSS_TRIPLE}-ar \
    CC=${CROSS_ROOT}/bin/${CROSS_TRIPLE}-gcc \
    CPP=${CROSS_ROOT}/bin/${CROSS_TRIPLE}-cpp \
    CXX=${CROSS_ROOT}/bin/${CROSS_TRIPLE}-g++ \
    LD=${CROSS_ROOT}/bin/${CROSS_TRIPLE}-ld \
    FC=${CROSS_ROOT}/bin/${CROSS_TRIPLE}-gfortran

ENV QEMU_LD_PREFIX "${CROSS_ROOT}/${CROSS_TRIPLE}/sysroot"
ENV QEMU_SET_ENV "LD_LIBRARY_PATH=${CROSS_ROOT}/lib:${QEMU_LD_PREFIX}"

COPY Toolchain.cmake ${CROSS_ROOT}/
ENV CMAKE_TOOLCHAIN_FILE ${CROSS_ROOT}/Toolchain.cmake

ENV PKG_CONFIG_PATH /usr/lib/aarch64-linux-gnu/pkgconfig

# Linux kernel cross compilation variables
ENV PATH ${PATH}:${CROSS_ROOT}/bin
ENV CROSS_COMPILE ${CROSS_TRIPLE}-
ENV ARCH arm64

#include "common.label-and-env"

Then ou must change these lines according to the targeted architecture.

Here you have to change the value according to the name of the toolchain (./ct-ng show-tuple):

ENV CROSS_TRIPLE aarch64-unknown-linux-gnu

These lines also need to be changed:

LABEL maintainer="Matt McCormick matt.mccormick@kitware.com"
ENV PKG_CONFIG_PATH /usr/lib/aarch64-linux-gnu/pkgconfig
ENV ARCH arm64

Once this part is finished, there must be 3 files in the linux-arm64 folder:

• crosstool-ng.config, the configuration of the toolchain/crosstool-ng.
• Dockerfile.in, the docker file.
• Toolchain.cmake, the CMake file for the toolchains.

Makefile

For this last part, we will see how to add the image to the Makefile and to a github action.

You need to add the image/folder name (linux-arm64) to the STANDARD_IMAGES variable in the Makefile:

# These images are built using the "build implicit rule"
STANDARD_IMAGES = android-arm android-arm64 android-x86 android-x86_64 \
 linux-x86 linux-x64 linux-x64-clang linux-arm64 linux-arm64-musl linux-arm64-full \
 linux-armv5 linux-armv5-musl linux-armv5-uclibc linux-m68k-uclibc linux-s390x linux-x64-tinycc \
 linux-armv6 linux-armv6-lts linux-armv6-musl linux-arm64-lts \
 linux-armv7l-musl linux-armv7 linux-armv7a linux-armv7-lts linux-x86_64-full \
 linux-mips linux-ppc64le linux-riscv64 linux-riscv32 linux-xtensa-uclibc \
 web-wasi \
 windows-static-x86 windows-static-x64 windows-static-x64-posix windows-armv7 \
 windows-shared-x86 windows-shared-x64 windows-shared-x64-posix windows-arm64

You need to add the image/folder name (linux-arm64) to the GEN_IMAGES variable in the Makefile:

# Generated Dockerfiles.
GEN_IMAGES = android-arm android-arm64 \
 linux-x86 linux-x64 linux-x64-clang linux-arm64 linux-arm64-musl linux-arm64-full \
 manylinux2014-x64 manylinux2014-x86 \
 manylinux2014-aarch64 linux-arm64-lts \
 web-wasm web-wasi linux-mips windows-arm64 windows-armv7 \
 windows-static-x86 windows-static-x64 windows-static-x64-posix \
 windows-shared-x86 windows-shared-x64 windows-shared-x64-posix \
 linux-armv7 linux-armv7a linux-armv7l-musl linux-armv7-lts linux-x86_64-full \
 linux-armv6 linux-armv6-lts linux-armv6-musl \
 linux-armv5 linux-armv5-musl linux-armv5-uclibc linux-ppc64le linux-s390x \
 linux-riscv64 linux-riscv32 linux-m68k-uclibc linux-x64-tinycc linux-xtensa-uclibc

Image building and testing

You can now start building the image:

make linux-arm64

When finished, you can test it:

make linux-arm64.test

If you want to go a little further in the tests:

docker run --rm linux-arm64 > ./linux-arm64
chmod +x ./linux-arm64

And then run the commands to build a project (you must be in the directory of your project to build):

./linux-arm64 make

With CMake + Ninja:

./linux-arm64 cmake -Bbuild -S. -GNinja
./linux-arm64 ninja -Cbuild

CI (github action)

To finish, you have to add to .github/workflows/main.yml the image/folder name:

          # Linux arm64/armv8 images
          - {
              image: "linux-arm64",
              stockfish: "yes",
              stockfish_arg: "ARCH=armv8",
              ninja: "yes",
              ninja_arg: "",
              openssl: "yes",
              openssl_arg: "linux-aarch64",
              C: "yes",
              C_arg: "",
              C-Plus-Plus: "yes",
              C-Plus-Plus_arg: "",
              fmt: "yes",
              fmt_arg: "",
              cpython: "yes",
              cpython_arg: "--host=aarch64-unknown-linux-gnu --target=aarch64-unknown-linux-gnu",
            }

You can disable and enable the build of certain tests which can cause problems with certain CPU architectures (eg. OpenSSL with Risc-V...).