Cross-compilation allows you to build software for one architecture on another. In our case, we'd like to build for ARM from x86, to facilitate continuous integration (jenkins). This supports testing and release engineering.
To cross-compile, you need a few things. You need:
- Cross-aware toolchain. In our case, golang supports cross-compilation
out-of-the-box. Our use of
cgohowever requires that a C/C++ cross-aware toolchain is also available. - A "sysroot". This is a filesystem image of the root of a system. In some cases, go needs to use a C compiler, and in turn a sysroot is required. To get a sysroot, you need to build one.
The toolchain should be installed on build machines by default; if the tools are not available, the build will complain and fail. The sysroot is built automatically and stored in the cloud; it will be downloaded and used as required.
An output product of the OpenWrt build is a root filesystem tree, which is
suitable for use as a sysroot. The cross-compiling C/C++ toolchain (for
arm-openwrt-gnueabi) is also an output product of the full OpenWrt build.
Instructions for building the Brightgate OpenWrt distribution are given in the README.md for the rWRT repository.
$ sudo apt-get install multistrap
$ cd build/cross-compile
$ ./build-multistrap-sysroot.sh raspbian-stretch.multistrap
...When this is done, you will have a directory called sysroot.raspbian-stretch.
You can do this in one step, from the top-level directory:
$ make build-sysrootPass the target distribution to the build via the DISTRO flag, giving the
appropriate GOARCH and GOARM flags. In addition to using the appropriate
sysroot, the target distro is used to build the appropriate packages.
For the OpenWrt build, use 'openwrt' as the distro:
$ make DISTRO=openwrt GOARCH=arm GOARM=7 packagesFor Raspbian, use 'debian' as the distro:
$ make DISTRO=debian GOARCH=arm GOARM=7 packages- Investigate https://github.com/karalabe/xgo
- Set GOARM? Needs research.