Supports RasPi OS based on debian:bullseye with RasPi Zero / Zero W machine, though probably can be modified for other configurations. The default GCC version is 10.2.
Check version of your binutils and compiler with
ld -v
gcc -v
Set the versions with docker environment variables BINUTILS_VERSION and GCC_VERSION, but note that some of them may not exist on ftp server, so try to fit at least Major and Minor versions.
Build the docker image
docker build -t nyacpp/raspi_cross_gcc .
The build time depends on your PC, but should be around 15 minutes.
Make sure gcc is installed on RasPi:
sudo apt install g++
Then on your PC, copy libraries from RasPi:
rsync -rlu --del --copy-unsafe-links --info=progress2 pi@<rpi>:/{lib,usr} ~/raspi
It takes around half an hour for clean system.
Build test application in the docker:
docker run -it --rm \
-v $PWD/test:/home/pi/test \
-v ~/raspi:/raspi \
-v ~/raspi/usr/lib/gcc:/cross/lib/gcc \
nyacpp/raspi_cross_gcc \
make -C test
Then you can check the resulting file:
file test/build/a
The gcc/g++ cross-compiler can be used to speed up build significantly (e.g. hours instead of days).
The default gcc-arm-linux-gnueabihf package is not suitable, because it targets ARMv7 cpu, while RasPi Zero is ARMv6.
Also even though both are hf (hard float operations), the RasPi Zero cpu is VFP2, while ARMv7 is VFP3 (Vector Floating Point).
The build of libC and gccLib is not needed, because the libraries already exist on RasPi machine, so it better to use native ones (also it's quite hard to cross compile those libraries with gcc-10).
The configuration option --prefix in Dockerfile specifies compiler installation path. The path can be changed later with gcc -B option or GCC_EXEC_PREFIX environment variable. But unfortunately it influences all paths together, like ld, .o, .so, thus probably not suitable for cross compilation.
Instead of changing prefix, the needed object files and libraries are mounted into compiler specific directory. You can notice in the test above, /cross/lib/gcc directory was mounted for this purpose.
The gcc --sysroot option is not related to the above and used to search additional stuff like crt1.o.