retroarch-cross-compile

Container image configurations to enable cross-compilation of retroarch and libretro cores, where host is a generic x86-64 machine, and target is something else. Currently, armhf target is available.

armhf

Image that can compile Retroarch and libretro cores for ARM hardfloat platforms. Tested with armv7. A snapshot of compiled cores can be found at: https://zoltanvb.github.io/armv7-hf-neon/

Building the image

cd armhf
docker build .
Note that build process will take a while (up to one hour), as it will include building a complete toolchain with crosstools-ng.

Update for 2023-09: some packages have disappeared from xenial repositories, so libmpv and libsdl2 is now excluded from building.

Using the image to build retroarch / cores

Clone the repository to build (RetroArch, individual core, or even libretro-super), then:
sudo docker run --rm -it -v "<cloned dir>:/build" <image name>
cd /build
Anything that you put under /build, will be preserved after you exit the container, others will be permanently lost.

Building RetroArch

./configure --host=arm-linux-gnueabihf
make -j <CPU count of your builder machine>
Note that there is no sense in doing "make install" inside the container. You will have the binary, but you can't execute it on your x86_64 host. But you can transfer the resulting binary to your ARM system, and run it there.

Building cores with libretro-super

export JOBS=<CPU count of your builder machine>
export platform=linux-armv7-neon
./libretro-fetch.sh <core name>
./libretro-build.sh <core name>
Note that this will produce a binary .so compiled with platform=unix-armv7-hardfloat-neon. Compiled library will be copied to dist/unix.

Building individual cores (or anything else)

There are two sets of environment variables set up in the image. The default is the toolchain installed from Ubuntu:

CC=/usr/bin/arm-linux-gnueabihf-gcc
AR=/usr/bin/arm-linux-gnueabihf-gcc-ar
CXX=/usr/bin/arm-linux-gnueabihf-g++
PKG_CONFIG_PATH=/usr/lib/arm-linux-gnueabihf/pkgconfig/

The other one is the toolchain built by crosstools-ng, extended with libs of the default toolchain:

CXX17="/opt/x-tools/arm-linux-gnueabihf/bin/arm-linux-gnueabihf-g++ -idirafter /usr/include -L/usr/lib/arm-linux-gnueabihf/"
CC17="/opt/x-tools/arm-linux-gnueabihf/bin/arm-linux-gnueabihf-gcc -idirafter /usr/include -L/usr/lib/arm-linux-gnueabihf/"
AR17=/opt/x-tools/arm-linux-gnueabihf/bin/arm-linux-gnueabihf-gcc-ar

It is highly dependent on the build system, whether cross compilation will be possible, and if so, what platform / arch / target values need to be used. Libretro cores usually honor values of CC/CXX, so to use the newer compiler, try CC=$(CC17) CXX=$(CXX17) make platform=unix-armv7. But there is no guarantee that build system will recognize this target correctly, you need to read the makefile.

More details

The reason why the build is based on such an old Ubuntu release is to avoid any library dependency problem when using the compiled images. The libretro base image can probably be substituted with a clean build from xenial as well, but it speeds up the build process.

The image has the Linaro gcc5 by default, and gcc9.4 compiled as extra. Default architecture for the compilers:

root@c17ce0b175c6:~# echo | $CC -v -E - 2>&1 | grep cc1
 /usr/lib/gcc-cross/arm-linux-gnueabihf/5/cc1 -E -quiet -v -imultiarch arm-linux-gnueabihf - -march=armv7-a -mfloat-abi=hard -mfpu=vfpv3-d16 -mthumb -mtls-dialect=gnu -fstack-protector-strong -Wformat -Wformat-security
root@c17ce0b175c6:~# echo | $CC17 -v -E - 2>&1 | grep cc1
 /opt/x-tools/arm-linux-gnueabihf/libexec/gcc/arm-linux-gnueabihf/9.4.0/cc1 -E -quiet -v -idirafter /usr/include - -mcpu=arm10e -mfloat-abi=hard -mtls-dialect=gnu -marm -march=armv5te+fp

The gcc9 setup tries to mimic the environment used for gcc5, to avoid any compatibility problems. However, it contains less fixed elements, in particular architecture can go lower than the armv7-a default of gcc5. Usage of neon is not hardcoded anywhere, except for the target name in libretro-super (which, in turn, may cause the makefile to enable it).

Caveats

• gcc is present, but it produces x86_64 code, if this happens, makefile has redefined CC/CXX. Use readelf -h on the produced binary to check.
• hardfloat is coming from compiler (both compilers)
• compiling for armv6 is theoretically supported but needs to be tested (see https://stackoverflow.com/questions/35132319/build-for-armv6-with-gnueabihf/51201725#51201725)
• cmake is present but wasn't tested in detail
• image does not contain any particular HW library like libbrcmEGL for Raspberry Pi. so it will not be able to link against that. This may mean a severe performance hit for any core that uses OpenGL (or Retroarch itself), depending on OS. See https://forums.raspberrypi.com/viewtopic.php?t=317511 for some RPi specifics.
• image is for Unix/Linux target. Does not contain any Android or iOS tools.