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Cross Compilation for ARM on Linux
It is possible to build CoreFx on Linux for arm, armel, or arm64 by cross compiling. It is very similar to the cross compilation procedure of CoreCLR.
Requirements
You need a Debian based host, and the following packages need to be installed:
lgs@ubuntu ~/git/corefx/ $ sudo apt-get install qemu qemu-user-static binfmt-support debootstrap
In addition, to cross compile CoreFX, the binutils for the target are required. So for arm you need:
lgs@ubuntu ~/git/corefx/ $ sudo apt-get install binutils-arm-linux-gnueabihf
for armel:
lgs@ubuntu ~/git/corefx/ $ sudo apt-get install binutils-arm-linux-gnueabi
and for arm64 you need:
lgs@ubuntu ~/git/corefx/ $ sudo apt-get install binutils-aarch64-linux-gnu
Generating the rootfs
The cross\build-rootfs.sh script can be used to download the files needed for cross compilation. It will generate an Ubuntu 14.04 rootfs as this is what CoreFX targets.
Usage: ./cross/build-rootfs.sh [BuildArch] [UbuntuCodeName]
BuildArch can be: arm, armel, arm64, x86
UbuntuCodeName - optional, Code name for Ubuntu, can be: trusty(default), vivid, wily, xenial. If BuildArch is armel, jessie(default) or tizen.
The build-rootfs.sh script must be run as root, as it has to make some symlinks to the system. It will, by default, generate the rootfs in cross\rootfs\<BuildArch> however this can be changed by setting the ROOTFS_DIR environment variable.
For example, to generate an arm rootfs:
lgs@ubuntu ~/git/corefx/ $ sudo ./cross/build-rootfs.sh arm
and if you wanted to generate the rootfs elsewhere:
lgs@ubuntu ~/git/corefx/ $ sudo ROOTFS_DIR=/home/lgs/corefx-cross/arm ./build-rootfs.sh arm
Cross compiling for native CoreFX
Once the rootfs has been generated, it will be possible to cross compile CoreFX. If ROOTFS_DIR was set when generating the rootfs, then it must also be set when running build.sh.
So, without ROOTFS_DIR:
lgs@ubuntu ~/git/corefx/ $ ./build-native.sh -debug -buildArch=arm -- verbose cross
And with:
lgs@ubuntu ~/git/corefx/ $ ROOTFS_DIR=/home/lgs/corefx-cross/arm ./build-native.sh -debug -buildArch=arm -- verbose cross
As usual the generated binaries will be found in bin/BuildOS.BuildArch.BuildType/native as following:
lgs@ubuntu ~/git/corefx/ ls -al ./bin/Linux.arm.Debug/native
total 988
drwxrwxr-x 2 lgs lgs 4096 3 6 18:33 .
drwxrwxr-x 3 lgs lgs 4096 3 6 18:33 ..
-rw-r--r-- 1 lgs lgs 19797 3 6 18:33 System.IO.Compression.Native.so
-rw-r--r-- 1 lgs lgs 428232 3 6 18:33 System.Native.a
-rw-r--r-- 1 lgs lgs 228279 3 6 18:33 System.Native.so
-rw-r--r-- 1 lgs lgs 53089 3 6 18:33 System.Net.Http.Native.so
-rw-r--r-- 1 lgs lgs 266720 3 6 18:33 System.Security.Cryptography.Native.so
lgs@ubuntu ~/git/corefx/ file ./bin/Linux.arm.Debug/native/System.Native.so
./bin/Linux.arm.Debug/native/System.Native.so:
ELF 32-bit LSB shared object, ARM, EABI5 version 1 (SYSV),
dynamically linked, BuildID[sha1]=fac50f1bd657c1759f0ad6cf5951511ddf252e67, not stripped
Compiling for managed CoreFX
The managed components of CoreFX are architecture-independent and thus do not require a special build for arm, armel or arm64.
Many of the managed binaries are also OS-independent, e.g. System.Linq.dll, while some are OS-specific, e.g. System.IO.FileSystem.dll, with different builds for Windows and Linux.
lgs@ubuntu ~/git/corefx/ $ ./build-managed.sh -debug -verbose
The output is at bin/[BuildConfiguration] where BuildConfiguration looks something like netcoreapp-<OSGroup>-Debug-<Architecture>. Ex: bin/netcoreapp-Linux-Debug-x64. For more details on the build configurations see project-guidelines
Building corefx for Linux ARM Emulator
It is possible to build corefx binaries (native and managed) for the Linux ARM Emulator (latest version provided here: #3805).
The scripts/arm32_ci_script.sh script does this.
The following instructions assume that:
- You have set up the extracted emulator at
/opt/linux-arm-emulator(such that/opt/linux-arm-emulator/platform/rootfs-t30.ext4exists) - The mount path for the emulator rootfs is
/opt/linux-arm-emulator-root(change this path if you have a working directory at this path).
All the following instructions are for the Release mode. Change the commands and files accordingly for the Debug mode.
To just build the native and managed corefx binaries for the Linux ARM Emulator, run the following command:
prajwal@ubuntu ~/corefx $ ./scripts/arm32_ci_script.sh \
--emulatorPath=/opt/linux-arm-emulator \
--mountPath=/opt/linux-arm-emulator-root \
--buildConfig=Release
The Linux ARM Emulator is based on the soft floating point and thus the native binaries are generated for the armel architecture. The corefx binaries generated by the above command can be found at ~/corefx/bin/Linux.armel.Release, ~/corefx/bin/Linux.AnyCPU.Release, ~/corefx/bin/Unix.AnyCPU.Release, and ~/corefx/bin/AnyOS.AnyCPU.Release.
Build corefx for a new architecture
When building for a new architecture you will need to build the native pieces separate from the managed pieces in order to correctly boot strap the native runtime. Instead of calling build.sh directly you should instead split the calls like such:
Example building for armel
build-native.sh -buildArch=armel
--> Output goes to bin/runtime/netcoreapp-Linux-Debug-armel
build-managed.sh -buildArch=x64
--> Output goes to bin/runtime/netcoreapp-Linux-Debug-x64
The reason you need to build the managed portion for x64 is because it depends on runtime packages for the new architecture which don't exist yet so we use another existing architecture such as x64 as a proxy for building the managed binaries.
Similar if you want to try and run tests you will have to copy the managed assemblies from the proxy directory (i.e. netcoreapp-Linux-Debug-x64) to the new architecture directory (i.e netcoreapp-Linux-Debug-armel) and run code via another host such as corerun because dotnet is at a higher level and most likely doesn't exist for the new architecture yet.
Once all the necessary builds are setup and packages are published the spliting of the build and manual creation of the runtime should no longer be necessary.