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Cross Compilation for ARM on Windows

Building ARM for Windows can be done using cross compilation.


Install the ARM tools and Windows SDK, as described here.

Cross compiling CoreCLR

Build using "-arm" as the architecture. For example:

C:\coreclr> build.cmd -arm -debug

Cross Compilation for ARM, ARM64 or x86 on Linux

Through cross compilation, on Linux it is possible to build CoreCLR for arm or arm64.

Requirements for targetting Debian based distros

You need a Debian based host and the following packages need to be installed:

ben@ubuntu ~/git/coreclr/ $ sudo apt-get install qemu qemu-user-static binfmt-support debootstrap

In addition, to cross compile CoreCLR the binutils for the target are required. So for arm you need:

ben@ubuntu ~/git/coreclr/ $ sudo apt-get install binutils-arm-linux-gnueabihf

and conversely for arm64:

ben@ubuntu ~/git/coreclr/ $ sudo apt-get install binutils-aarch64-linux-gnu

Requirements for targetting ARM or ARM64 Alpine Linux

You can use any Linux distro as a host. The qemu, qemu-user-static and binfmt-support packages need to be installed (the names may be different for some distros).

In addition, to cross compile CoreCLR, the binutils for Alpine need to be built from the repo, since they are not available as packages.

To build them, use the following steps:

  • Clone the repo
  • Create a new config.mak file in the root directory of the repo and add the following lines into it:
    • TARGET = armv6-alpine-linux-musleabihf for ARM or TARGET = aarch64-alpine-linux-musl for ARM64
    • OUTPUT = /usr
    • BINUTILS_CONFIG=--enable-gold=yes
  • Run make with current directory set to the root of the repo
  • Run sudo make install

Generating the rootfs

The cross\ script can be used to download the files needed for cross compilation. It will generate a rootfs as this is what CoreCLR targets.

Usage: ./cross/ [BuildArch] [LinuxCodeName] [lldbx.y] [--skipunmount]
BuildArch can be: arm(default), armel, arm64, x86
LinuxCodeName - optional, Code name for Linux, can be: trusty(default), vivid, wily, xenial or alpine. If BuildArch is armel, LinuxCodeName is jessie(default) or tizen.
lldbx.y - optional, LLDB version, can be: lldb3.6(default), lldb3.8. This is ignored when building rootfs for Alpine Linux.

The 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:

ben@ubuntu ~/git/coreclr/ $ sudo ./cross/ arm

You can choose Linux code name to match your target, give vivid for Ubuntu 15.04, wily for Ubuntu 15.10. The default is trusty, version Ubuntu 14.04.

ben@ubuntu ~/git/coreclr/ $ sudo ./cross/ arm wily

and if you wanted to generate the rootfs elsewhere:

ben@ubuntu ~/git/coreclr/ $ sudo ROOTFS_DIR=/home/ben/coreclr-cross/arm ./cross/ arm

For example, to generate an armel rootfs:

hqu@ubuntu ~/git/coreclr/ $ sudo ./cross/ armel

You can choose code name to match your target, give jessie for Debian, tizen for Tizen. The default is jessie.

hque@ubuntu ~/git/coreclr/ $ sudo ./cross/ armel tizen

and if you wanted to generate the rootfs elsewhere:

hque@ubuntu ~/git/coreclr/ $ sudo ROOTFS_DIR=/home/ben/coreclr-cross/armel ./cross/ armel tizen

Cross compiling CoreCLR

Once the rootfs has been generated, it will be possible to cross compile CoreCLR. If ROOTFS_DIR was set when generating the rootfs, then it must also be set when running

So, without ROOTFS_DIR:

ben@ubuntu ~/git/coreclr/ $ ./ arm debug verbose cross

And with:

ben@ubuntu ~/git/coreclr/ $ ROOTFS_DIR=/home/ben/coreclr-cross/arm ./ arm debug verbose cross

As usual, the resulting binaries will be found in bin/Product/BuildOS.BuildArch.BuildType/

Compiling System.Private.CoreLib for ARM Linux

It is also possible to use a Windows and a Linux machine to build the managed components of CoreCLR for ARM Linux. This can be useful when the build on the target platform fails, for example due to Mono issues.

Build System.Private.CoreLib on Windows

The following instructions assume you are on a Windows machine with a clone of the CoreCLR repo that has a correctly configured environment.

To build System.Private.CoreLib for Linux, run the following command:

D:\git\coreclr> build.cmd linuxmscorlib arm

The arguments freebsdmscorlib and osxmscorlib can be used instead to build System.Private.CoreLib for FreeBSD or OS X.

The output is at bin\Product<BuildOS>.arm.Debug\System.Private.CoreLib.dll.

Build System.Private.CoreLib on Ubuntu

The following instructions assume you are on a Linux machine such as Ubuntu 14.04 x86 64bit.

To build System.Private.CoreLib for Linux, run the following command:

    lgs@ubuntu ~/git/coreclr/ $ arm debug verbose

The output is at bin/Product/.arm.Debug/System.Private.CoreLib.dll.

    lgs@ubuntu ~/git/coreclr/ $ file ./bin/Product/Linux.arm.Debug/System.Private.CoreLib.dll 
    ./bin/Product/Linux.arm.Debug/System.Private.CoreLib.dll: PE32 executable (DLL) 
    (console) ARMv7 Thumb Mono/.Net assembly, for MS Windows

Building coreclr for Linux ARM Emulator

It is possible to build coreclr binaries (native and System.Private.CoreLib.dll) and run coreclr unit tests on the Linux ARM Emulator (latest version provided here: #3805). The tests/scripts/ 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.ext4 exists)
    The emulator rootfs is of 4GB size by default. But to enable testing of coreclr binaries on the emulator, you need to resize the rootfs (to atleast 7GB) using the instructions given in the doc/RESIZE-IMAGE.txt file of the extracted emulator.
  • 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 libcoreclr and System.Private.CoreLib for the Linux ARM Emulator, run the following command:

prajwal@ubuntu ~/coreclr $ ./tests/scripts/ \
    --emulatorPath=/opt/linux-arm-emulator \
    --mountPath=/opt/linux-arm-emulator-root \
    --buildConfig=Release \

The Linux ARM Emulator is based on soft floating point and thus the native binaries in coreclr are built for the armel architecture. The coreclr binaries generated by the above command (native and System.Private.CoreLib) can be found at ~/coreclr/bin/Product/Linux.armel.Release.

To build libcoreclr and System.Private.CoreLib, and run selected coreclr unit tests on the emulator, do the following:

  • Download the latest Coreclr unit test binaries (or build on Windows) from here: Debug and Release.
    Setup the binaries at ~/coreclr/bin/tests/Windows_NT.x64.Release.
  • Build corefx binaries for the Emulator as given here.
    Setup these binaries at ~/corefx/bin/Linux.arm-softfp.Release, ~/corefx/bin/Linux.AnyCPU.Release, ~/corefx/bin/Unix.AnyCPU.Release, and ~/corefx/bin/AnyOS.AnyCPU.Release.
  • Run the following command (change value of --testDirFile argument to the file containing your selection of tests):
prajwal@ubuntu ~/coreclr $ ./tests/scripts/ \
    --emulatorPath=/opt/linux-arm-emulator \
    --mountPath=/opt/linux-arm-emulator-root \
    --buildConfig=Release \
    --testRootDir=~/coreclr/bin/tests/Windows_NT.x64.Release \
    --coreFxNativeBinDir=~/corefx/bin/Linux.arm-softfp.Release \
    --coreFxBinDir="~/corefx/bin/Linux.AnyCPU.Release;~/corefx/bin/Unix.AnyCPU.Release;~/corefx/bin/AnyOS.AnyCPU.Release" \