Add arm64 cross-build images targeting Ubuntu 16.04 (#754)

README.md

@@ -120,6 +120,8 @@ A precondition for building an image is to ensure that the base image specified
 
 In certain cases, it is necessary to run custom logic before and after the Dockerfiles are built. For example, to build the Dockerfiles that are used for cross-gen builds, the rootfs that gets copied into the Docker image needs to be built on the host OS. To support these scenarios a `pre-build` or `post-build` bash or PowerShell script can be placed in a `hooks` folder next to the Dockerfile. The scripts will get invoked by the build process.
 
+Note that multi-stage docker builds can be used to accomplish the same without build hooks, and are easier to iterate on locally because this takes advantage of docker image caching to avoid re-running steps when nothing has changed (whereas pre-build hooks run every time the dockerfile is built).
+
 **Warning:** It is generally recommended to avoid the need to use hooks whenever possible.
 
 ### Image-Builder

src/ubuntu/20.04/cross/arm64/Dockerfile

@@ -0,0 +1,56 @@
+FROM mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-20.04-crossdeps-local AS binutils
+
+# Install binutils-aarch64-linux-gnu
+RUN apt-get update \
+ && apt-get install -y \
+ binutils-aarch64-linux-gnu \
+ && rm -rf /var/lib/apt/lists/*
+
+
+FROM binutils AS rootfsbuild
+ARG ROOTFS_DIR=/crossrootfs
+
+# Build rootfs
+RUN git config --global user.email builder@dotnet-buildtools-prereqs-docker && \
+ git clone --depth 1 --single-branch https://github.com/dotnet/arcade /scripts
+RUN /scripts/eng/common/cross/build-rootfs.sh arm64 xenial lldb3.9 --skipunmount
+RUN bash -c "rm -rf $ROOTFS_DIR/*/{var/cache/apt/archives/*,var/lib/apt/lists/*,usr/share/doc,usr/share/man}"
+
+# Build llvm-9 compiler-rt profile library for arm64, for PGO support
+RUN wget https://github.com/llvm/llvm-project/releases/download/llvmorg-9.0.1/compiler-rt-9.0.1.src.tar.xz
+RUN tar -xf compiler-rt-9.0.1.src.tar.xz && \
+ rm compiler-rt-9.0.1.src.tar.xz
+RUN mkdir compiler-rt-build && \
+ cd compiler-rt-build && \
+ \
+ TARGET_TRIPLE=aarch64-linux-gnu \
+ BUILD_FLAGS="-v --sysroot=$ROOTFS_DIR" && \
+ \
+ cmake ../compiler-rt-9.0.1.src \
+ -DCOMPILER_RT_BUILD_PROFILE=ON \
+ -DCOMPILER_RT_BUILD_BUILTINS=OFF \
+ -DCOMPILER_RT_BUILD_SANITIZERS=OFF \
+ -DCOMPILER_RT_BUILD_XRAY=OFF \
+ -DCOMPILER_RT_BUILD_LIBFUZZER=OFF \
+ \
+ -DCMAKE_C_COMPILER=/usr/bin/clang-9 \
+ -DCMAKE_CXX_COMPILER=/usr/bin/clang++-9 \
+ -DCMAKE_EXE_LINKER_FLAGS="-fuse-ld=lld" \
+ -DCMAKE_C_COMPILER_TARGET="${TARGET_TRIPLE}" \
+ -DCMAKE_CXX_COMPILER_TARGET="${TARGET_TRIPLE}" \
+ -DCOMPILER_RT_DEFAULT_TARGET_ONLY=ON \
+ -DLLVM_CONFIG_PATH=/usr/bin/llvm-config-9 \
+ \
+ -DCMAKE_C_FLAGS="${BUILD_FLAGS}" \
+ -DCMAKE_CXX_FLAGS="${BUILD_FLAGS}"
+
+RUN cd compiler-rt-build && make
+
+# Copy profile library to the rootfs
+RUN mkdir -p $ROOTFS_DIR/usr/lib/llvm-9/lib/clang/9.0.1/lib/linux/ && \
+ cp /compiler-rt-build/lib/linux/libclang_rt.profile-aarch64.a $ROOTFS_DIR/usr/lib/llvm-9/lib/clang/9.0.1/lib/linux/
+
+
+FROM binutils
+ARG ROOTFS_DIR=/crossrootfs
+COPY --from=rootfsbuild $ROOTFS_DIR $ROOTFS_DIR

src/ubuntu/manifest.json

@@ -482,6 +482,19 @@
  }
  ]
  },
+ {
+ "platforms": [
+ {
+ "dockerfile": "src/ubuntu/20.04/cross/arm64",
+ "os": "linux",
+ "osVersion": "focal",
+ "tags": {
+ "ubuntu-20.04-cross-arm64-$(System:TimeStamp)-$(System:DockerfileGitCommitSha)": {},
+ "ubuntu-20.04-cross-arm64$(FloatingTagSuffix)": {}
+ }
+ }
+ ]
+ },
  {
  "platforms": [
  {