toolchain.cmake: properly set toolchain for crossbuilding on Alpine Linux

[ayakael]

Port changes from dotnet/runtime#76500

Changes allow for proper toolchain detection on Alpine Linux.

/cc: @am11

[am11]

Sync changes from dotnet/runtime#76500

It was reverted dotnet/runtime#76500 (comment)?

[ayakael]

Sync changes from dotnet/runtime#76500

It was reverted dotnet/runtime#76500 (comment)?

Right, it was. Wrong word used.

[ayakael]

@am11 You had also mentionned that built-rootfs.sh should need to be tested for Alpine. Are there any other tests I need to do to confirm that these are fine? Given all of these being if-statements depending on existence of Alpine toolchain on crossrootfs, it's pretty low risk. The other part is having the x86 crosscompile settings move away from -m32 mode as Alpine doesn't support that very well.

[am11]

Yes, to keep things in sync, you can add support in build-rootfs.sh at the same time when adding support for new platform in toolchain.cmake.

For testing, I use this sort of script:

cd runtime
# make changes in build-rootfs.sh, toolchain.cmake and tryrun.cmake

# cleanup
rm -rf artifacts .tools

# replace <arch> with the arch to test
eng/common/cross/build-rootfs.sh <arch> alpine
ROOTFS_DIR=$(pwd)/.tools/rootfs/<arch> ./build.sh -cross -a <arch> -c Debug
ROOTFS_DIR=$(pwd)/.tools/rootfs/<arch> ./build.sh -cross -a <arch> -c Release

for each architecture.

Optional: if you want to add support in runtime's extra-platforms CI pipeline (which is for community supported platforms), you can send a PR to https:/dotnet/dotnet-buildtools-prereqs-docker/ (similar to dotnet/dotnet-buildtools-prereqs-docker@5291f63).

[akoeplinger]

Please ping me once this is ready and I can merge it

[ayakael]

@am11 Did you test these changes on Ubuntu? For all intents and purposes, this works for Alpine. I unfortunately don't have a Ubuntu crossbuilding environment.

[am11]

You can use a prebuilt image from https:/dotnet/versions/blob/main/build-info/docker/image-info.dotnet-dotnet-buildtools-prereqs-docker-production.json that has all the prereqs installed:

$ git clone https:/dotnet/runtime --single-branch --depth 1
$ cd runtime
# apply these changes in runtime repo
$ curl -sSL https://raw.githubusercontent.com/dotnet/arcade/b17639c6b999611cf92c01f0153b3fb3d9340e6e/eng/common/cross/toolchain.cmake -o eng/common/cross/toolchain.cmake

$ docker run -v$(pwd):/runtime --rm -it \
    mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-22.04-cross-arm64-alpine \
    /bin/bash

# inside the container; use steps from https:/dotnet/arcade/pull/11608#issuecomment-1312763905

[am11]

I ran the builds locally and changes seems to be working. Lets run a detailed test once dotnet/dotnet-buildtools-prereqs-docker#823 is in and we get the container images out of common infra (linux-musl-riscv64 image was built earlier).

@ayakael, could you please open a downstream PR in dotnet/runtime with these changes, if CI is happy we can merge these changes with confidence.

[janvorli]

I wonder why x86 alpine needs this --target option while other architectures don't

[am11]

Good question, and only used for x86 architecture. 🤔

[ayakael]

Without this, crossbuilding to x86 omits setting a target option. I presume it's because x86 is usually crosscompiled using -m32, thus doesn't require an alternate toolchain. With Alpine, I hadn't had success crossbuilding in that mode due to, I assume, not all libraries having a 32-bit version. I havn't found the particular if-statement that's to blame for omitting it

[am11]

Yup, you are right. @janvorli, without this target, build fails with linux-musl-x86 prereq image as well:

$ cd runtime
# apply patch: https:/dotnet/arcade/pull/11608 (and remove `--target` lines)

$ docker run -v$(pwd):/runtime -e ROOTFS_DIR=/crossrootfs/x86 --rm \
    mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-22.04-cross-x86-alpine \
    /runtime/build.sh clr+host+libs -a x86 -cross

[...]
  Commencing build of "install" target in "CoreCLR component" for linux.x86.Debug in /runtime/artifacts/obj/coreclr/linux.x86.Debug
  Invoking "/runtime/eng/native/gen-buildsys.sh" "/runtime/src/coreclr" "/runtime/artifacts/obj/coreclr/linux.x86.Debug" x86 linux clang Debug ""  -DCLR_CMAKE_PGO_INSTRUMENT=0 -DCLR_CMAKE_OPTDATA_PATH= -DCLR_CMAKE_PGO_OPTIMIZE=0 -DCLI_CMAKE_FALLBACK_OS="linux-musl" -DFEATURE_DISTRO_AGNOSTIC_SSL=1 
  /runtime/artifacts/obj/coreclr/linux.x86.Debug /runtime/src/coreclr
  Not searching for unused variables given on the command line.
  loading initial cache file /runtime/eng/native/tryrun.cmake
  -- The C compiler identification is Clang 15.0.7
  -- The CXX compiler identification is Clang 15.0.7
  -- Detecting C compiler ABI info
  -- Detecting C compiler ABI info - failed
  -- Check for working C compiler: /usr/bin/clang-15
  -- Check for working C compiler: /usr/bin/clang-15 - broken
  CMake Error at /usr/share/cmake-3.26/Modules/CMakeTestCCompiler.cmake:67 (message):
    The C compiler
  
      "/usr/bin/clang-15"
  
    is not able to compile a simple test program.
  
    It fails with the following output:
  
      Change Dir: /runtime/artifacts/obj/coreclr/linux.x86.Debug/CMakeFiles/CMakeScratch/TryCompile-qWpnFx
      
      Run Build Command(s):/usr/bin/cmake -E env VERBOSE=1 /usr/bin/gmake -f Makefile cmTC_66ccc/fast && /usr/bin/gmake  -f CMakeFiles/cmTC_66ccc.dir/build.make CMakeFiles/cmTC_66ccc.dir/build
      gmake[1]: Entering directory '/runtime/artifacts/obj/coreclr/linux.x86.Debug/CMakeFiles/CMakeScratch/TryCompile-qWpnFx'
      Building C object CMakeFiles/cmTC_66ccc.dir/testCCompiler.c.o
      /usr/bin/clang-15 --gcc-toolchain=/crossrootfs/x86/usr --sysroot=/crossrootfs/x86   -m32 -Wno-error=unused-command-line-argument -MD -MT CMakeFiles/cmTC_66ccc.dir/testCCompiler.c.o -MF CMakeFiles/cmTC_66ccc.dir/testCCompiler.c.o.d -o CMakeFiles/cmTC_66ccc.dir/testCCompiler.c.o -c /runtime/artifacts/obj/coreclr/linux.x86.Debug/CMakeFiles/CMakeScratch/TryCompile-qWpnFx/testCCompiler.c
      Linking C executable cmTC_66ccc
      /usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_66ccc.dir/link.txt --verbose=1
      /usr/bin/clang-15 --gcc-toolchain=/crossrootfs/x86/usr --sysroot=/crossrootfs/x86 -Wl,--rpath-link=/crossrootfs/x86/lib/i586-alpine-linux-musl -Wl,--rpath-link=/crossrootfs/x86/usr/lib/i586-alpine-linux-musl -Wl,--rpath-link=/crossrootfs/x86/usr/lib/gcc/i586-alpine-linux-musl -m32 -Wl,--rpath-link=/crossrootfs/x86/lib/i586-alpine-linux-musl -Wl,--rpath-link=/crossrootfs/x86/usr/lib/i586-alpine-linux-musl -Wl,--rpath-link=/crossrootfs/x86/usr/lib/gcc/i586-alpine-linux-musl -m32 -fuse-ld=lld  CMakeFiles/cmTC_66ccc.dir/testCCompiler.c.o -o cmTC_66ccc 
      ld.lld: error: cannot open crtbeginS.o: No such file or directory
      ld.lld: error: unable to find library -lgcc
      ld.lld: error: unable to find library -lgcc
      ld.lld: error: cannot open crtendS.o: No such file or directory
      clang: error: linker command failed with exit code 1 (use -v to see invocation)
      gmake[1]: *** [CMakeFiles/cmTC_66ccc.dir/build.make:100: cmTC_66ccc] Error 1
      gmake[1]: Leaving directory '/runtime/artifacts/obj/coreclr/linux.x86.Debug/CMakeFiles/CMakeScratch/TryCompile-qWpnFx'
      gmake: *** [Makefile:127: cmTC_66ccc/fast] Error 2
      
      
  
    
  
    CMake will not be able to correctly generate this project.
  Call Stack (most recent call first):
    CMakeLists.txt:16 (project)
  
  
  -- Configuring incomplete, errors occurred!
  /runtime/src/coreclr
  /runtime/artifacts/obj/coreclr/linux.x86.Debug /runtime/src/coreclr
  Executing make install -j 16
  make: *** No rule to make target 'install'.  Stop.
  /runtime/src/coreclr
  Failed to build "CoreCLR component".
/runtime/src/coreclr/runtime.proj(62,5): error MSB3073: The command ""/runtime/src/coreclr/build-runtime.sh" -x86 -debug -cross -os linux -outputrid linux-musl-x86" exited with code 2.

[am11]

@janvorli if there is no other feedback, can this be merged?

[janvorli]

@am11 sure, I am sorry for the delay. It just needs to be updated to the latest main. I'll do it using github.

[janvorli]

LGTM, thank you!