ubuntu-22.04-cross-arm-alpine container missing armv7-alpine-linux-musleabihf-* toolchain symlinks

[udlose]

ubuntu-22.04-cross-arm-alpine container missing armv7-alpine-linux-musleabihf-* toolchain symlinks

Summary

The ubuntu-22.04-cross-arm-alpine container has a toolchain naming mismatch that prevents .NET 6 runtime builds from succeeding. CMake expects armv7-alpine-linux-musleabihf-* tools but the container only provides armv7-alpine-linux-musl-* tools, causing build failures.

Environment

• Container Image: mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-22.04-cross-arm-alpine
• Build Target: .NET 6 Runtime (dotnet/runtime v6.0.36)
• Architecture: ARM32 (cross-compilation from x64)
• Build System: CMake + MSBuild
• Build Configuration: Release
• Target OS: Linux
• Runtime Flavor: CoreCLR
• ROOTFS_DIR: /crossrootfs/arm

Expected Behavior

The container should provide cross-compilation tools with the naming convention that CMake expects:

• armv7-alpine-linux-musleabihf-objcopy
• armv7-alpine-linux-musleabihf-gcc
• armv7-alpine-linux-musleabihf-g++
• etc.

Actual Behavior

The build fails during the CoreCLR native compilation phase with this exact error:

Invoking "/__w/dotnet-nes-build/dotnet-nes-build/rt/eng/native/gen-buildsys.sh" "/__w/dotnet-nes-build/dotnet-nes-build/rt/src/coreclr" "/__w/dotnet-nes-build/dotnet-nes-build/rt/artifacts/obj/coreclr/Linux.arm.Release" arm clang "" "" Release ""  -DCLR_CMAKE_PGO_INSTRUMENT=0 -DCLR_CMAKE_OPTDATA_PATH= -DCLR_CMAKE_PGO_OPTIMIZE=1 -DFEATURE_DISTRO_AGNOSTIC_SSL=1

CMake Error at /__w/dotnet-nes-build/dotnet-nes-build/rt/eng/native/configuretools.cmake:37 (message):
  Unable to find toolchain executable.  Name: objcopy, Prefix:
  armv7-alpine-linux-musleabihf-.
Call Stack (most recent call first):
  /__w/dotnet-nes-build/dotnet-nes-build/rt/eng/native/configuretools.cmake:63 (locate_toolchain_exec)
  /__w/dotnet-nes-build/dotnet-nes-build/rt/eng/native/configurecompiler.cmake:1 (include)
  CMakeLists.txt:19 (include)

-- Configuring incomplete, errors occurred!
make: *** No rule to make target 'install'.  Stop.
##vso[task.logissue type=error]Failed to build "CoreCLR component".

Build Command That Fails:

./build.sh \
  --restore \
  --build \
  --subset clr+libs+host+packs \
  --os Linux \
  --arch arm \
  --ci \
  --pack \
  --cross \
  --runtimeFlavor coreclr \
  --configuration Release \
  --librariesConfiguration Release \
  --runtimeConfiguration Release \
  /p:OfficialBuildId=XXXXXXXX.YY

Evidence of the Problem

Investigation of the container shows the tools exist but with incorrect naming:

Container Investigation Results

# ROOTFS_DIR is correctly set up
$ ls -la /crossrootfs/arm/
drwxr-xr-x 19 root root 4096 Feb  4 21:00 .
drwxr-xr-x  3 root root 4096 Feb  4 21:08 ..
drwxr-xr-x  2 root root 4096 Feb  4 21:00 bin
# ... (complete Alpine rootfs structure exists)

# Alternative toolchain exists in crossrootfs but with different path
$ find /crossrootfs/arm -name "*objcopy*" 2>/dev/null
/crossrootfs/arm/usr/bin/objcopy
/crossrootfs/arm/usr/armv7-alpine-linux-musleabihf/bin/objcopy  # ✅ Correct name but wrong PATH

Available Tools (Wrong Names)

$ find /usr -name "*objcopy*" 2>/dev/null
/usr/bin/armv7-alpine-linux-musl-objcopy     # ❌ Wrong name
/usr/bin/arm-linux-gnueabihf-objcopy
/usr/bin/objcopy
...

$ find /usr -name "*arm*" -type f -executable 2>/dev/null | head -10
/usr/bin/armv7-alpine-linux-musl-ld          # ❌ All have 'musl' not 'musleabihf'
/usr/bin/armv7-alpine-linux-musl-ar
/usr/bin/armv7-alpine-linux-musl-objcopy
/usr/bin/armv7-alpine-linux-musl-gcc
...

Expected Tools (Missing)

$ command -v armv7-alpine-linux-musleabihf-objcopy
# (not found)

Workaround Confirmation

Creating symlinks resolves the issue:

$ ln -sf /usr/bin/armv7-alpine-linux-musl-objcopy /usr/bin/armv7-alpine-linux-musleabihf-objcopy
$ command -v armv7-alpine-linux-musleabihf-objcopy
/usr/bin/armv7-alpine-linux-musleabihf-objcopy
$ armv7-alpine-linux-musleabihf-objcopy --version
GNU objcopy (GNU Binutils) 2.39

Comparison with Working ARM64 Container

The ARM64 equivalent (ubuntu-22.04-cross-arm64-alpine) works correctly and uses the musl naming convention (not musleabihf), but CMake expects different conventions for ARM32 vs ARM64:

• ARM64 Expected: aarch64-alpine-linux-musl-* ✅ (matches what's available)
• ARM32 Expected: armv7-alpine-linux-musleabihf-* ❌ (doesn't match what's available)

This suggests the ARM32 container build process is missing the creation of the expected symlinks.

Impact

• ❌ Blocks .NET 6 runtime builds for ARM32 Alpine targets
• ❌ Affects any project using this container for ARM32 cross-compilation
• ✅ ARM64 builds work fine (different naming convention)

Workaround

Add these symlinks in the build process:

ln -sf /usr/bin/armv7-alpine-linux-musl-objcopy /usr/bin/armv7-alpine-linux-musleabihf-objcopy
ln -sf /usr/bin/armv7-alpine-linux-musl-gcc /usr/bin/armv7-alpine-linux-musleabihf-gcc
ln -sf /usr/bin/armv7-alpine-linux-musl-g++ /usr/bin/armv7-alpine-linux-musleabihf-g++

Suggested Fix

The container should include symlinks for all armv7-alpine-linux-musl-* tools to their armv7-alpine-linux-musleabihf-* equivalents, similar to how other cross-compilation containers handle naming conventions.

References

• Similar toolchain fix for ARM64: [PR #112](Fix Alpine ARM64 crossbuild by updating binutils #112)
• ARM toolchain discussions: [PR #695](Add step for binutils build in cross-arm{64}-alpine #695)

Additional Context

This issue was discovered while building the .NET 6 runtime source.

Workflow Context:

• Building in GitHub Actions using the official Microsoft container
• Cross-compiling from Ubuntu 22.04 x64 host to ARM32 Alpine target
• ARM64 equivalent job succeeds using ubuntu-22.04-cross-arm64-alpine container
• Building multiple architectures: x64 ✅, ARM64 ✅, ARM32 ❌
• Same build script and parameters work for all other architectures

GitHub Actions Environment:

container:
  image: mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-22.04-cross-arm-alpine
  options: --user root
env:
  BUILD_ARCH: 'arm'
  RUNTIME_FLAVOR: 'coreclr'
  ROOTFS_DIR: '/crossrootfs/arm'

The ARM64 equivalent build works perfectly, suggesting this is a container-specific issue rather than a fundamental toolchain problem.

[mthalman]

[Triage] Given that .NET 6 is EOL, we're no longer maintaining the images here to be compatible with that version. The recommendation is to build your own image to support that. You can use the pattern used in the Dockerfiles here as a starting point.