ci: experiment with new mingw clang64 by SchrodingerZhu · Pull Request #808 · microsoft/snmalloc

SchrodingerZhu · 2026-01-29T14:53:03Z

Add a clang64 based mingw CI.

This should follow #806

SchrodingerZhu · 2026-01-29T15:09:53Z

It seems that mingw-clang64 works OOB now.

However, there is a cmake issue that I do not understand:

 C:\Windows\system32\cmd.exe /C "cd . && C:\PROGRA~1\LLVM\bin\CLANG_~1.EXE -nostartfiles -nostdlib -O0 -g -Xclang -gcodeview -D_DEBUG -D_DLL -D_MT -Xclang --dependent-lib=msvcrtd -Xlinker /subsystem:console  -Wl,--no-undefined /DEBUG -rdynamic -fuse-ld=lld-link CMakeFiles/perf-contention-fast.dir/src/test/perf/contention/contention.cc.obj -o perf-contention-fast.exe -Xlinker /MANIFEST:EMBED -Xlinker /implib:perf-contention-fast.lib -Xlinker /pdb:perf-contention-fast.pdb -Xlinker /version:0.0   -lmincore.lib  -lkernel32 -luser32 -lgdi32 -lwinspool -lshell32 -lole32 -loleaut32 -luuid -lcomdlg32 -ladvapi32 -loldnames  && cd ."
clang++: error: no such file or directory: '/DEBUG'

By using if (NOT MINGW) , this should already be eliminated. For some reasons, the change does not apply here.

cc @mjp41

ryancinsight · 2026-01-29T16:16:57Z

It seems that mingw-clang64 works OOB now.

However, there is a cmake issue that I do not understand:

 C:\Windows\system32\cmd.exe /C "cd . && C:\PROGRA~1\LLVM\bin\CLANG_~1.EXE -nostartfiles -nostdlib -O0 -g -Xclang -gcodeview -D_DEBUG -D_DLL -D_MT -Xclang --dependent-lib=msvcrtd -Xlinker /subsystem:console  -Wl,--no-undefined /DEBUG -rdynamic -fuse-ld=lld-link CMakeFiles/perf-contention-fast.dir/src/test/perf/contention/contention.cc.obj -o perf-contention-fast.exe -Xlinker /MANIFEST:EMBED -Xlinker /implib:perf-contention-fast.lib -Xlinker /pdb:perf-contention-fast.pdb -Xlinker /version:0.0   -lmincore.lib  -lkernel32 -luser32 -lgdi32 -lwinspool -lshell32 -lole32 -loleaut32 -luuid -lcomdlg32 -ladvapi32 -loldnames  && cd ."
clang++: error: no such file or directory: '/DEBUG'

By using if (NOT MINGW) , this should already be eliminated. For some reasons, the change does not apply here.

cc @mjp41

could be this in cmakelists: target_link_options(${name} PRIVATE
$<$BOOL:${SNMALLOC_LINKER_SUPPORT_NO_ALLOW_SHLIB_UNDEF}:-Wl,--no-undefined>
$<$<PLATFORM_ID:Windows>:$<${ci_or_debug}:/DEBUG>>)
while I think you want: $<$<PLATFORM_ID:Windows>:$<${ci_or_debug}:LINKER:/DEBUG>>

SchrodingerZhu · 2026-01-30T15:45:08Z

I think it is working now.

lhmouse · 2026-02-03T02:53:00Z

If you mean to use C:\Program Files\LLVM\bin\clang++.exe then it's not MinGW clang; it's Clang-CL, because it links against MSVC CRT by default.

If you want to use clang that has a MinGW target by default, you should use MSYS2 CLANG64 shell.

SchrodingerZhu · 2026-02-03T03:45:51Z

@lhmouse ah, nice catch. I just found that I deleted the shell command mistakenly.

SchrodingerZhu · 2026-02-03T04:13:06Z

I currently have a full time table. I may need more time to work on this.

SchrodingerZhu · 2026-02-03T04:42:44Z

@lhmouse also feel free to patch on top of this if you are interested and available.

Really a nice catch ... It turns out I was running clang-cl outside MSYS...... No wonder the if (MINGW) check was not working :).

lhmouse · 2026-02-03T04:45:04Z

If you really mean to call the msys2 clang, you should set CMAKE_<LANG>_COMPILER to absolute paths.

SchrodingerZhu · 2026-02-03T05:07:11Z

If you really mean to call the msys2 clang, you should set CMAKE_<LANG>_COMPILER to absolute paths.

shell: msys2 {0} is good enough according to my previous experience. The new problem is actually that we DO HAVE compatibility issue in current setup.

Copilot

Pull request overview

This PR adds experimental MinGW Clang64 CI support following the refactored CI structure from PR #806. The changes enable building and testing snmalloc on Windows using MSYS2's Clang64 environment, which is a different toolchain from the existing MSVC-based Windows builds.

Changes:

Added a new MinGW Clang64 GitHub Actions workflow with Debug and RelWithDebInfo build profiles
Updated CMake to add -fms-extensions flag for Clang on MinGW to enable Microsoft pragma support
Changed linker flag syntax from /DEBUG to LINKER:/DEBUG for better cross-linker compatibility
Excluded MS-specific pragmas (pragma warning and pragma init_seg) from MinGW builds
Disabled the protect_fork test on MinGW since fork functionality doesn't work on this platform

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 8 comments.

File	Description
.github/workflows/mingw.yml	New workflow for MinGW Clang64 CI with matrix builds for Debug and RelWithDebInfo profiles
CMakeLists.txt	Added `-fms-extensions` for MinGW Clang and fixed linker flag syntax for cross-platform compatibility
src/snmalloc/pal/pal_windows.h	Excluded MSVC-specific pragmas from MinGW builds to avoid compiler errors
src/test/func/protect_fork/protect_fork.cc	Skip test on MinGW where fork() is not supported

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Copilot · 2026-02-03T17:05:09Z

.github/workflows/mingw.yml

+          cmake 
+          --build "$(cygpath -u "$GITHUB_WORKSPACE")/build"
+          --parallel
+


There is trailing whitespace at the end of this line. Removing it would improve consistency.

Suggested change

Copilot · 2026-02-03T17:05:10Z

.github/workflows/mingw.yml

+        run: |
+          cd "$(cygpath -u "$GITHUB_WORKSPACE")/build"
+          ctest
+


There is trailing whitespace at the end of this line. Removing it would improve consistency.

Suggested change

Copilot · 2026-02-03T17:05:10Z

.github/workflows/mingw.yml

+          -B"$(cygpath -u "$GITHUB_WORKSPACE")/build"
+          -DCMAKE_BUILD_TYPE=${{ matrix.profile }}
+          -DCMAKE_CXX_COMPILER=clang++
+          -DCMAKE_C_COMPILER=clang


The configure step is missing the -DSNMALLOC_CI_BUILD=ON flag that is consistently used in other CI workflows. This flag enables additional debug information and backtrace support in CI builds, which would be beneficial for debugging failures in this workflow as well.

Suggested change

-DCMAKE_C_COMPILER=clang

-DCMAKE_C_COMPILER=clang

-DSNMALLOC_CI_BUILD=ON

Copilot · 2026-02-03T17:05:10Z

.github/workflows/mingw.yml

+        shell: msys2 {0}
+        run: |
+          cd "$(cygpath -u "$GITHUB_WORKSPACE")/build"
+          ctest


The ctest invocation is missing common flags used in other workflows. It should include --output-on-failure to provide better debugging information when tests fail, -j 4 for parallel execution, and --timeout 400 to prevent hanging tests. For consistency with other workflows (see .github/workflows/reusable-cmake-build.yml:115), consider using: ctest --output-on-failure -j 4 -C ${{ matrix.profile }} --timeout 400

Suggested change

ctest

ctest --output-on-failure -j 4 -C ${{ matrix.profile }} --timeout 400

Copilot · 2026-02-03T17:05:11Z

.github/workflows/mingw.yml

+        profile: [RelWithDebInfo, Debug]
+
+    name: MinGW Clang64 Build (${{ matrix.profile }})
+    runs-on: windows-2025


The job is missing a timeout-minutes configuration. Other workflows in this repository consistently set timeout-minutes (e.g., 30 minutes for similar build jobs in reusable-cmake-build.yml). This is important to prevent jobs from hanging indefinitely and consuming runner resources.

Suggested change

runs-on: windows-2025

runs-on: windows-2025

timeout-minutes: 30

Copilot · 2026-02-03T17:05:11Z

CMakeLists.txt

+
  target_link_options(${name} PRIVATE 


There is trailing whitespace at the end of this line. While this doesn't affect functionality, removing it would improve code consistency.

Suggested change

target_link_options(${name} PRIVATE

target_link_options(${name} PRIVATE

Copilot · 2026-02-03T17:05:12Z

.github/workflows/mingw.yml

+
+      - name: Setup MSYS2
+        id: msys2
+        uses: msys2/setup-msys2@v2


There is an extra blank line here. For consistency with other workflow files in the repository, there should be a single blank line between steps.

Suggested change

- name: Setup MSYS2

id: msys2

uses: msys2/setup-msys2@v2

- name: Setup MSYS2

id: msys2

uses: msys2/setup-msys2@v2

uses: msys2/setup-msys2@v2

Copilot · 2026-02-03T17:05:12Z

.github/workflows/mingw.yml

+
+    name: MinGW Clang64 Build (${{ matrix.profile }})
+    runs-on: windows-2025
+


There is trailing whitespace at the end of this line. Removing it would improve consistency.

SchrodingerZhu marked this pull request as ready for review January 29, 2026 15:11

This was referenced Jan 29, 2026

investigate the problem on MinGW #217

Closed

Mingw support (2022-1) #451

Closed

SchrodingerZhu mentioned this pull request Jan 30, 2026

Refactor CI #806

Merged

SchrodingerZhu added 5 commits February 2, 2026 22:49

ci: experiment with new mingw clang64

aa5245f

fix

22fe051

try fix

5151829

Update mingw.yml to use msys2 shell for commands

f270b4e

allow MS extensions with MinGW

fa486a2

SchrodingerZhu force-pushed the ci/mingw-clang64 branch from 7a8b2e1 to fa486a2 Compare February 3, 2026 03:55

skip .CRT$XCB

77af0b5

SchrodingerZhu marked this pull request as draft February 3, 2026 04:12

SchrodingerZhu added 6 commits February 3, 2026 09:45

Update preprocessor directive for pthread atfork check

14ccc57

Simplify directory change command in workflow

4276e58

Fix path for build directory in Mingw workflow

2c663c1

debug

38a5a41

Fix conditional compilation for pthread_atfork

a1fa459

fix

089385a

SchrodingerZhu marked this pull request as ready for review February 3, 2026 15:54

SchrodingerZhu requested review from Copilot and mjp41 February 3, 2026 16:59

Copilot started reviewing on behalf of SchrodingerZhu February 3, 2026 17:00 View session

Copilot AI reviewed Feb 3, 2026

View reviewed changes

	-DCMAKE_C_COMPILER=clang
	-DCMAKE_C_COMPILER=clang
	-DSNMALLOC_CI_BUILD=ON

	ctest
	ctest --output-on-failure -j 4 -C ${{ matrix.profile }} --timeout 400

	runs-on: windows-2025
	runs-on: windows-2025
	timeout-minutes: 30


	target_link_options(${name} PRIVATE

	target_link_options(${name} PRIVATE


		name: MinGW Clang64 Build (${{ matrix.profile }})
		runs-on: windows-2025

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