Clang won't run example plugins on windows.

I have cloned the llvm-project repository.

Then I have generated a Visual Studio solution for the project using:


The important part is DLLVM_EXPORT_SYMBOLS_FOR_PLUGINS, as suggested here:

The solution and all the projects are generated. Then I build Clang itself and an example clang plugin that is already provided in the llvm-project source. The PrintFunctionNames seem to be the hello world of Clang plugins, so I have built that, according to the llvm documentation.

The build successfully ran, and now I have llvm/clang in the install dir, with the PrintFunctionNames plugin.

The problem is that I can not invoke the plugin. As far as I know, there is 3 ways to tell calng to use your plugin.

  • The cc1 interface:

I can call my plugin with:

clang -cc1 -load PrintFunctionNames.dll -plugin print-fns test.cpp

This only works with clang and won’t work with clang++. Moreover, clang won’t find the standard headers, but that is expected behaviour with cc1 according to the documentation.

  • The -Xclang interface:
I call my plugin with:
clang -Xclang -load -Xclang PrintFunctionNames.dll -Xclang -plugin -Xclang print-fns test.cpp
This works aswell, and since Xclang appends to the cc1, standard library headers are found too. However, calling clang++ instead of clang won’t work here either. Clang++ outputs an error: unable to find plugin 'print-fns'.

-          The fplugin interface:
I have added the necessary code according to the documentation:

// Automatically run the plugin after the main AST action

PluginASTAction::ActionType getActionType() override {

return AddAfterMainAction;


After that, I can run the plugin with:

clang -fplugin=PrintFunctionNames.dll test.cpp

This runs as expected, but once again, clang++ wont run the plugin. Moreover, no error messages are generated, clang++ just refuses to run the plugin.

I do not understand why clang seems to work fine with plugins, but clang++ refuses to run any. I have tried all the provided example plugins, none of them works with clang++, while all of them works as expected with clang.

I have tested both the latest version and llvm 11 too, I am using windows 10.

I would really appreciate any insights as to why clang++ would behave differently when it comes to plugins.

One difficulty with plugins on Windows is that the plugin dll needs to
know which executable it is loaded into. This is specified by the
PLUGIN_TOOL argument to add_llvm_library. For the hello world example,
it is:

add_llvm_library(PrintFunctionNames [...] PLUGIN_TOOL clang)

That is, it will only work when loaded by the "clang.exe" executable.
Just renaming clang.exe to something else would already break it, as
you observed with "clang++.exe".

A proper solution would be to build a libLLVM.dll and use that as
"PLUGIN_TOOL", all executables would import that dll instead of
statically linking it. However, we encounter the next problem: Windows
dlls only allow up 2^16 exported symbols and libLLVM.dll would require
more, which is why LLVM_BUILD_LLVM_DYLIB=ON is not supported under