Undefined symbol when loading LLVM plugin - c++

Question

I am developing an LLVM pass and want to run it as a plugin via the Clang LLVM driver:
clang -Xclang -load -Xclang myPlugin.so ...
At first I got an error similar to that described here
undefined symbol for self-built llvm opt?
After applying the flag -D_GLIBCXX_USE_CXX11_ABI=0 as suggested, I'm getting this error:
error: unable to load plugin 'myPlugin.so': 'myPlugin.so: undefined symbol: _ZNK4llvm12FunctionPass17createPrinterPassERNS_11raw_ostreamERKSs
This page suggests that there may be an ABI compatibility issue (which I don't fully understand)
http://clang-developers.42468.n3.nabble.com/Loading-Static-Analyzer-plugin-fails-with-CommandLine-Errors-td4034194.html
My objective is to compile the pass with either GCC or Clang and run it with the system Clang installation (Ubuntu 16.04, LLVM 3.8) rather than building Clang/LLVM from source.

Answer 1

The problem could come from multiple clang installations. The clang version you have used to compile your plugin may be different from the clang called in
clang -Xclang -load -Xclang myPlugin.so ...
If you use cmake to build your plugin, then
cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=ON
will generate the file compile_commands.json that will contain the llvm version you have used. bear make or make -n are alternatives if you don't use cmake for your plugin.
If compile_commands.json contains for example
"command": "c++ -c -I/usr/lib/llvm-4.0/include ..."
and if clang -v is clang version 3.8.0, you are likely to obtain this error message especially if llvm::FunctionPass::createPrinterPass is in llvm-4.0 and not in llvm-3.8.
A solution may be to compile with
clang-xxx -Xclang -load -Xclang myPlugin.so ...
where clang-xxx contains the llvm-xxx that is referenced in compile_commands.json.

Answer 2

I was receiving that error because first argument I passed into the RegisterPass had the same name as the pass itself:
static RegisterPass<MyPass> X("MyPass", "DPVariableNamePass", false, false);
Changing it fixed the issue:
static RegisterPass<MyPass> X("my-pass", "DPVariableNamePass", false, false);
Maybe it helps