[cfe-dev] Linking a plugin against clang/LLVM libraries

[Ehsan Akhgari]

Hi all,

I'm trying to compile a clang plugin against a local ToT build of clang on
OSX 10.10.  The link command fails like this:

$ /Users/ehsan/src/llvm-objdir/bin/clang++ -Qunused-arguments
-I/Users/ehsan/src/llvm/include -I/Users/ehsan/src/llvm-objdir/include
-fPIC -fvisibility-inlines-hidden -Wall -W -Wno-unused-parameter
-Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic
-Wno-long-long -Wcovered-switch-default -std=c++11 -fcolor-diagnostics -O2
-g -DNDEBUG  -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS
-D__STDC_LIMIT_MACROS -fno-rtti -fno-exceptions -fno-omit-frame-pointer
-fPIC -shared -o libclang-plugin.dylib  clang-plugin.o
-L/Users/ehsan/src/llvm-objdir/lib -Wl,-search_paths_first
-Wl,-headerpad_max_install_names -lcurses -lpthread -lz -lm
-L/Users/ehsan/src/llvm-objdir/lib -Wl,-search_paths_first
-Wl,-headerpad_max_install_names -lLLVMOption -lLLVMBitReader
-lLLVMMCParser -lLLVMAsmParser -lLLVMAnalysis -lLLVMTarget -lLLVMMC
-lLLVMCore -lLLVMSupport -lclangFrontend -lclangDriver -lclangSerialization
-lclangParse -lclangSema -lclangAnalysis -lclangEdit -lclangAST -lclangLex
-lclangBasic -lclangASTMatchers
-Wl,-executable_path,/Users/ehsan/moz/src/obj-ff-clang-plugin.noindex/dist/bin
-dynamiclib -install_name @executable_path/libclang-plugin.dylib
-compatibility_version 1 -current_version 1 -single_module
Undefined symbols for architecture x86_64:
  "llvm::MemoryBuffer::getOpenFile(int, llvm::Twine const&, unsigned long
long, bool, bool)", referenced from:
      (anonymous namespace)::RealFile::getBuffer(llvm::Twine const&, long
long, bool, bool) in libclangBasic.a(VirtualFileSystem.cpp.o)
  "llvm::MemoryBuffer::getMemBufferCopy(llvm::StringRef, llvm::Twine
const&)", referenced from:
      clang::Preprocessor::EnterMainSourceFile() in
libclangLex.a(Preprocessor.cpp.o)
      clang::createChainedIncludesSource(clang::CompilerInstance&,
llvm::IntrusiveRefCntPtr<clang::ExternalSemaSource>&) in
libclangFrontend.a(ChainedIncludesSource.cpp.o)

clang::ASTUnit::getMainBufferWithPrecompiledPreamble(clang::CompilerInvocation
const&, bool, unsigned int) in libclangFrontend.a(ASTUnit.cpp.o)

clang::GenerateModuleAction::BeginSourceFileAction(clang::CompilerInstance&,
llvm::StringRef) in libclangFrontend.a(FrontendActions.cpp.o)
  "llvm::MemoryBuffer::getNewUninitMemBuffer(unsigned long, llvm::Twine
const&)", referenced from:
      clang::Preprocessor::SetCodeCompletionPoint(clang::FileEntry const*,
unsigned int, unsigned int) in libclangLex.a(Preprocessor.cpp.o)
  "llvm::MemoryBuffer::getFile(llvm::Twine const&, long long, bool, bool)",
referenced from:
      clang::CompilerInvocation::getModuleHash() const in
libclangFrontend.a(CompilerInvocation.cpp.o)
      clang::createVFSFromCompilerInvocation(clang::CompilerInvocation
const&, clang::DiagnosticsEngine&) in
libclangFrontend.a(CompilerInvocation.cpp.o)
      clang::GlobalModuleIndex::readIndex(llvm::StringRef) in
libclangSerialization.a(GlobalModuleIndex.cpp.o)
      clang::PTHManager::Create(std::__1::basic_string<char,
std::__1::char_traits<char>, std::__1::allocator<char> > const&,
clang::DiagnosticsEngine&) in libclangLex.a(PTHLexer.cpp.o)
      clang::driver::toolchains::Linux::Linux(clang::driver::Driver const&,
llvm::Triple const&, llvm::opt::ArgList const&) in
libclangDriver.a(ToolChains.cpp.o)
  "llvm::sys::findProgramByName(llvm::StringRef,
llvm::ArrayRef<llvm::StringRef>)", referenced from:
      clang::driver::Driver::GetProgramPath(char const*,
clang::driver::ToolChain const&) const in libclangDriver.a(Driver.cpp.o)
  "llvm::scalbn(llvm::APFloat, int)", referenced from:
      (anonymous
namespace)::ComplexExprEvaluator::VisitBinaryOperator(clang::BinaryOperator
const*) in libclangAST.a(ExprConstant.cpp.o)
  "llvm::APInt::sshl_ov(llvm::APInt const&, bool&) const", referenced from:
      EvaluateDirectiveSubExpr((anonymous namespace)::PPValue&, unsigned
int, clang::Token&, bool, clang::Preprocessor&) in
libclangLex.a(PPExpressions.cpp.o)
  "llvm::APInt::ushl_ov(llvm::APInt const&, bool&) const", referenced from:
      EvaluateDirectiveSubExpr((anonymous namespace)::PPValue&, unsigned
int, clang::Token&, bool, clang::Preprocessor&) in
libclangLex.a(PPExpressions.cpp.o)
ld: symbol(s) not found for architecture x86_64
clang-3.5: error: linker command failed with exit code 1 (use -v to see
invocation)

The missing symbols are all in libLLVMSupport.a, but libLLVMSupport.dylib
(which is the library that ld tries to link against) misses all of these
symbols because they are not referenced by anything and were eliminated
during linking.

tools/driver/CMakeLists.txt in the clang repository sets LLVM_NO_DEAD_STRIP
to 1 if CLANG_PLUGIN_SUPPORT is turned on, which it is in my build, but it
seems like that setting does not affect libLLVMSupport, so we end up
passing -dead_strip to the linker.  I'm not sure if this is the intended
behavior, or a bug.

Do I understand the setup as intended correctly?  Can someone please
suggest a way to bypass this issue?

Thanks!
-- 
Ehsan
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