[llvm-dev] writing a pass, questions

[Vedant Kumar via llvm-dev]

Can you double-check the shared objects LLVMZap.so references (ldd on Linux)? If you don't see LLVM's Core and Support libraries listed, you might hit this error.

One possible fix is to add this to CMakeLists.txt:

  set(LLVM_LINK_COMPONENTS Core Support)

vedant


> On Apr 10, 2017, at 8:57 PM, Preston Briggs via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> I'm moving a couple of dynamically loaded passes 
> from an older version of LLVM to a newer one.
> I fixed various small compilation errors, and things compile now,
> but the resulting .so won't load without error.
> 
> So I re-read the manual (Writing an LLVM Pass) and tried the
> first example, Hello.cpp which produces LLVMHello.cpp
> The code's already there in the source tree and it builds
> and loads correctly. So I tried copying the directory
> and doing a little editing. It builds but again fails to load.
> 
> Here's what I type
> 
> opt -load LLVMZap.so -help
> 
> and here's what I see
> 
> Error opening 'LLVMZap.so': /home/briggs/llvm-cilk/new_install/bin/../lib/LLVMZap.so: undefined symbol: _ZNK4llvm12FunctionPass17createPrinterPassERNS_11raw_ostreamERKNSt3__112basic_stringIcNS3_11char_traitsIcEENS3_9allocatorIcEEEE
>   -load request ignored.
> 
> The error message is quite similar to what I see when I'm experimenting with my old pass.
> 
> Any ideas?
> 
> Here's the contents of CMake.txt
> 
> # If we don't need RTTI or EH, there's no reason to export anything
> # from the hello plugin.
> if( NOT LLVM_REQUIRES_RTTI )
>   if( NOT LLVM_REQUIRES_EH )
>     set(LLVM_EXPORTED_SYMBOL_FILE ${CMAKE_CURRENT_SOURCE_DIR}/Zap.exports)
>   endif()
> endif()
> 
> add_llvm_loadable_module( LLVMZap
>   Zap.cpp
> 
>   DEPENDS
>   intrinsics_gen
>   PLUGIN_TOOL
>   opt
>   )
> 
> And the contents of Zap.cpp
> 
> #include "llvm/IR/Function.h"
> #include "llvm/Pass.h"
> #include "llvm/Support/raw_ostream.h"
> using namespace llvm;
> 
> namespace {
>   struct Zap : public FunctionPass {
>     static char ID; // Pass identification, replacement for typeid
>     Zap() : FunctionPass(ID) {}
> 
>     bool runOnFunction(Function &F) override {
>       errs() << "Zap! ";
>       errs().write_escaped(F.getName()) << '\n';
>       return false;
>     }
>   };
> }
> 
> char Zap::ID = 0;
> static RegisterPass<Zap> X("zap", "Zap Pass");
> 
> Thanks,
> Preston
> 
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