[llvm-dev] Moving to ORCv2 - Where are my global constructors and destructors?

Gaier, Bjoern via llvm-dev llvm-dev at lists.llvm.org
Thu Dec 19 05:53:38 PST 2019


Recently I tried out the ORCv2 JIT, especially the LLJIT. I gotta say, that I really like the new interface and the way you use it! However there is one thing I'm missing. I wrote a small bit code file, which should force having a global constructor.

int wuff();

__declspec(noinline) int miau()
       return wuff();

const int x = miau();

When I parse this IR file in my JIT and go through the 'globals()' of the llvm::Module, then I will encounter a symbol with the following name:
"_GLOBAL__sub_I_VectorBIOS.cpp" where VectorBIOS.cpp was the name of the source file I compiled to the bit code.

I then wanted to get the address of that symbol - from the MCJIT times I remember, that those functions are the global constructors, but when calling lookup on that name, I was not able to find the symbol.
So I tried a different way:
llvm::GlobalVariable *var = module->getNamedGlobal("llvm.global_ctors");
       llvm::ConstantArray *InitList = (llvm::ConstantArray*)var->getInitializer();
       for(unsigned int n = 0; n < InitList->getNumOperands(); n++)
             llvm::ConstantStruct *CS = (llvm::ConstantStruct*)InitList->getOperand(n);

             llvm::Constant *FP = CS->getOperand(1);

             llvm::ConstantExpr *CE = (llvm::ConstantExpr*)FP;
                    FP = CE->getOperand(0);

I then printed the name of the llvm::Function but it was exactly the name I expected "_GLOBAL__sub_I_VectorBIOS.cpp". This code was executed before I added module to the JIT.
For various reasons I wanted to store the address to the constructor - so I don't want to call the LLJIT runConstructor - simply because I want to execute those functions later, when the LLJIT does not exist anymore.

I hope someone can help me with this...

Kind Greetings
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