[llvm-dev] How to get the address of a global variable in LLVM? (original) (raw)

Dipanjan Das via llvm-dev llvm-dev at lists.llvm.org
Fri Apr 28 14:20:40 PDT 2017

Let x be the address of a global variable g in a program at run-time. LLVM IR produces a store instruction as shown below:

store i32 30, i32* @g, align 4

I am writing an LLVM pass which will instrument the program such that x is passed to an instrumentation function func(int addr) at run-time. I can insert a call to func using IRBuilder successfully. What I am not being able to do is to insert instrumentation to collect x.

if (StoreInst *store_inst = dyn_cast<StoreInst>(&I)) {

                    Value* po = store_inst->getPointerOperand();
                    if(isa<GlobalVariable>(po)) {
                        errs() << "store [pointer]: " << *po << '\n';

                        Constant *instrument_func =

F.getParent()->getOrInsertFunction("func", Type::getVoidTy(Ctx), Type::getInt32Ty(Ctx), NULL);

                        IRBuilder<> builder(&I);
                        builder.SetInsertPoint(&B,

++builder.GetInsertPoint());

                        Value* args[] = {po};
                        builder.CreateCall(instrument_func, args);
                    }
                }

The result of running opt is :

Call parameter type does not match function signature!
i32* @a
 i32  call void bitcast (void (i64)* @func to void (i32)*)(i32* @a)
LLVM ERROR: Broken function found, compilation aborted!

--

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