How to get the address of a global variable in LLVM? - llvm

Question

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!

Answer 1

Two possibilities either you are passing parameters of different type or of different size.
I am not quite sure but try this:
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());
std::vector<Value *> args;
args.push_back(po);
builder.CreateCall(instrument_func, args);
}
}