LLVM gets argument values ​​of declared function at runtime

Question

I am writing an LLVM pass that should receive the values ​​passed to the declared function and say print them. Note that the declared function is called in the LLVM IR.

I wrote a module pass to repeat all the instructions in the program. The fragment for receiving the arguments of the called function in the instruction is as follows:

for (auto &B: F){
                for (auto &I: B){
                    if (auto *InvokeI = dyn_cast <InvokeInst>(&I)) { 
                       if (InvokeI->getCalledFunction()->getName().str() == "function_name") {
                            errs() << "===\n";
                            errs() << *(InvokeI->getOperand(0)) <<"\n";
                            errs() << *(InvokeI->getOperand(1)) <<"\n";
                            errs() << *(InvokeI->getOperand(2)) <<"\n";
                       }
                    }
                }

}

However, if the LLVM IR for the called function looks something like this:

invoke void @function_name(i8* %4, i8* bitcast (i8** @_ZTIi to i8*), i8* null) #5
          to label %36 unwind label %6

then my code snippets above are output:

%4 = call i8* @__cxa_allocate_exception(i64 4) #2
i8* bitcast (i8** @_ZTIi to i8*)
i8* null

Instead of displaying the actual value that is passed during the function call.

My question is: how do we get the values ​​that are passed at runtime. Is there a way to add a function body to declared functions that return nothing?

Any help on this is appreciated, thanks

Answer 1

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