[llvm-dev] How to instrument a module to spit out the addresses of global variables during initialization?

[Dipanjan Das via llvm-dev]

My objective is to instrument a module such that the addresses of all
global variables are printed out BEFORE even any real code is executed,
i.e. during module initialization. I slipped in the following code snippet
in the doIntialization() method of a FunctionPass. Unfortunately, I can't
see any code inserted in the IR generated.

====================================================================

bool doInitialization(Module &M) override {
        for (auto &global : M.getGlobalList()) {
            if (isa<GlobalVariable>(global)) {
                errs() << "[global]: " << global << '\n';
                auto &Ctx = M.getContext();
                IRBuilder<> builder(Ctx);
                Constant *instrument_func =
M.getOrInsertFunction("instrument_global_variable", Type::getVoidTy(Ctx),
Type::getInt64Ty(Ctx), NULL);
                Value* args[] = {global.getOperand(0)};
                builder.CreateCall(instrument_func, args);
            }
        }
    }

====================================================================

The code above yields a pass which, when executed against application
bitcode, prints out all the global variables (because of the errs()
statement) correctly. However, I can't collect the address information at
run-time.

-- 

Thanks & Regards,
Dipanjan
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