llvm dev - May 2017 - How to instrument a module to spit out the addresses of global variables during initialization?

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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To be precise, I am not being able to insert any
appropriate builder.SetInsertPoint() call inside doInitialization() method.

On 3 May 2017 at 14:58, Dipanjan Das <mail.dipanjan.das at gmail.com>
wrote:
>
> 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
>


-- 

Thanks & Regards,
Dipanjan
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