llvm dev - Jul 2018 - how to convert value to size_t

Hi,

I am instrumenting load and store and passing memory address to the instrumented
function like below -

 	Type* void_ptr_ty = PointerType::getUnqual(Type::getInt8Ty(M.getContext()));
 	RecordMem = M.getOrInsertFunction("RecordMem", VoidTy, size_ty,
void_ptr_ty);

 	bool IsWrite = isa<StoreInst>(*I);
  	Value *Addr = IsWrite
      		? cast<StoreInst>(I)->getPointerOperand()
      		: cast<LoadInst>(I)->getPointerOperand();

 	BitCastInst* bitcast = new BitCastInst(Addr,
           PointerType::getUnqual(Type::getInt8Ty(M.getContext())),
             "", I); 
 
  	ArgsV.push_back(bitcast);
 
  	IRB.CreateCall(RecordMem, ArgsV);

and in function RecordMem, I am type casting void Addr to size_t - 

	extern "C" void RecordMem(THREADID threadid, void * addr) {
  		size_t addr_addr = (size_t)addr;
		…
	}

I don’t want to type cast to size_t in RecordMem. I want to pass it as size_t
from llvm pass.

My RecordMem interface now is - 

		extern "C" void RecordMem(THREADID threadid, size_t addr) {}

How can I achieve this? How can I pass the address as size_t?




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Hi Sangeeta,

On Tue, 17 Jul 2018 at 05:00, sangeeta chowdhary via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> How can I achieve this? How can I pass the address as size_t?
You have to know what size_t maps to for your platform and then use a
PtrToInt instruction to cast it to that instead of i8*. LLVM doesn't
store this information anywhere, but the answer is usually the same as
the pointer size (which you could obtain from the Module's
DataLayout).

Though to my mind passing a "void *" is more descriptive anyway, or
maybe a uintptr_t at a stretch.

Cheers.

Tim.