How to Load External DLL from Dissector

Question

I have a DLL file named, Test2.dll which loads fine in anything but wireshark, but when I try to open it within my wireshark dissector it fails to load, this is how I am loading it:

#define LIBRARYLOCATION "C:\\Docum...\\Test2.dll"
…
static void dissect_foo(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree){
HINSTANCE DLLInstance = LoadLibrary((LPCWSTR)LIBRARYLOCATION);
if(DLLInstance == NULL){
proto_tree_add_text(tree, NULL, 0, 0, "Cannot Load DLL: %*s", 0, LIBRARYLOCATION);}
else{
proto_tree_add_text(tree, NULL, 0, 0, "Loaded DLL: %*s", 0, LIBRARYLOCATION);}

The .h file for the DLL is thus:

#ifndef TEST2_H
#define TEST2_H
#ifdef __cplusplus
extern "C"
{
#endif
__declspec(dllexport) void Foo ();
#ifdef __cplusplus
}
#endif
#endif

Any ideas as to why this wouldn’t work? The DLL is compiled in VC++ 2005 (No option there) and the dissector is compiled with VC++ 2010 EE.

Thank you for your time, Brandon

Answer 1

Bug: You're passing a single-char string as a wide-char string to LoadLibrary, but you actually need to pass in a TCHAR string (which is set at compile-time to be either wide-char or single-char).

Fix: Use _T for the literal #define, and remove the LPCWSTR cast (presumably done to mute the compiler warning you should've heeded).

from:

#define LIBRARYLOCATION "C:\\Docum...\\Test2.dll"
/* ... */
HINSTANCE DLLInstance = LoadLibrary((LPCWSTR)LIBRARYLOCATION);

to:

//#include <tchar.h>
#define LIBRARYLOCATION _T("C:\\Docum...\\Test2.dll")
/* ... */
HINSTANCE DLLInstance = LoadLibrary(LIBRARYLOCATION);