Hooking function with C++, IDA and .pdb file

Question

I want to call a function in a program. I do this from a DLL entry point. I opened the program in IDA together with its .pdb file. This is what the function looks like according to IDA:

void __fastcall Logger::log(LogLevel lvl, const char *msg)

(LogLevel is just an enum)

The parameters are obvious and not the problem.

But the problem is that I propably have the wrong address of it (I assume I need to get the address of the class first?) IDA gave me:

.text:00000001400981A0

for the function. This is what I tried:

BOOL WINAPI DllMain(HINSTANCE hModule, DWORD dwReason, LPVOID lpReserved) {
  if (dwReason == DLL_PROCESS_ATTACH) {
    typedef void __fastcall func(int lvl, const char* msg);
    func* loggerLog = (func*)(GetModuleHandle(0) + 0x1400981A0);
    loggerLog(0, "test 123");
  }
  return 1;
}

Doing this the program just closes, no error.

I'm not sure where to start. What is the correct way and address? How would I get the address I need?

Answer 1

0x1400981A0 - this was a wrong valuee to add. Most likely you need to use GetModuleHandle(0) + 0x981A0. Because GetModuleHandle(0) will give you the base address like 0x140000000. I.e. IDA shows you the virtual address to which DLL would be loaded if OS has the address available. In other cases you need to know RVA (relative virtual address), so that you calculate the address of the function like RVA + virtual address to which OS loaded the DLL.