Getting error 127 when calling GetProcAddress - windows

Question

I am writing a global hook for WH_GETMESSAGE. But I am getting the error code 127 i.e.,ERROR_PROC_NOT_FOUND, when calling the GetProcAddress function from the dll. Its unable to find the GetMsgProc. Any idea why?
Also, I am new to this kind of programming, so apologies for any mistake that's not expected.
DLL File:
#include "windows.h"
#include <stdio.h>
BOOL APIENTRY DllMain(HANDLE hModule, DWORD ul_reason_for_call, LPVOID lpReserved)
{
return TRUE;
}
__declspec(dllexport) LRESULT CALLBACK GetMsgProc(int nCode, WPARAM wParam, LPARAM lParam)
{
MessageBox(NULL, TEXT("I am in"),TEXT("In a DLL"), MB_OK);
return CallNextHookEx(NULL, nCode, wParam, lParam);
}
Program Loading the DLL file:
#include <windows.h>
#include <tchar.h>
#include <stdio.h>
typedef LRESULT(CALLBACK *LPGetMsgProc)(int nCode, WPARAM wParam, LPARAM lParam);
int main()
{
HMODULE hDll = LoadLibrary(_T("../../dllTouchInputHook/x64/Debug/dllTouchInputHook.dll"));
LPGetMsgProc proc = (LPGetMsgProc)GetProcAddress(hDll, "GetMsgProc");
if (proc == NULL) {
printf("The error code is %d", GetLastError());
}
HHOOK hMsgHook = SetWindowsHookEx(WH_GETMESSAGE, proc, hDll, 0);
MSG msg;
while (GetMessage(&msg, NULL, 0, 0) > 0) {
TranslateMessage(&msg);
DispatchMessage(&msg);
}
UnhookWindowsHookEx(hMsgHook);
return 0;
}

Answer 1

The function is not being found because it is not being exported as "GetMsgProc" like you are expecting. It is actually being exported more like "_GetMsgProc#12" (32bit) or "_GetMsgProc#20" (64bit) instead. If you want it exported as "GetMsgProc" then you need to use a .DEF file when compiling the DLL.
You shouldn't be implementing the hook in this manner to begin with. You should move the call to SetWindowsHookEx() inside the DLL itself, and then export a function to call it, eg:
#include "windows.h"
#include <stdio.h>
HINSTANCE hThisDLL;
HHOOK hMsgHook;
BOOL APIENTRY DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved)
{
hThisDLL = hinstDLL;
return TRUE;
}
LRESULT CALLBACK GetMsgProc(int nCode, WPARAM wParam, LPARAM lParam)
{
MessageBox(NULL, TEXT("I am in"), TEXT("In a DLL"), MB_OK);
return CallNextHookEx(NULL, nCode, wParam, lParam);
}
__declspec(dllexport) BOOL WINAPI InstallHook()
{
if (!hMsgHook)
hMsgHook = SetWindowsHookEx(WH_GETMESSAGE, &GetMsgProc, hThisDll, 0);
return (hMsgHook != NULL);
}
__declspec(dllexport) VOID WINAPI UninstallHook()
{
if (hMsgHook)
{
UnhookWindowsHookEx(hMsgHook);
hMsgHook = NULL;
}
}
#include <windows.h>
#include <tchar.h>
#include <stdio.h>
typedef BOOL (WINAPI *LPInstallHook)();
typedef VOID (WINAPI *LPUninstallHook)();
int main()
{
HMODULE hDll = LoadLibrary(_T("../../dllTouchInputHook/x64/Debug/dllTouchInputHook.dll"));
if (!hDll)
{
printf("The error code is %d", GetLastError());
return -1;
}
LPInstallHook installProc = (LPInstallHook) GetProcAddress(hDll, "InstallHook"); // or "_InstallHook"
LPUninstallHook uninstallProc = (installProc) ? (LPUninstallHook) GetProcAddress(hDll, "UninstallHook") : NULL; // or "_UninstallHook"
if (!(installProc && uninstallProc))
{
printf("The error code is %d", GetLastError());
FreeLibrary(hDll);
return -1;
}
if (!installProc())
{
printf("The error code is %d", GetLastError());
FreeLibrary(hDll);
return -1;
}
MSG msg;
while (GetMessage(&msg, NULL, 0, 0) > 0) {
TranslateMessage(&msg);
DispatchMessage(&msg);
}
uninstallProc();
FreeLibrary(hDll);
return 0;
}