DllMain: hook games memset IAT to let us load in earlier

src/dllmain.cpp

@@ -1110,7 +1110,7 @@ void Miscellaneous()
     }
 }
 
-DWORD __stdcall Main(void*)
+void Main()
 {
     Logging();
     ReadConfig();
@@ -1122,7 +1122,27 @@ DWORD __stdcall Main(void*)
     AspectFOVFix();
     HUDFix();
     Miscellaneous();
-    return true; // end thread
+}
+
+std::mutex memsetHookMutex;
+bool memsetHookCalled = false;
+void* (__cdecl* memset_Fn)(void* Dst, int Val, size_t Size);
+void* __cdecl memset_Hook(void* Dst, int Val, size_t Size)
+{
+    // memset is one of the first imports called by game (not the very first though, since ASI loader still has those hooked during our DllMain...)
+    std::lock_guard lock(memsetHookMutex);
+    if(!memsetHookCalled)
+    {
+        memsetHookCalled = true;
+
+        // First we'll unhook the IAT for this function as early as we can
+        Memory::HookIAT(baseModule, "VCRUNTIME140.dll", memset_Hook, memset_Fn);
+
+    	// Apply our fixes before game has a chance to run
+    	Main();
+    }
+
+    return memset_Fn(Dst, Val, Size);
 }
 
 BOOL APIENTRY DllMain( HMODULE hModule,
@@ -1134,11 +1154,13 @@ BOOL APIENTRY DllMain( HMODULE hModule,
     {
     case DLL_PROCESS_ATTACH:
     {
-        HANDLE mainHandle = CreateThread(NULL, 0, Main, 0, NULL, 0);
-
-        if (mainHandle)
+        // Hook IAT of one of the imports game calls early on, so we can run our code in the same thread as the game before it has a chance to do anything
+        // This will only hook the main game modules usage of memset, other modules calling it won't be affected
+        HMODULE vcruntime140 = GetModuleHandleA("VCRUNTIME140.dll");
+        if (vcruntime140)
         {
-            CloseHandle(mainHandle);
+            memset_Fn = decltype(memset_Fn)(GetProcAddress(vcruntime140, "memset"));
+            Memory::HookIAT(baseModule, "VCRUNTIME140.dll", memset_Fn, memset_Hook);
         }
     }
     case DLL_THREAD_ATTACH:

src/helper.hpp

@@ -179,4 +179,41 @@ namespace Memory
     {
         return (address + 4 + *reinterpret_cast<std::int32_t*>(address));
     }
+
+    BOOL HookIAT(HMODULE callerModule, char const* targetModule, const void* targetFunction, void* detourFunction)
+    {
+        auto* base = (uint8_t*)callerModule;
+        const auto* dos_header = (IMAGE_DOS_HEADER*)base;
+        const auto nt_headers = (IMAGE_NT_HEADERS*)(base + dos_header->e_lfanew);
+        const auto* imports = (IMAGE_IMPORT_DESCRIPTOR*)(base + nt_headers->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT].VirtualAddress);
+
+        for (int i = 0; imports[i].Characteristics; i++)
+        {
+            const char* name = (const char*)(base + imports[i].Name);
+            if (lstrcmpiA(name, targetModule) != 0)
+                continue;
+
+            void** thunk = (void**)(base + imports[i].FirstThunk);
+
+            for (; *thunk; thunk++)
+            {
+                const void* import = *thunk;
+
+                if (import != targetFunction)
+                    continue;
+
+                DWORD oldState;
+                if (!VirtualProtect(thunk, sizeof(void*), PAGE_READWRITE, &oldState))
+                    return FALSE;
+
+                *thunk = detourFunction;
+
+                VirtualProtect(thunk, sizeof(void*), oldState, &oldState);
+
+                return TRUE;
+            }
+        }
+
+        return FALSE;
+    }
 }

src/stdafx.h

@@ -11,6 +11,7 @@
 #include <string>
 #include <iostream>
 #include <inttypes.h>
+#include <mutex>
 
 #include "external/loguru/loguru.hpp"
 #include "external/inipp/inipp/inipp.h"