Cvars: Hook Cvar_DirectSet from engine library

amxmodx/cvars.cpp

@@ -0,0 +1,70 @@
+// vim: set ts=4 sw=4 tw=99 noet:
+//
+// AMX Mod X, based on AMX Mod by Aleksander Naszko ("OLO").
+// Copyright (C) The AMX Mod X Development Team.
+//
+// This software is licensed under the GNU General Public License, version 3 or higher.
+// Additional exceptions apply. For full license details, see LICENSE.txt or visit:
+//     https://alliedmods.net/amxmodx-license
+
+#include "cvars.h"
+#include "amxmodx.h"
+#include <CDetour/detours.h>
+
+CDetour *Cvar_DirectSetDetour;
+
+DETOUR_DECL_STATIC2(Cvar_DirectSet, void, struct cvar_s*, var, const char*, value)
+{
+	printf("Cvar_DirectSet - %s -> %s\n", var->name, value);
+
+	DETOUR_STATIC_CALL(Cvar_DirectSet)(var, value);
+}
+
+void CreateCvarHook(void)
+{
+	// void PF_Cvar_DirectSet(struct cvar_s *var, const char *value) // = pfnCvar_DirectSet
+	// {
+	//   	Cvar_DirectSet(var, value); // <- We want to hook this.
+	// }
+
+	byte *baseAddress = (byte *)g_engfuncs.pfnCvar_DirectSet;
+	uintptr_t *functionAddress = nullptr;
+
+#if defined(WIN32)
+	// 55              push    ebp
+	// 8B EC           mov     ebp, esp
+	// 8B 45 0C        mov     eax, [ebp+arg_4]
+	// 8B 4D 08        mov     ecx, [ebp+arg_0]
+	// 50              push    eax
+	// 51              push    ecx
+	// E8 XX XX XX XX  call    Cvar_DirectSet
+	const byte opcodeJump = 0xE8;
+#else
+	// E9 XX XX XX XX  jmp     Cvar_DirectSet
+	const byte opcodeJump = 0xE9;
+#endif
+
+	const byte opcodeJumpSize     = 5;
+	const byte opcodeJumpByteSize = 1;
+
+	const int maxBytesLimit = 20;
+
+	for (size_t i = 0; i < maxBytesLimit; ++i, ++baseAddress)
+	{
+		if (*baseAddress == opcodeJump)
+		{
+			functionAddress = (uintptr_t *)(&baseAddress[opcodeJumpSize] + *(uintptr_t *)&baseAddress[opcodeJumpByteSize]);
+			break;
+		}
+	}
+
+	if (functionAddress)
+	{
+		CDetour *Cvar_DirectSetDetour = DETOUR_CREATE_STATIC_FIXED(Cvar_DirectSet, (void *)functionAddress);
+
+		if (Cvar_DirectSetDetour)
+		{
+			Cvar_DirectSetDetour->EnableDetour();
+		}
+	}
+}