From 7868f363128373048c429dfbe39492db9b2ca8a8 Mon Sep 17 00:00:00 2001
From: Maurice Heumann <mauriceheumann@gmail.com>
Date: Mon, 17 May 2021 22:40:32 +0200
Subject: [PATCH] Support getting v-table entries

---
 src/common/utils/hook.hpp | 49 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/src/common/utils/hook.hpp b/src/common/utils/hook.hpp
index 251131e..bb24f8c 100644
--- a/src/common/utils/hook.hpp
+++ b/src/common/utils/hook.hpp
@@ -8,6 +8,55 @@ using namespace asmjit::x86;
 
 namespace utils::hook
 {
+	namespace detail
+	{
+		template<size_t entries>
+		std::vector<size_t(*)()> get_iota_functions()
+		{
+			if constexpr (entries == 0)
+			{
+				std::vector<size_t(*)()> functions;
+				return functions;
+			}
+			else
+			{
+				auto functions = get_iota_functions<entries - 1>();
+				functions.emplace_back([]()
+				{
+					return entries - 1;
+				});
+				return functions;
+			}
+		}
+	}
+
+	// Gets the pointer to the entry in the v-table.
+	// It seems otherwise impossible to get this.
+	// This is ugly as fuck and only safely works on x64
+	// Example:
+	//   ID3D11Device* device = ...
+	//   auto entry = get_vtable_entry(device, &ID3D11Device::CreateTexture2D);
+	template <size_t entries = 100, typename Class, typename T, typename... Args>
+	void** get_vtable_entry(Class* obj, T (Class::* entry)(Args ...))
+	{
+		union
+		{
+			decltype(entry) func;
+			void* pointer;
+		};
+
+		func = entry;
+
+		auto iota_functions = detail::get_iota_functions<entries>();
+		auto* object = iota_functions.data();
+
+		using FakeFunc = size_t(__thiscall*)(void* self);
+		auto index = static_cast<FakeFunc>(pointer)(&object);
+
+		void** obj_v_table = *reinterpret_cast<void***>(obj);
+		return &obj_v_table[index];
+	}
+
 	class assembler : public Assembler
 	{
 	public: