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omath::unreal_engine object array — walking GObjects

Header: omath/engines/unreal_engine/object_array.hpp Namespace: omath::unreal_engine Purpose: enumerate the global UObject array on UE 2.5, UE 3, UE 4 and UE 5

Summary

template<rev_eng::MemoryReadTrait MemoryTrait = rev_eng::InternalMemoryTrait>
std::expected<std::uint32_t, ObjectArrayError>
get_object_count(std::uintptr_t g_objects, const ObjectArrayLayout& layout);

template<rev_eng::MemoryReadTrait MemoryTrait = rev_eng::InternalMemoryTrait>
std::expected<std::uintptr_t, ObjectArrayError>
get_object_by_index(std::uintptr_t g_objects, std::uint32_t index, const ObjectArrayLayout& layout);

get_object_by_index bounds checks the index against the stored count, walks the array and returns the UObject address, which is exactly what get_actor_name expects.

g_objects is the address of UObject::GObjObjects on UE 2.5 and UE 3, and the address of GUObjectArray on UE 4 and UE 5.

Generation ObjectArrayKind Container
UE 2.5, UE 3 FLAT TArray<UObject*>
UE 4 with a fixed array FLAT FFixedUObjectArray, elements are FUObjectItem
UE 4.11+, UE 5 CHUNKED FChunkedFixedUObjectArray, 64K FUObjectItem per chunk
UE 4.0 - 4.10 CHUNKED with indirect_chunk_table = false chunk table inlined into the array object

Iterating

#include <omath/engines/unreal_engine/actor_name.hpp>
#include <omath/engines/unreal_engine/object_array.hpp>

using namespace omath::unreal_engine;

void dump_objects(const std::uintptr_t g_objects, const std::uintptr_t g_names)
{
    const auto count = get_object_count(g_objects, ObjectArrayLayout::ue5());

    if (!count.has_value())
        return;

    for (std::uint32_t i = 0; i < *count; ++i)
    {
        const auto object = get_object_by_index(g_objects, i, ObjectArrayLayout::ue5());

        // Slots of destroyed objects are empty, skipping them is normal
        if (!object.has_value())
            continue;

        const auto name = get_actor_name(*object, g_names, NameLayout::ue5());

        if (name.has_value())
            std::println("[{}] {:#x} {}", i, *object, *name);
    }
}

Presets

ObjectArrayLayout::ue2_5();     // UE 2.5, x86, TArray<UObject*>
ObjectArrayLayout::ue3();       // UE 3, x86, same TArray<UObject*>
ObjectArrayLayout::ue4_fixed(); // UE 4 with FFixedUObjectArray, x64
ObjectArrayLayout::ue4();       // UE 4.11+, x64, FChunkedFixedUObjectArray
ObjectArrayLayout::ue5();       // same layout as ue4()

Presets hold the values that are typical for their generation, they are not guaranteed for your game. Common overrides:

auto layout = ObjectArrayLayout::ue5();
layout.item_stride = 0x20;             // FUObjectItem grew in this build
layout.count_offset = 0x2C;            // FUObjectArray header differs

auto early = ObjectArrayLayout::ue4(); // UE 4.0 - 4.10
early.indirect_chunk_table = false;    // chunk table is inlined, not behind a pointer
early.elements_per_chunk = 16384;
early.item_stride = sizeof(std::uintptr_t); // chunks hold bare UObject*, no FUObjectItem

auto ue3 = ObjectArrayLayout::ue3();   // 64 bit tool reading a 32 bit game
ue3.pointer_size = sizeof(std::uint32_t);
ue3.item_stride = sizeof(std::uint32_t);

Errors

ObjectArrayError Meaning
NULL_POINTER g_objects is zero, or the array/chunk pointer behind it is zero
INDEX_OUT_OF_RANGE index is not below the stored element count
NULL_OBJECT the slot is empty, its object was destroyed