isle/tools

LEGO Island Decompilation Tools

Accuracy to the game's original code is the main goal of this project. To facilitate the decompilation effort and maintain overall quality, we have devised a set of annotations, to be embedded in the source code, which allow us to automatically verify the accuracy of re-compiled functions' assembly, virtual tables, variable offsets and more.

In order for contributions to be accepted, the annotations must be used in accordance to the rules outlined here. Proper use is enforced by GitHub Actions which run the Python tools found in this folder. It is recommended to integrate these tools into your local development workflow as well.

Overview

We are continually working on extending the capabilities of our "decompilation language" and the toolset around it. Some of the following annotations have not made it into formal verification and thus are not technically enforced on the source code level yet (marked as WIP). Nevertheless, it is recommended to use them since it is highly likely they will eventually be fully integrated.

Functions

All non-inlined functions in the code base with the exception of 3rd party code must be annotated with one of the following markers, which include the module name and address of the function as found in the original binaries. This information is then used to compare the recompiled assembly with the original assembly, resulting in an accuracy score. Functions in a given compilation unit must be ordered by their address in ascending order.

The annotations can be attached to the function implementation, which is the most common case, or use the "comment" syntax (see examples below) for functions that cannot be referred to directly (such as templated, synthetic or non-inlined inline functions). The latter should only ever appear in .h files.

FUNCTION

Functions with a reasonably complete implementation which are not templated or synthetic (see below) should be annotated with FUNCTION.

// FUNCTION: LEGO1 0x100b12c0
MxCore* MxObjectFactory::Create(const char* p_name)
{
  // implementation
}

// FUNCTION: LEGO1 0x100140d0
// MxCore::IsA

STUB

Functions with no or a very incomplete implementation should be annotated with STUB. These will not be compared to the original assembly.

// STUB: LEGO1 0x10011d50
LegoCameraController::LegoCameraController()
{
  // TODO
}

TEMPLATE

Templated functions should be annotated with TEMPLATE. Since the goal is to eventually have a full accounting of all the functions present in the binaries, please make an effort to find and annotate every function of a templated class.

// TEMPLATE: LEGO1 0x100c0ee0
// list<MxNextActionDataStart *,allocator<MxNextActionDataStart *> >::_Buynode

// TEMPLATE: LEGO1 0x100c0fc0
// MxStreamListMxDSSubscriber::~MxStreamListMxDSSubscriber

// TEMPLATE: LEGO1 0x100c1010
// MxStreamListMxDSAction::~MxStreamListMxDSAction

SYNTHETIC

Synthetic functions should be annotated with SYNTHETIC. A synthetic function is generated by the compiler; most common is the "scalar deleting destructor" found in virtual tables. Other cases include default destructors and assignment operators. Note: SYNTHETIC takes precedence over TEMPLATE.

// SYNTHETIC: LEGO1 0x10003210
// Helicopter::`scalar deleting destructor'

// SYNTHETIC: LEGO1 0x100c4f50
// MxCollection<MxRegionLeftRight *>::`scalar deleting destructor'

// SYNTHETIC: LEGO1 0x100c4fc0
// MxList<MxRegionLeftRight *>::`scalar deleting destructor'

LIBRARY

Functions located in 3rd party libraries should be annotated with LIBRARY. Since the goal is to eventually have a full accounting of all the functions present in the binaries, please make an effort to find and annotate every function of every statically linked library, including the MSVC standard libraries.

// LIBRARY: ISLE 0x4061b0
// _MemPoolInit@4

// LIBRARY: ISLE 0x406520
// _MemPoolSetPageSize@8

// LIBRARY: ISLE 0x406630
// _MemPoolSetBlockSizeFS@8

Virtual tables

Classes with a virtual table should be annotated using the VTABLE marker, which includes the module name and address of the virtual table. Additionally, virtual function declarations should be annotated with a comment indicating their relative offset. Please use the following example as a reference.

// VTABLE: LEGO1 0x100dc900
class MxEventManager : public MxMediaManager {
public:
	MxEventManager();
	virtual ~MxEventManager() override;

	virtual void Destroy() override;                                     // vtable+0x18
	virtual MxResult Create(MxU32 p_frequencyMS, MxBool p_createThread); // vtable+0x28

Class size (WIP)

Classes should be annotated using the SIZE marker to indicate their size. If you are unsure about the class size in the original binary, please use the currently available information (known member variables) and detail the circumstances in an extra comment if necessary.

// SIZE 0x1c
class MxCriticalSection {
public:
	MxCriticalSection();
	~MxCriticalSection();
	static void SetDoMutex();

Member variables (WIP)

Member variables should be annotated with their relative offsets.

class MxDSObject : public MxCore {
private:
	MxU32 m_sizeOnDisk;   // 0x8
	MxU16 m_type;         // 0xc
	char* m_sourceName;   // 0x10
	undefined4 m_unk0x14; // 0x14

Global variables

Global variables should be annotated using the GLOBAL marker, which includes the module name and address of the variable.

// GLOBAL: LEGO1 0x100f456c
MxAtomId* g_jukeboxScript = NULL;

// GLOBAL: LEGO1 0x100f4570
MxAtomId* g_pz5Script = NULL;

// GLOBAL: LEGO1 0x100f4574
MxAtomId* g_introScript = NULL;

Strings

String values should be annotated using the STRING marker, which includes the module name and address of the string.

inline virtual const char* ClassName() const override // vtable+0x0c
{
	// STRING: LEGO1 0x100f03fc
	return "Act2PoliceStation";
}

Tooling

Use pip to install the required packages to be able to use the Python tools found in this folder:

pip install -r tools/requirements.txt

• patch_c2.py: Patches C2.EXE (part of MSVC 4.20), to get rid of a bugged warning
• reccmp: Compares the original EXE or DLL with a recompiled EXE or DLL, provided a PDB file
• verexp: Verifies exports by comparing the exports of the original DLL and the recompiled DLL
• decomplint: Checks the decompilation annotations (see above)
• ncc: Checks naming conventions based on a set of rules
• isledecomp: A library that implements a parser to identify the "decompilation" annotations (see above)

Testing

isledecomp has a small suite of tests. Install pylint and run it, passing in the directory:

pip install pytest
pytest tools/isledecomp/tests/

Development

In order to keep the code clean and consistent, we use pylint and black:

pip install black pylint

Run pylint (ignores build and virtualenv)

pylint tools/ --ignore=build,bin,lib

Check code formatting without rewriting files

black --check tools/

Apply code formatting

black tools/