San Andreas Multiplayer

This is an ongoing work-in-progress decompilation of the latest version of San Andreas Multiplayer (SA-MP), a free Massively Multiplayer Online game mod for the PC version of Rockstar Games Grand Theft Auto: San Andreas.

The project aims to be a matching decompilation. Meaning, producing a source code base that, when it's recompiled with the same compiler the original developers used, outputs the exact same binary as the original one.

Decompiling and extracting the containing binaries from the following version packages:

Status values may not be 100% accurate and will fluctuate during the analyzation of the binary files. These numbers currently are based on the number of functions marked in light green color and the number of visible functions in the IDA Pro database, and this does not represent the overall byte-for-byte accuracy of the output file with the original one.

The client library is built with Microsoft Visual C++ 7.1 (cl.exe 13.10.3077), the compiler that ships with Visual Studio .NET 2003. This is not a preference. A matching decompilation only reproduces the original bytes if the original compiler produces them, and no later MSVC release generates the same code for this source. Building with a modern toolset may well succeed and will not match.

Two flags worth knowing before you start: /GS- does not exist in VC7.1 (buffer security checks are off by default, and BufferSecurityCheck="FALSE" in the project reflects that), and __thiscall is not a usable keyword in this compiler version.

Open saco.sln in Visual Studio .NET 2003 and build the Release configuration of the saco project. The output is saco/Release/samp.dll. The Debug configuration exists but produces nothing comparable to the original binary.

Other components have their own solutions: announce/announce.sln, arctool2/arctool2.sln, bot/bot.sln and server/server.sln.

VC7.1 runs well under Wine. Install Visual Studio .NET 2003 into a Wine prefix, then invoke cl.exe directly. Two things are easy to get wrong: the working directory has to be saco/, and INCLUDE has to be set explicitly, because the Wine environment does not inherit the compiler's own registry settings.

export WINEPREFIX="$HOME/.wine"
VC='C:\Program Files\Microsoft Visual Studio .NET 2003\Vc7'
export INCLUDE="$VC\\include;$VC\\PlatformSDK\\Include"
cd saco
wine "$VC\\bin\\cl.exe" /c /Ox /Og /Ob1 /Oi /Ot /Oy /MT /Zp1 /EHsc /GF \
 /D WIN32 /D NDEBUG /D _WINDOWS /D _USRDLL /D SACO_EXPORTS /D SAMPCLI \
 /I "d3d9\\include" /I "." net\\netgame.cpp /Fo"Z:\\tmp\\netgame.obj"

These are the settings the Release configuration in saco/saco.vcproj expands to. They matter because changing any of them changes the generated code, so a function that matched before may stop matching.

Preprocessor definitions are WIN32, NDEBUG, _WINDOWS, _USRDLL, SACO_EXPORTS and SAMPCLI, and the only additional include directory is d3d9\include.

Five files carry per-file overrides, and compiling them with the defaults above will not match:

The link is /SUBSYSTEM:WINDOWS /MACHINE:X86 against dxguid.lib, d3d9.lib, d3dx9.lib, comctl32.lib, wsock32.lib, winmm.lib and bass.lib, with d3d9 as an additional library directory. Both /OPT:NOREF and /OPT:NOICF are in effect (OptimizeReferences="0" and EnableCOMDATFolding="0"), so the linker neither strips unreferenced functions nor folds identical ones. Identical functions therefore appear separately in the original binary, which is why byte-identical siblings are expected rather than suspicious.

samp.dll does not link yet. raknet/SocketDataEncryptor.cpp is referenced by the project but is not present in the tree, and it is the only such file. Every other translation unit the project lists compiles cleanly.

Because of that, progress is measured per function rather than per binary. A function counts as done when the bytes the compiler emits for it are identical to the bytes at the corresponding address in the original samp.dll, after masking the four-byte slots that COFF marks as relocations. Masking is what makes an unlinked object file comparable to a linked binary: call targets, global addresses and string addresses are resolved at link time and cannot agree, while every other byte must.