sjithook's Introduction

SJITHook

Simple JIT compiler hook in C#.

Compatibility

It supports both x64 and x86 applications, and supports .NET version from 2.0 to 4.5

How to use

Add a reference to either SJITHook or SJITHook.Compact
Determine what .NET version the target assembly is using, and pass the according VTableAddrProvider to JITHook:

    // .NET 2.0->3.5
    var hook = new JITHook<MscorjitAddrProvider>();
    // .NET 4.0->4.5
    var hook = new JITHook<ClrjitAddrProvider>();

Install the hook, and pass your custom CompileMethod delegate:

    if (hook.Hook(HookedCompileMethod))
        Console.WriteLine("Successfully installed hook!");
            
    private static unsafe int HookedCompileMethod(IntPtr thisPtr, [In] IntPtr corJitInfo,
            [In] Data.CorMethodInfo* methodInfo, Data.CorJitFlag flags,
            [Out] IntPtr nativeEntry, [Out] IntPtr nativeSizeOfCode)
        {
            /*
                Do whatever you want with the parameters here
            */
            return hook.OriginalCompileMethod(thisPtr, corJitInfo, methodInfo, flags, nativeEntry, nativeSizeOfCode);
        }

Finally uninstall the hook when you're done using it:

    if (hook.UnHook())
        Console.WriteLine("Successfully uninstalled hook!");

Remarks

SJITHook is simply replacing the entry in CILJit's VTable, and not writing any instructions in the actual compileMethod function.
You need to enable Unsafe code in your project in order to use SJITHook.

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