Detours.cs

using System;
using System.Collections.Generic;
using System.Reflection;

namespace CommunityCoreLibrary
{
    
    public static class Detours
    {
        
        private static List<string> detoured = new List<string>();
        private static List<string> destinations = new List<string>();

        /**
            This is a basic first implementation of the IL method 'hooks' (detours) made possible by RawCode's work;
            https://ludeon.com/forums/index.php?topic=17143.0

            Performs detours, spits out basic logs and warns if a method is detoured multiple times.
        **/
        public static unsafe bool TryDetourFromTo ( MethodInfo source, MethodInfo destination )
        {
            // error out on null arguments
            if( source == null )
            {
                CCL_Log.Trace( Verbosity.FatalErrors,
                    "Source MethodInfo is null",
                    "Detours"
                );
                return false;
            }

            if( destination == null )
            {
                CCL_Log.Trace( Verbosity.FatalErrors,
                    "Destination MethodInfo is null",
                    "Detours"
                );
                return false;
            }

            // keep track of detours and spit out some messaging
            string sourceString      = source.DeclaringType.FullName      + "." + source.Name      + " @ 0x" + source.MethodHandle.GetFunctionPointer().ToString( "X" + ( IntPtr.Size *  2 ).ToString() );
            string destinationString = destination.DeclaringType.FullName + "." + destination.Name + " @ 0x" + destination.MethodHandle.GetFunctionPointer().ToString( "X" + ( IntPtr.Size *  2 ).ToString() );

#if DEBUG
            if( detoured.Contains( sourceString ) )
            {
                CCL_Log.Trace( Verbosity.Warnings,
                    "Source method ('" + sourceString + "') is previously detoured to '" + destinations[ detoured.IndexOf( sourceString ) ] + "'",
                    "Detours"
                );
            } 
            CCL_Log.Trace( Verbosity.Injections,
                "Detouring '" + sourceString + "' to '" + destinationString + "'",
                "Detours"
            );
#endif
            
            detoured.Add( sourceString );
            destinations.Add( destinationString );

            if( IntPtr.Size == sizeof( Int64 ) )
            {
                // 64-bit systems use 64-bit absolute address and jumps
                // 12 byte destructive

                // Get function pointers
                long Source_Base        = source     .MethodHandle.GetFunctionPointer().ToInt64();
                long Destination_Base   = destination.MethodHandle.GetFunctionPointer().ToInt64();

                // Native source address
                byte* Pointer_Raw_Source = (byte*)Source_Base;

                // Pointer to insert jump address into native code
                long* Pointer_Raw_Address = (long*)( Pointer_Raw_Source + 0x02 );

                // Insert 64-bit absolute jump into native code (address in rax)
                // mov rax, immediate64
                // jmp [rax]
                *( Pointer_Raw_Source + 0x00 ) = 0x48;
                *( Pointer_Raw_Source + 0x01 ) = 0xB8;
                *Pointer_Raw_Address           = Destination_Base; // ( Pointer_Raw_Source + 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09 )
                *( Pointer_Raw_Source + 0x0A ) = 0xFF;
                *( Pointer_Raw_Source + 0x0B ) = 0xE0;

            }
            else
            {
                // 32-bit systems use 32-bit relative offset and jump
                // 5 byte destructive

                // Get function pointers
                int Source_Base        = source     .MethodHandle.GetFunctionPointer().ToInt32();
                int Destination_Base   = destination.MethodHandle.GetFunctionPointer().ToInt32();

                // Native source address
                byte* Pointer_Raw_Source = (byte*)Source_Base;

                // Pointer to insert jump address into native code
                int* Pointer_Raw_Address = (int*)( Pointer_Raw_Source + 1 );

                // Jump offset (less instruction size)
                int offset = ( Destination_Base - Source_Base ) - 5;

                // Insert 32-bit relative jump into native code
                *Pointer_Raw_Source = 0xE9;
                *Pointer_Raw_Address = offset;
            }

            // done!
            return true;
        }

    }

}