/// <summary>
/// Allows you to insert a set of your own assembly instructions in the middle of a game function and have the game conditionally redirect
/// to said function.
///
/// The hook requires a minimum of 6 (X86) or 7 (X64) bytes and will therefore overwrite as many instructions as it needs until it can get enough space
/// to place the hook. If you have ever used Cheat ENgine's assembly injection, you're already familliar on how to work with this class.
/// </summary>
/// <param name="hookAddress">
/// The memory address for which the hook is to be generated.
/// </param>
/// <param name="mnemonics">
/// X86-32 or X64 FASM compatible assembly code that starts with the line use16, use32 or use64 for identifying the architecture.
/// </param>
/// <param name="originalInstructionOptions">
/// Defines a switch for the assembly hook builder telling it what should be done with the original set of bytes that are going to be
/// replaced with the jump opcode.
/// </param>
/// <param name="hookLength">[Optional] The explicit amount of bytes to overwrite when inserting the actual hook.</param>
public AssemblyHook(IntPtr hookAddress, string[] mnemonics, OriginalInstructionOptions originalInstructionOptions, int hookLength = -1)
{
// Set hook address.
HookAddress = hookAddress;
// Our 32bit and 64bit code paths will differ once we get the disassembler rolling.
bool is64bit = mnemonics[0] == "use64";
// Get the default for architecture, then true hook length.
if (hookLength == -1)
{
hookLength = GetDefaultHookLength(is64bit);
ArchitectureMode disassemblerMode = is64bit ? ArchitectureMode.x86_64 : ArchitectureMode.x86_32;
hookLength = HookCommon.GetHookLength(HookAddress, hookLength, disassemblerMode);
}
// Assemble our custom ASM hook function to be jumped to and executed by the game, then write it to memory.
IntPtr returnAddress = HookAddress + hookLength;
byte[] assembledBytes = Assembler.Assembler.Assemble(mnemonics);
assembledBytes = ProcessCustomInstructions(assembledBytes, OriginalBytes, originalInstructionOptions);
assembledBytes = AppendJumpBack(assembledBytes, is64bit, returnAddress);
AsmHookAddress = MemoryBufferManager.Add(assembledBytes);
// Backup our bytes to hook.
OriginalBytes = Bindings.TargetProcess.ReadMemory(HookAddress, hookLength);
// Setup our new bytes to overwrite the old ones with (absolute jump).
NewBytes = new byte[hookLength];
Populate(NewBytes, (byte)0x90); // NOP
byte[] hookJump = AssembleJump(is64bit, AsmHookAddress); // Assemble absolute jump and copy to array of NOPs.
Array.Copy(hookJump, NewBytes, hookJump.Length);
}
/// <summary>
/// Assembles an absolute jump either from the end of the hook back, or to the hook.
/// </summary>
/// <param name="is64Bit">Set to true to assemble a 64bit jump, else 32bit.</param>
/// <param name="jumpAddress">The address to jump to.</param>
/// <returns>An bytes for an absolute jump back to the end of the hook.</returns>
private byte[] AssembleJump(bool is64Bit, IntPtr jumpAddress)
{
return(is64Bit ?
HookCommon.X64AssembleAbsoluteJump(jumpAddress, new X64ReloadedFunctionAttribute(X64CallingConventions.Microsoft)):
HookCommon.X86AssembleAbsoluteJump(jumpAddress));
}
/// <summary>
/// Assembles a dummy jump to an absolute address in order to get the length of an absolute jump under
/// X86/X64.
/// </summary>
/// <param name="is64Bit">Set to true to calculate a 64bit absolute jump length.</param>
/// <returns></returns>
private int GetDefaultHookLength(bool is64Bit)
{
return(is64Bit ?
HookCommon.X64AssembleAbsoluteJump((IntPtr)0x11223344, new X64ReloadedFunctionAttribute(X64CallingConventions.Microsoft)).Length :
HookCommon.X86AssembleAbsoluteJump((IntPtr)0x11223344).Length);
}
