/// <summary>
/// Creates the wrapper function that wraps a native function with our own defined or custom calling convention,
/// into a regular X64 Microsoft Calling Convention function that is natively supported by the C# programming language.
///
/// This allows us to call non-standard "usercall" game functions, such as for example functions that take values
/// in registers as parameters instead of using the stack, functions which take paremeters in a mixture of both stack
/// and registers as well as functions which varying return parameters, either caller or callee cleaned up.
/// </summary>
/// <param name="functionAddress">The address of the function to create a wrapper for.</param>
/// <param name="reloadedFunction">Structure containing the details of the actual function in question.</param>
/// <returns>Pointer to the new X64 Microsoft Calling Convention function address to call from C# code to invoke our game function.</returns>
private static IntPtr CreateWrapperFunctionInternal <TFunction>(IntPtr functionAddress, X64ReloadedFunctionAttribute reloadedFunction)
{
// Retrieve number of parameters.
int numberOfParameters = FunctionCommon.GetNumberofParametersWithoutFloats(typeof(TFunction));
int nonRegisterParameters = numberOfParameters - reloadedFunction.SourceRegisters.Length;
// List of ASM Instructions to be Compiled
List <string> assemblyCode = new List <string> {
"use64"
};
// Backup Stack Frame
assemblyCode.Add("push rbp"); // Backup old call frame
assemblyCode.Add("mov rbp, rsp"); // Setup new call frame
// Setup Function Parameters
if (numberOfParameters > 0)
{
assemblyCode.AddRange(AssembleFunctionParameters(numberOfParameters, reloadedFunction.SourceRegisters));
}
// Make Shadow Space if necessary.
if (reloadedFunction.ShadowSpace)
{
assemblyCode.Add("sub rsp, 32"); // Setup new call frame
}
// Assemble the call to the game function in question.
assemblyCode.AddRange(HookCommon.X64AssembleAbsoluteCallMnemonics(functionAddress, reloadedFunction));
// Move return register back if necessary.
if (reloadedFunction.ReturnRegister != X64ReloadedFunctionAttribute.Register.rax)
{
assemblyCode.Add("mov rax, " + reloadedFunction.ReturnRegister);
}
// Restore the stack pointer from the Shadow Space
// 8 = IntPtr.Size
// 32 = Shadow Space
if (reloadedFunction.ShadowSpace)
{
assemblyCode.Add("add rsp, " + ((nonRegisterParameters * 8) + 32));
}
else
{
assemblyCode.Add("add rsp, " + (nonRegisterParameters * 8));
}
// Restore Stack Frame and Return
assemblyCode.Add("pop rbp");
assemblyCode.Add("ret");
// Write function to buffer and return pointer.
byte[] assembledMnemonics = Assembler.Assembler.Assemble(assemblyCode.ToArray());
return(MemoryBufferManager.Add(assembledMnemonics));
}
/// <summary>
/// Creates the wrapper function for redirecting program flow to our C# function.
/// </summary>
/// <param name="reloadedFunction">Structure containing the details of the actual function in question.</param>
/// <param name="functionAddress">The address of the function to create a wrapper for.</param>
/// <returns></returns>
internal static IntPtr CreateX64WrapperFunctionInternal <TFunction>(IntPtr functionAddress, X64ReloadedFunctionAttribute reloadedFunction)
{
// Retrieve number of parameters.
int numberOfParameters = FunctionCommon.GetNumberofParametersWithoutFloats(typeof(TFunction));
int nonRegisterParameters = numberOfParameters - reloadedFunction.SourceRegisters.Length;
// List of ASM Instructions to be Compiled
List <string> assemblyCode = new List <string> {
"use64"
};
// If the attribute is Microsoft Call Convention, take fast path!
if (reloadedFunction.Equals(new X64ReloadedFunctionAttribute(X64CallingConventions.Microsoft)))
{
// Backup old call frame
assemblyCode.AddRange(HookCommon.X64AssembleAbsoluteJumpMnemonics(functionAddress, reloadedFunction));
}
else
{
// Backup Stack Frame
assemblyCode.Add("push rbp"); // Backup old call frame
assemblyCode.Add("mov rbp, rsp"); // Setup new call frame
// We assume that we are stack aligned in usercall/custom calling conventions, if we are not, game over for now.
// Our stack frame alignment is off by 8 here, we must also consider non-register parameters.
// Note to self: In the case you forget, dummy. Your stack needs to be 16 byte aligned.
// Calculate the bytes our wrapper parameters take on the stack in total.
// The stack frame backup, push rbp and CALL negate themselves so it's down to this.
// Then our misalignment to the stack.
int stackBytesTotal = (nonRegisterParameters * 8);
int stackMisalignment = (stackBytesTotal % 16);
// Prealign stack
assemblyCode.Add($"sub rbp, {stackMisalignment}"); // Setup new call frame
// Setup the registers for our C# method.
assemblyCode.AddRange(AssembleFunctionParameters(numberOfParameters, reloadedFunction, stackMisalignment));
// And now we add the shadow space for C# method's Microsoft Call Convention.
assemblyCode.Add("sub rsp, 32"); // Setup new call frame
// Assemble the Call to C# Function Pointer.
assemblyCode.AddRange(HookCommon.X64AssembleAbsoluteCallMnemonics(functionAddress, reloadedFunction));
// MOV our own return register, EAX into the register expected by the calling convention
assemblyCode.Add($"mov {reloadedFunction.ReturnRegister}, rax");
// Restore stack pointer (this is always the same, our function is Microsoft Call Convention Compliant)
assemblyCode.Add("add rsp, " + ((nonRegisterParameters * 8) + 32));
// Restore stack alignment
assemblyCode.Add($"add rbp, {stackMisalignment}");
// Restore Stack Frame and Return
assemblyCode.Add("pop rbp");
assemblyCode.Add("ret");
}
// Assemble and return pointer to code
byte[] assembledMnemonics = Assembler.Assembler.Assemble(assemblyCode.ToArray());
return(MemoryBufferManager.Add(assembledMnemonics));
}
