internal MethodRedirection(MethodBase original, MethodBase replacement, bool start)
{
Original = original;
Replacement = replacement;
// Note: I'm making local copies of the following fields to avoid accessing fields multiple times.
RuntimeMethodHandle originalHandle = original.GetRuntimeMethodHandle();
RuntimeMethodHandle replacementHandle = replacement.GetRuntimeMethodHandle();
const string JIT_ERROR = "The specified method hasn't been jitted yet, and thus cannot be used in a redirection.";
// Fetch their respective start
IntPtr originalStart = originalHandle.GetMethodStart();
IntPtr replacementStart = replacementHandle.GetMethodStart();
// Edge case: calling this on the same method
if (originalStart == replacementStart)
{
throw new InvalidOperationException("Cannot redirect a method to itself.");
}
// Edge case: methods are too close to one another
int difference = (int)Math.Abs(originalStart.ToInt64() - replacementStart.ToInt64());
int sizeOfPtr = IntPtr.Size;
if (difference <= Helpers.PatchSize)
{
throw new InvalidOperationException("Unable to redirect methods whose bodies are too close to one another.");
}
// Make sure they're jitted
if (!originalStart.HasBeenCompiled())
{
if (!Helpers.TryPrepareMethod(original, originalHandle))
{
throw new ArgumentException(JIT_ERROR, nameof(original));
}
originalStart = originalHandle.GetMethodStart();
}
if (!replacementStart.HasBeenCompiled())
{
if (!Helpers.TryPrepareMethod(replacement, replacementHandle))
{
throw new ArgumentException(JIT_ERROR, nameof(replacement));
}
replacementStart = replacementHandle.GetMethodStart();
}
// Copy local value to field
originalMethodStart = originalStart;
// In some cases, the memory might need to be readable / writable:
// Make the memory region rw right away just in case.
Helpers.AllowRW(originalStart);
// Save bytes to change to redirect method
byte[] replBytes = replacementBytes = Helpers.GetJmpBytes(replacementStart);
byte[] origBytes = originalBytes = new byte[replBytes.Length];
Marshal.Copy(originalStart, origBytes, 0, origBytes.Length);
if (start)
{
CopyToStart(replBytes, originalStart);
isRedirecting = true;
}
// Save methods in static array to make sure they're not garbage collected
PersistingMethods.Add(original);
PersistingMethods.Add(replacement);
}