private static void WritePrefixes(ILEmitter il, MethodBase original, ILEmitter.Label returnLabel,
Dictionary <string, VariableDefinition> variables, List <MethodInfo> prefixes)
{
// Prefix layout:
// Make return value (if needed) into a variable
// Call prefixes
// If method returns a value, add additional logic to allow skipping original method
if (prefixes.Count == 0)
{
return;
}
Logger.Log(Logger.LogChannel.Info, () => "Writing prefixes");
// Start emitting at the start
il.emitBefore = il.IL.Body.Instructions[0];
if (!variables.TryGetValue(RESULT_VAR, out var returnValueVar))
{
var retVal = AccessTools.GetReturnedType(original);
returnValueVar = variables[RESULT_VAR] = retVal == typeof(void) ? null : il.DeclareVariable(retVal);
}
// Flag to check if the orignal method should be run (or was run)
// Only present if method has a return value and there are prefixes that modify control flow
var runOriginal = prefixes.Any(p => p.ReturnType == typeof(bool))
? il.DeclareVariable(typeof(bool))
: null;
// Init runOriginal to true
if (runOriginal != null)
{
il.Emit(OpCodes.Ldc_I4_1);
il.Emit(OpCodes.Stloc, runOriginal);
}
// If runOriginal flag exists, we need to add more logic to the method end
var postProcessTarget = returnValueVar != null?il.DeclareLabel() : returnLabel;
foreach (var prefix in prefixes)
{
EmitCallParameter(il, original, prefix, variables, false);
il.Emit(OpCodes.Call, prefix);
if (!AccessTools.IsVoid(prefix.ReturnType))
{
if (prefix.ReturnType != typeof(bool))
{
throw new InvalidHarmonyPatchArgumentException(
$"Prefix patch {prefix.GetID()} has return type {prefix.ReturnType}, but only `bool` or `void` are permitted", original, prefix);
}
if (runOriginal != null)
{
// AND the current runOriginal to return value of the method (if any)
il.Emit(OpCodes.Ldloc, runOriginal);
il.Emit(OpCodes.And);
il.Emit(OpCodes.Stloc, runOriginal);
}
}
}
if (runOriginal == null)
{
return;
}
// If runOriginal is false, branch automatically to the end
il.Emit(OpCodes.Ldloc, runOriginal);
il.Emit(OpCodes.Brfalse, postProcessTarget);
if (returnValueVar == null)
{
return;
}
// Finally, load return value onto stack at the end
il.emitBefore = il.IL.Body.Instructions[il.IL.Body.Instructions.Count - 1];
il.MarkLabel(postProcessTarget);
il.Emit(OpCodes.Ldloc, returnValueVar);
}
private static void WriteFinalizers(ILEmitter il, MethodBase original, ILEmitter.Label returnLabel,
Dictionary <string, VariableDefinition> variables,
List <MethodInfo> finalizers)
{
// Finalizer layout:
// Create __exception variable to store exception info and a skip flag
// Wrap the whole method into a try/catch
// Call finalizers at the end of method (simulate `finally`)
// If __exception got set, throw it
// Begin catch block
// Store exception into __exception
// If skip flag is set, skip finalizers
// Call finalizers
// If __exception is still set, rethrow (if new exception set, otherwise throw the new exception)
// End catch block
if (finalizers.Count == 0)
{
return;
}
Logger.Log(Logger.LogChannel.Info, () => "Writing finalizers");
il.emitBefore = il.IL.Body.Instructions[il.IL.Body.Instructions.Count - 1];
// Mark the original method return label here if it hasn't been yet
il.MarkLabel(returnLabel);
if (!variables.TryGetValue(RESULT_VAR, out var returnValueVar))
{
var retVal = AccessTools.GetReturnedType(original);
returnValueVar = variables[RESULT_VAR] = retVal == typeof(void) ? null : il.DeclareVariable(retVal);
}
// Create variables to hold custom exception
var skipFinalizersVar = il.DeclareVariable(typeof(bool));
variables[EXCEPTION_VAR] = il.DeclareVariable(typeof(Exception));
// Start main exception block
var mainBlock = il.BeginExceptionBlock(il.DeclareLabelFor(il.IL.Body.Instructions[0]));
bool WriteFinalizerCalls(bool suppressExceptions)
{
var canRethrow = true;
foreach (var finalizer in finalizers)
{
var start = il.DeclareLabel();
il.MarkLabel(start);
EmitCallParameter(il, original, finalizer, variables, false);
il.Emit(OpCodes.Call, finalizer);
if (finalizer.ReturnType != typeof(void))
{
il.Emit(OpCodes.Stloc, variables[EXCEPTION_VAR]);
canRethrow = false;
}
if (suppressExceptions)
{
var exBlock = il.BeginExceptionBlock(start);
il.BeginHandler(exBlock, ExceptionHandlerType.Catch, typeof(object));
il.Emit(OpCodes.Pop);
il.EndExceptionBlock(exBlock);
}
}
return(canRethrow);
}
// First, store potential result into a variable and empty the stack
if (returnValueVar != null)
{
il.Emit(OpCodes.Stloc, returnValueVar);
}
// Write finalizers inside the `try`
WriteFinalizerCalls(false);
// Mark finalizers as skipped so they won't rerun
il.Emit(OpCodes.Ldc_I4_1);
il.Emit(OpCodes.Stloc, skipFinalizersVar);
// If __exception is not null, throw
var skipLabel = il.DeclareLabel();
il.Emit(OpCodes.Ldloc, variables[EXCEPTION_VAR]);
il.Emit(OpCodes.Brfalse, skipLabel);
il.Emit(OpCodes.Ldloc, variables[EXCEPTION_VAR]);
il.Emit(OpCodes.Throw);
il.MarkLabel(skipLabel);
// Begin a generic `catch(Exception o)` here and capture exception into __exception
il.BeginHandler(mainBlock, ExceptionHandlerType.Catch, typeof(Exception));
il.Emit(OpCodes.Stloc, variables[EXCEPTION_VAR]);
// Call finalizers or skip them if needed
il.Emit(OpCodes.Ldloc, skipFinalizersVar);
var postFinalizersLabel = il.DeclareLabel();
il.Emit(OpCodes.Brtrue, postFinalizersLabel);
var rethrowPossible = WriteFinalizerCalls(true);
il.MarkLabel(postFinalizersLabel);
// Possibly rethrow if __exception is still not null (i.e. suppressed)
skipLabel = il.DeclareLabel();
il.Emit(OpCodes.Ldloc, variables[EXCEPTION_VAR]);
il.Emit(OpCodes.Brfalse, skipLabel);
if (rethrowPossible)
{
il.Emit(OpCodes.Rethrow);
}
else
{
il.Emit(OpCodes.Ldloc, variables[EXCEPTION_VAR]);
il.Emit(OpCodes.Throw);
}
il.MarkLabel(skipLabel);
il.EndExceptionBlock(mainBlock);
if (returnValueVar != null)
{
il.Emit(OpCodes.Ldloc, returnValueVar);
}
}
private static void WritePostfixes(ILEmitter il, MethodBase original, ILEmitter.Label returnLabel,
Dictionary <string, VariableDefinition> variables, List <MethodInfo> postfixes)
{
// Postfix layout:
// Make return value (if needed) into a variable
// If method has return value, store the current stack value into it (since the value on the stack is the return value)
// Call postfixes that modify return values by __return
// Call postfixes that modify return values by chaining
if (postfixes.Count == 0)
{
return;
}
Logger.Log(Logger.LogChannel.Info, () => "Writing postfixes");
// Get the last instruction (expected to be `ret`)
il.emitBefore = il.IL.Body.Instructions[il.IL.Body.Instructions.Count - 1];
// Mark the original method return label here
il.MarkLabel(returnLabel);
if (!variables.TryGetValue(RESULT_VAR, out var returnValueVar))
{
var retVal = AccessTools.GetReturnedType(original);
returnValueVar = variables[RESULT_VAR] = retVal == typeof(void) ? null : il.DeclareVariable(retVal);
}
if (returnValueVar != null)
{
il.Emit(OpCodes.Stloc, returnValueVar);
}
foreach (var postfix in postfixes.Where(p => p.ReturnType == typeof(void)))
{
EmitCallParameter(il, original, postfix, variables, true);
il.Emit(OpCodes.Call, postfix);
}
// Load the result for the final time, the chained postfixes will handle the rest
if (returnValueVar != null)
{
il.Emit(OpCodes.Ldloc, returnValueVar);
}
// If postfix returns a value, it must be chainable
// The first param is always the return of the previous
foreach (var postfix in postfixes.Where(p => p.ReturnType != typeof(void)))
{
EmitCallParameter(il, original, postfix, variables, true);
il.Emit(OpCodes.Call, postfix);
var firstParam = postfix.GetParameters().FirstOrDefault();
if (firstParam == null || postfix.ReturnType != firstParam.ParameterType)
{
if (firstParam != null)
{
throw new InvalidHarmonyPatchArgumentException(
$"Return type of pass through postfix {postfix.GetID()} does not match type of its first parameter", original, postfix);
}
throw new InvalidHarmonyPatchArgumentException($"Postfix patch {postfix.GetID()} must have `void` as return type", original, postfix);
}
}
}
