Use Cecil to insert begin/end block around functions - cil

Question

this simple code works fine and allows to add a BeginSample/EndSample call around each Update/LateUpdate/FixedUpdate function. However it doesn't take in consideration early return instructions, for example as result of a condition. Do you know how to write a similar function that take in considerations early returns so that the EndSample call will be executed under every circumstance?
Note that I am not a Cecil expert, I am just learning now. It appears to me that Cecil automatically updates the operations that returns early after calling InsertBefore and similar functions. So if a BR opcode was previously jumping to a specific instruction address, the address will be updated after the insertions in order to jump to the original instruction. This is OK in most of the cases, but in my case it means that an if statement would skip the last inserted operation as the BR operation would still point directly to the final Ret instruction. Note that Update, LateUpdate and FixedUpdate are all void functions.
foreach (var method in type.Methods)
{
if ((method.Name == "Update" || method.Name == "LateUpdate" || method.Name == "FixedUpdate") &&
method.HasParameters == false)
{
var beginMethod =
module.ImportReference(typeof (Profiler).GetMethod("BeginSample",
new[] {typeof (string)}));
var endMethod =
module.ImportReference(typeof (Profiler).GetMethod("EndSample",
BindingFlags.Static |
BindingFlags.Public));
Debug.Log(method.Name + " method found in class: " + type.Name);
var ilProcessor = method.Body.GetILProcessor();
var first = method.Body.Instructions[0];
ilProcessor.InsertBefore(first,
Instruction.Create(OpCodes.Ldstr,
type.FullName + "." + method.Name));
ilProcessor.InsertBefore(first, Instruction.Create(OpCodes.Call, beginMethod));
var lastRet = method.Body.Instructions[method.Body.Instructions.Count - 1];
ilProcessor.InsertBefore(lastRet, Instruction.Create(OpCodes.Call, endMethod));
changed = true;
}
}
as a Bonus, if you can explain to me the difference between Emit and Append a newly created instruction with the same operand. does Append execute an Emit under the hood or does something more?

Answer 1

I may have found the solution, at least apparently it works. I followed the code used to solve a similar problem from here:
https://groups.google.com/forum/#!msg/mono-cecil/nE6JBjvEFCQ/MqV6tgDCB4AJ
I adapted it for my purposes and it seemed to work, although I may find out other issues. This is the complete code:
static bool ProcessAssembly(AssemblyDefinition assembly)
{
var changed = false;
var moduleG = assembly.MainModule;
var attributeConstructor =
moduleG.ImportReference(
typeof(RamjetProfilerPostProcessedAssemblyAttribute).GetConstructor(Type.EmptyTypes));
var attribute = new CustomAttribute(attributeConstructor);
var ramjet = moduleG.ImportReference(typeof(RamjetProfilerPostProcessedAssemblyAttribute));
if (assembly.HasCustomAttributes)
{
var attributes = assembly.CustomAttributes;
foreach (var attr in attributes)
{
if (attr.AttributeType.FullName == ramjet.FullName)
{
Debug.LogWarning("<color=yellow>Skipping already-patched assembly:</color> " + assembly.Name);
return false;
}
}
}
assembly.CustomAttributes.Add(attribute);
foreach (var module in assembly.Modules)
{
foreach (var type in module.Types)
{
// Skip any classes related to the RamjetProfiler
if (type.Name.Contains("AssemblyPostProcessor") || type.Name.Contains("RamjetProfiler"))
{
// Todo: use actual type equals, not string matching
Debug.Log("Skipping self class : " + type.Name);
continue;
}
if (type.BaseType != null && type.BaseType.FullName.Contains("UnityEngine.MonoBehaviour"))
{
foreach (var method in type.Methods)
{
if ((method.Name == "Update" || method.Name == "LateUpdate" || method.Name == "FixedUpdate") &&
method.HasParameters == false)
{
var beginMethod =
module.ImportReference(typeof(Profiler).GetMethod("BeginSample",
new[] { typeof(string) }));
var endMethod =
module.ImportReference(typeof(Profiler).GetMethod("EndSample",
BindingFlags.Static |
BindingFlags.Public));
Debug.Log(method.Name + " method found in class: " + type.Name);
var ilProcessor = method.Body.GetILProcessor();
var first = method.Body.Instructions[0];
ilProcessor.InsertBefore(first,
Instruction.Create(OpCodes.Ldstr,
type.FullName + "." + method.Name));
ilProcessor.InsertBefore(first, Instruction.Create(OpCodes.Call, beginMethod));
var lastcall = Instruction.Create(OpCodes.Call, endMethod);
FixReturns(method, lastcall);
changed = true;
}
}
}
}
}
return changed;
}
static void FixReturns(MethodDefinition med, Instruction lastcall)
{
MethodBody body = med.Body;
var instructions = body.Instructions;
Instruction formallyLastInstruction = instructions[instructions.Count - 1];
Instruction lastLeaveInstruction = null;
var lastRet = Instruction.Create(OpCodes.Ret);
instructions.Add(lastcall);
instructions.Add(lastRet);
for (var index = 0; index < instructions.Count - 1; index++)
{
var instruction = instructions[index];
if (instruction.OpCode == OpCodes.Ret)
{
Instruction leaveInstruction = Instruction.Create(OpCodes.Leave, lastcall);
if (instruction == formallyLastInstruction)
{
lastLeaveInstruction = leaveInstruction;
}
instructions[index] = leaveInstruction;
}
}
FixBranchTargets(lastLeaveInstruction, formallyLastInstruction, body);
}
private static void FixBranchTargets(
Instruction lastLeaveInstruction,
Instruction formallyLastRetInstruction,
MethodBody body)
{
for (var index = 0; index < body.Instructions.Count - 2; index++)
{
var instruction = body.Instructions[index];
if (instruction.Operand != null && instruction.Operand == formallyLastRetInstruction)
{
instruction.Operand = lastLeaveInstruction;
}
}
}
basically what it does is to add a Ret instuction, but then replace all the previous Ret (usually one, why should it be more than one?) with a Leave function (don't even know what it means :) ), so that all the previous jumps remain valid. Differently than the original code, I make the Leave instruction point to the EndSample call before the last Ret