Debugging Production SharePoint Applications Wouter van Vugt

Agenda How.NET and the CLR work Optimizing code and the effect on debuggers Debugging third party code

HOW.NET AND THE CLR WORK

.NET Applications Written in any language Executed in a runtime called CLR – Shield code from hardware specifics Java: One language, multi OS.NET: Many languages, one OS (and Mono) – Allows various types of preprocessing of code OS CLR App

Common Language Runtime Operation Memory management Thread synchronization Error handling Type Safety Security Code Access Security Data Execution Prevention (OS) Address Space Layout Randomization (OS) Execution Intermediate Language

Type Safety – A pointer of a specific type can never point to an object which is not of that type! – Checked at compile AND runtime! – Knowing the actual type enables Reading its data  Quite useful in debugging Calling its functions Car c = new Person() ‘Pointer type’ Pointer Object type

TRY AND CIRCUMVENT TYPE SAFETY Demo

Creating.NET Applications C#, C++, VB.NET, F#.... (40+) Module PDB CompileLink Assembly PDB

Executing code Assemblies contain mostly IL code – IL is the ‘Machine code’ for.NET – Compiled to native instructions at runtime through the JIT Compiler – Enough information remains to decompile back to source! C# Machine Code Language richness compared IL

Executing code with JIT Compilation Console.WriteLine("Hi"); Console.WriteLine("There"); JIT Compiler -Lookup IL for method -Compile IL to native -Modify metadata to point to compiled code -Jump to compiled code JIT Compiler -Lookup IL for method -Compile IL to native -Modify metadata to point to compiled code -Jump to compiled code Console metadata static void WriteLine(string) JIT Compiler Address static void WriteLine() JIT Compiler Address Native CPU Instructions Native Address

Executing code with JIT Compilation Console.WriteLine("Hi"); Console.WriteLine("There"); Console metadata static void WriteLine(string) JIT Compiler -Lookup IL for method -Compile IL to native -Modify metadata to point to compiled code -Jump to compiled code Native Address static void WriteLine() JIT Compiler Address Native CPU Instructions

Code optimization Compile-time – Constant value folding – Remove Branch to next instruction and NOP instructions used to break on control flow, {, }, EndIf etc – Overflow checking – … During JIT – Eliminate local variables – Range check elimination – Method inlining – Tail call optimization – Common subexpression elimination – Dead code elimination – Loop unrolling – …

Running non optimized code Breakpoints Edit and continue

C# Compiler – Variable Generation

DebugRelease

C# Compiler – Inserting NOP

DebugRelease

C# Compiler – Branching

DebugRelease

COMPILE TIME OPTIMIZATIONS Demo

Just In Time Compilation Transformation of MSIL to native x86 / x64 / ARM etc Can optimize code – Mathematically ensured correctness Takes a small performance hit during startup Compiler switchC# IL Code QualityJIT Native Code Quality /optimize- /debug-UnoptimizedOptimized /optimize- /debug+Unoptimized /optimize+ /debug+Optimized

NGEN.exe JIT Compilation incurs a runtime cost NGEN pre-compiles MSIL assemblies to machine code Runs as a service in the background Also used by the “.NET Runtime Optimization Service”

JIT - Local variable elimination User user = GetUser(3); PrintUser(user); PrintUser(GetUser(3)); Before After

JIT – Range check elimination static int[] _array = new int[10]; static volatile int _i; static void Main(string[] args) { for (int i = 0; i < _array.Length; ++i) _i += _array[i]; } static int[] _array = new int[10]; static volatile int _i; static void Main(string[] args) { int[] localRef = _array; for (int i = 0; i < localRef.Length; ++i) _i += localRef[i]; } Before After

JIT – Method Inlining public class Program { public static int And(int first, int second) { return first & second; } static void Main(string[] args) { int i = And(5, 4); } public class Program { static void Main(string[] args) { int i = 5 & 4; } Before After

JIT – Tail Call Optimization static void Main(string[] args) { TestTailCallOptimization(); } public static void TestTailCallOptimization() { string s = "Test"; TailCall1(s); } static void TailCall1(string s) { Console.WriteLine(s); TailCall2(s); } static void TailCall2(string s) { Console.WriteLine(s + s); }

Loading non-precompiled assemblies Native NGEN images are hard to debug – Remove the NGEN image – Or, prevent NGEN image from loading C:\> SET COMPLUS_ZAPDISABLE=1 C:\> NGEN uninstall MyAssembly

Preventing JIT optimization Creating debug builds – JIT prevented through compile time attributes INI file MyAssembly.ini In Visual Studio, on module load after attach [.NET Framework Debugging Control] GenerateTrackingInfo=1 AllowOptimize=0 [assembly: Debuggable(DebuggableAttribute.DebuggingModes.DisableOptimizations | DebuggableAttribute.DebuggingModes.EnableEditAndContinue | DebuggableAttribute.DebuggingModes.IgnoreSymbolStoreSequencePoints | DebuggableAttribute.DebuggingModes.Default)] [assembly: Debuggable(DebuggableAttribute.DebuggingModes.DisableOptimizations | DebuggableAttribute.DebuggingModes.EnableEditAndContinue | DebuggableAttribute.DebuggingModes.IgnoreSymbolStoreSequencePoints | DebuggableAttribute.DebuggingModes.Default)]

DEBUGGING OPTIMIZED CODE Demo

Debugging code PDB files are as essential as code! Breakpoints can do way more than break Tracing is cheaper than debugging IntelliTrace can run in production

PDB Files Contain vital debugging information No PDB? Severely limited debugging experience! Minimal investment: Symbol server Managed PDB files contain – Source file names / line numbers – Local variable names – Alternate streams  Used by TFS

Symbol Servers Central repository for storing debug symbols File system based technology Integrated into Team Foundation and Visual Studio

Locating debug symbols PDB files are located – Same directory as module – Hardcoded path in module – Symbol server cache – Symbol server MyAssembly.dllMyAssembly.pdb GUID Equal

Dumpbin.exe Use to peek inside PE files

Prevent loading all PDBs

Visual Studio Source Server support Allows Visual Studio to download relevant source files automatically from a repository.

Configuring Symbol Locations

PDB alternate streams Used by TFS to store server path to sources

SYMBOL SERVERS, SOURCE SERVERS AND SOURCE INDEXING Demo

Working with break points

Setting breakpoints on automatic properties Use ‘Break at function’ and enter get_name

Setting breakpoints on automatic properties Inspect callstack / locals window

Debugging third party code Red Gate.NET Reflector PRO – Decompile assemblies into source code – Generate PDB file from assembly + source – Enables debugging third party code

Enabling remote debugging Run Remote Debugging x86 or x64 Give permissions Connect

DEBUGGING SHAREPOINT Demo