debugging production sharepoint applications

Debugging Production SharePoint

ApplicationsWouter 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 codeOS

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

• 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

Compile Link 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 CompilationConsole.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

Console metadata

static void WriteLine(string)

JIT Compiler Address

static void WriteLine()

JIT Compiler Address

Native CPU Instructions

Native Address

Executing code with JIT CompilationConsole.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

C# Compiler – Variable Generation

Debug Release

C# Compiler – Inserting NOP

C# Compiler – Inserting NOP

Debug Release

C# Compiler – Branching

C# Compiler – Branching

Debug Release

COMPILE TIME OPTIMIZATIONSDemo

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 startupCompiler switch C# IL Code Quality JIT Native Code Quality

/optimize- /debug- Unoptimized Optimized

/optimize- /debug+ Unoptimized Unoptimized

/optimize+ /debug+ Optimized 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 eliminationUser user = GetUser(3);PrintUser(user);

PrintUser(GetUser(3));

Before

After

JIT – Range check eliminationstatic 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 Inliningpublic 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 Optimizationstatic 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 loadingC:\> 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=1AllowOptimize=0

[assembly: Debuggable(DebuggableAttribute.DebuggingModes.DisableOptimizations | DebuggableAttribute.DebuggingModes.EnableEditAndContinue | DebuggableAttribute.DebuggingModes.IgnoreSymbolStoreSequencePoints | DebuggableAttribute.DebuggingModes.Default)]

DEBUGGING OPTIMIZED CODEDemo

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.dll MyAssembly.pdb

GUID GUIDEqual

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 SHAREPOINTDemo