Who’s afraid of WinDbg

Dror Helper

[email protected] | http://blog.drorhelper.com | @dhelper

Who’s afraid of WinDBG?

About.Me

• Senior consultant @CodeValue

• Developing software (professionally) since 2002

• Clean coder

• Test Driven Developer

• Blogger: http://blog.drorhelper.com

How I Learned to Stop Worrying and Love WinDbg

From Wikipedia Commons

When we think about debugging

Unfortunately

If (Production && Visual studio)

{

SysAdmin = VeryAngry;

Customer != Permission;

Application = NotWorking;

Debug != DateTime.Now;

}

WinDbg to the rescue

Post mortem analysis of crash/hang dumps

Inspect heap and find memory leaks

Discover deadlocks

Learn more about your application

Basic commands

| list all processes

|. current process

|<x>s switch to process

~ list all threads

~. current thread

~<n>s – switch to thread

k call stack (unmanged)~* all threads~* k – call stack for all threads

Wait, you’re forgot something

For proper debugging you’ll need symbols

1. lm show all modules + symbol information

2. .symfix + .reload –f

3. ld Loads symbols for the specified module

Or use

File Symbol file path

ICanHasWindows!

PART I – CRASH ANALYSIS

11

Analyzing Crush dump

A minidump is a snapshot of an application state:{

Process(s)Thread(s)Module(s)Register(s)Memory infoHandlesCall stack…

}

Creating MiniDumps

WinDbg

Task Manager/ProcEx

ADPlus (Debugging tools for windows)

ProcDump (sysinternals)

sos.dll

WinDBG extension

Knows .NET

Ships with .NET framework/symbol server

.loadby sos mscorwks (.net 3.5 or earlier)

.loadby sos clr (.net 4.0 or later)

Now what?

1. Load MiniDump in WinDBG

2. Symbols!

3. Load sos.dll

4. !analyze –v

More crash analysis commands (sos)

!printexception

!threads

!dae (dump all exceptions)

!dso (dump stack objects)

!clrstack

-p (shows parameters and values)

-l (show locals)

-a (same as –p –l)

PART II - INVESTIGATING MEMORY ISSUES

17

Finding memory issues

1. Look at heap

2. List all objects

3. Dive in to see specific object

4. Compare with previous results

!dumpheap -stat

!dumpheap –type

!do

!gcroot

Other memory related commands

!FinalizeQueue!objsize!GCHandleLeaks

!dumpgen!gcgen!refs!mk!mdt

PART III – DEADLOCK DETECTION

20

R1

R2

P2P1

Deadlock detection

1. .load <folder>\sosex.dll

2. !dlk

Other options:!syncblk/!DumpHeap –thinlockPlain old !clrstack!mlocks!mwaits

Making WinDBG user friendly(ier)

.cmdtree <cmd file>

.prefer_dml 1

Dror Helper

C: 972.05.7668543

e: [email protected]

B: blog.drorhelper.com