who’s afraid of windbg
TRANSCRIPT
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
B: blog.drorhelper.com