advanced debugging with windbg and sos
Post on 20-May-2015
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Sasha Goldshtein
CTOSela Group
@goldshtnblog.sashag.net
Advanced Debugging with
WinDbg and SOS
www.devconnections.com
ADVANCED DEBUGGING WITH WINDBG AND SOS
AN HOUR FROM NOW,YOU’LL KNOW HOW TO:
Capture crash and hang dumps Pinpoint basic crash causes from
dumps Inspect heap objects and graphs to find
memory leaks Identify deadlocked threads
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ADVANCED DEBUGGING WITH WINDBG AND SOS
DUMPS 101
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ADVANCED DEBUGGING WITH WINDBG AND SOS
A DUMP IS A SNAPSHOT OF A RUNNING PROCESS. YOU CAN
SAVE IT, MOVE IT AROUND, AND ANALYZE IT LATER. YOU CAN’T
“DEBUG” IT.
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ADVANCED DEBUGGING WITH WINDBG AND SOS
TWO TYPES OF DUMPS:
Crash Dump The program crashed
Hang Dump The program didn’t crash
Yet
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ADVANCED DEBUGGING WITH WINDBG AND SOS
SYSINTERNALS PROCDUMP: TAKE DUMPS EASILY, ANYWHERE, AND
WITH NO PUN INTENDED.
Procdump -ma -e MyApp.exeProcdump -h -x C:\temp\myapp.exeProcdump -c 90 -n 3 -s 5 MyApp.exeProcdump -e 1 1234
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ADVANCED DEBUGGING WITH WINDBG AND SOS
CRASH ROOT CAUSE FROM A DUMP
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ADVANCED DEBUGGING WITH WINDBG AND SOS
DRAG AND DROP A DUMP FILE INTO VISUAL STUDIO. CLICK THE
GREEN BUTTON. VOILA, IT WORKS.*
* NITPICKER’S CORNER: YOU NEED SYMBOLS AND SOURCES TO BE LINED UP PROPERLY.
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ADVANCED DEBUGGING WITH WINDBG AND SOS
“
”
YOU WILL INSTALL VISUAL STUDIO ON MY BOXEN OVER MY DEAD BODY. GOOD DAY.
I SAID “GOOD DAY”.
Joe the IT Admin
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ADVANCED DEBUGGING WITH WINDBG AND SOS
10
ENTER:
WinDbg Lightweight GUI debugger
Super-scriptable
Super-extensible
Knows nothing about .NET
SOS WinDbg extension for .NET
Ships with .NET Framework
Or on the symbol server*
Knows all about .NET
* As of CLR 4.0, for GDR versions
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ADVANCED DEBUGGING WITH WINDBG AND SOS
TAKE 2:
Drag and drop a dump file into WinDbg. Hmm. Now what?
!analyze -v !PrintException!CLRStack .load sosex!mk !mdt
.for (r $t0=@ebp; poi(@$t0)!=0; r $t0=poi(@$t0)) { !mln poi(@$t0+4) }
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ADVANCED DEBUGGING WITH WINDBG AND SOS
MEMORY LEAKS: THE EASY WAY
Not in this talk. Shell out $500 for a decent memory profiler.
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ADVANCED DEBUGGING WITH WINDBG AND SOS
MEMORY LEAKS: THE HARD WAY
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ADVANCED DEBUGGING WITH WINDBG AND SOS
WHAT WE NEED:
1. A list of all heap objects
2. A diff of heap objects between dumps
3. Why these heap objects won’t go away
!dumpheap -stat !objsize!gcroot !refs
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ADVANCED DEBUGGING WITH WINDBG AND SOS
DEADLOCKS
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ADVANCED DEBUGGING WITH WINDBG AND SOS
WHAT WE NEED:
1. What is thread X waiting for
2. (Suppose it’s sync object Y)
3. Which thread owns sync object Y
!syncblk !mwaits!mlocks !dlk
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ADVANCED DEBUGGING WITH WINDBG AND SOS
ADDITIONAL REFERENCES
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ADVANCED DEBUGGING WITH WINDBG AND SOS
18
THANK YOU!
Sasha Goldshtein@goldshtn
sashag@sela.co.ilblog.sashag.net
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