(We will provide the demo application (simulatebox) available for download to do this demo)!do (!dumpobj) command demo steps
Output: This command prints the state of an object which is
supplied as parameter
Usage: !do {object
address}
When to use ( A sample demo scenario)
Consider A .NET
application processes many patient input records. Users started identifying
that the application crashes occasionally while processing records. A debugger collected the crash dump, he wanted
to examine the process state during the application crash. He wanted to check any invalid data caused
the application crash.
He found that two patient records were under processing
during the time of crash. He wanted to inspect both these records
He printed the object state of these records using dump object
(!do) command.
Let’s do this demo. Here is the demo steps.
(Instead of a dump analysis we shall do a live debugging by
attaching the process. But the troubleshooting approach is similar in both
cases)
We also have a demo video demonstrating the steps
We also have a demo video demonstrating the steps
1.
Open Simulatebox application on (Win 7/8/10) machines
2.
Select !dumpObject demo
3.
Apply button [create patients] . Observe message
“two patient objects created”
4.
We need to inspect these two objects in a
debugger. Open WinDBG (x86 version)
5.
Attach the simulatebox app with debugger
Open File -> Attach to a process menu in debugger
6.
Search and select Simulatebox application in the
dialog box, Apply [ok]
7.
The application
is attached with debugger. Load SOS dll to debugger
(SOS dll contains .NET debugging commands.
So this is an important step to do while
debugging a .NET application using WinDBG)
8.
Apply
command .loadby sos clr
9.
Now we need to search the patient records
existing in the Application’s memory (heap). So to get all patient objects from
heap , Use this command
10.
Apply the
command !dumpheap -type Patient ( see result snapshot below)
11.
We can see two patient objects. Debugger want to
check the state ( values of its data members) of these patient records. He suspects these objects
may be corrupted that led to application crash.
12.
Copy the first object. Dump the object .Apply
!do {object address}
13.
The object state printed. Observe its data
member values
Patiant ID = 1
There is History data member of type String. We need to print its
values. Since string is also a .NET object we can use !do command on its
address. Copy its address available in the Value column.
14.
Apply !do {string address} and observe the
result
15.
Debugger
is able to see the string content “ Patiant A Case history” . Debugger
reasonably believes that it is a good record. he wanted to check the other patient
record.
16.
Copy the second patient object address { result from step 10) and
repeat the steps (11 –
17.
Observe the second object data member (history )
content. There are junk values. The record is corrupted. (figure below)
So by this example, we wanted to show the usability of !do
command. Pretty useful command to check
the internal state of .NET objects .
