Thottam R. Sriram

NTSD and SOS basics

I wanted to take a very simple console application and use ntsd with SOS to debug it. The example demonstrated very simple operations as setting a break point, viewing the managed stack, stack variables, object instance etc.

 

We can go deeper into some of the in depth concepts in the next post.

 

Let us take a simple console application as below:

 

using System;

public class sample

{

    string str;

    public void MyMethod(string arg)

    {

        str = "Member Variable";

        Console.WriteLine("Argument: {0} - {1]", arg, str);

    }

    static void Main()

    {

        sample s = new sample();

        s.MyMethod("Hello");

    }

}

 

We would like to do the following as part of our debugging.

1. Set a break point on MyMethod
2. Watch the variables passed to the method
3. Watch the instance of sample and its variables

 

Let us compile the application with debug enabled. Type

 

csc /Debug App.cs

 

This would generate App.exe and App.pdb. Now, let us start debugging this application:

 

C:\Blog>ntsd App.exe

 

0:000> .symfix

0:000> .sympath+ .

0:000> .reload

0:000> sxe –c  “ “ clrn

0:000> g

0:000> .loadby sos mscorwks

0:000> !bpmd App.exe sample.MyMethod

0:000> g

0:000> !clrstack –a

OS Thread Id: 0x154c (0)

ESP       EIP

001bf268 009700f0 sample.MyMethod(System.String)

    PARAMETERS:

        this = 0x01501964

        arg = 0x01501948

 

001bf26c 009700a9 sample.Main()

    LOCALS:

        <CLR reg> = 0x01501964

 

001bf490 79e8273b [GCFrame: 001bf490]

0:000> !DumpObj 0x01501948

Name: System.String

MethodTable: 790fc6cc

EEClass: 790fc62c

Size: 28(0x1c) bytes

 (C:\Windows\assembly\GAC_32\mscorlib\2.0.0.0__b77a5c561934e089\mscorlib.dll)

String: Hello

Fields:

      MT    Field   Offset                 Type VT     Attr    Value Name

790ff7f0  4000096        4         System.Int32  0 instance        6 m_arrayLength

790ff7f0  4000097        8         System.Int32  0 instance        5 m_stringLength

790fe2dc  4000098        c          System.Char  0 instance       48 m_firstChar

790fc6cc  4000099       10        System.String  0   shared   static Empty    >> Domain:Value  003507e8:790d7eb4 <<

7913cb00  400009a       14        System.Char[]  0   shared   static WhitespaceChars  >> Domain:Value 003507e8:01501548 <<

 

0:000> !DumpObj 0x01501964

Name: sample

MethodTable: 002a301c

EEClass: 002a1200

Size: 12(0xc) bytes

 (C:\blog\app.exe)

Fields:

      MT    Field   Offset                 Type VT     Attr    Value Name

790fc6cc  4000001        4        System.String  0 instance 00000000 str

// Type in a couple of “p” until you get to the place where the local variable is assgned the value “Member Variable”

0:000> !DumpObj 0x01501964

Name: sample

MethodTable: 000c301c

EEClass: 000c1200

Size: 12(0xc) bytes

 (C:\blog\app.exe)

Fields:

      MT    Field   Offset                 Type VT     Attr    Value Name

790fc6cc  4000001        4        System.String  0 instance 01411970 str

 

0:000>  !DumpObj 01411970

Name: System.String

MethodTable: 790fc6cc

EEClass: 790fc62c

Size: 48(0x30) bytes

 (C:\Windows\assembly\GAC_32\mscorlib\2.0.0.0__b77a5c561934e089\mscorlib.dll)

String: Member Variable

Fields:

      MT    Field   Offset                 Type VT     Attr    Value Name

790ff7f0  4000096        4         System.Int32  0 instance       16 m_arrayLength

790ff7f0  4000097        8         System.Int32  0 instance       15 m_stringLength

790fe2dc  4000098        c          System.Char  0 instance       4d m_firstChar

790fc6cc  4000099       10        System.String  0   shared   static Empty    >> Domain:Value  001007c8:790d7eb4 <<

7913cb00  400009a       14        System.Char[]  0   shared   static WhitespaceChars    >> Domain:Value  001007c8:01411548 <<