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 <<


 


Comments (6)

  1. Dan McKinley says:

    Unfortunately, much of this does not currently work for the public. For example, the version of SOS that ships with the 2.0 CLR is old and does not include the !bpmd command. (There are, of course, more manual ways to set a managed breakpoint.)

    There is no 2.0 version of SOS currently included in the debugging tools distribution.

  2. Bridgette Landers [CLR] says:

    Dan,

    I loaded the 2.0.50727.42 version of SOS.dll and confirmed that it includes !bpmd.  That’s the version of SOS that ships with the 2.0 redist. I think that version of SOS also ships with the 2.0  SDK.  If you find a package that includes the wrong SOS, please tell us exactly where it came from so we can investigate.

    Some early 2.0 beta builds might have included a version of SOS that didn’t have !bpmd.  And  WinDbg ships with an old build of SOS that only works with 1.1 and 1.0.  But if you’re debugging 2.0 then your SOS should have version # 2.0.50727.42.

    HTH,

    Bridgette

  3. Dan McKinley says:

    I just checked and !bpmd is there. HOWEVER, it’s not listed in the output of !help, so I always assumed it wasn’t. Thanks.

  4. Thottam Sriram [CLR] says:

    I tried !help and see BPMD there as well.

  5. Mahesh A says:

    Nice and simple. 2 minute kick-start to managed debugging and gives pointers in the right direction.

    Looking forward to future aricles on debugging of multi-threaded applications.

  6. Andrew Bradnan says:

    Where is the good old EAX register (the clr equivalent) after a .call?  I’m sure I’m looking right at it, but it doesn’t appear to be on the stack.  Thanks