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Debugging Tools for Windows: The psscor2 Managed Code Debugger Extension

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SOS has long been the standard when dealing with managed code using the native debuggers but there are additional extensions that add even more value to the debugging process. Unfortunately, these added and powerful extensions were only available to Microsoft engineers making the debugging process more tedious for third party developers. Fortunately, Microsoft very recently decided to release a very commonly used debugger extension to the public called psscor2. Mario Hewardt takes a look at some of the powerful commands that are available as part of the psscor2 debugger extension.
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Introduction

Debugging Tools for Windows is an incredibly useful toolbox that every developer should know how to use. It contains powerful debuggers, troubleshooting tools, and debugger extensions that make debugging different technologies on Windows much easier. Amongst the debugger extensions is an extension called SOS, which allows developers to peek into the CLR itself to make debugging of managed code applications much more efficient. SOS has long been the standard when dealing with managed code using the native debuggers, but there are additional extensions that add even more value to the debugging process. Unfortunately, these added and powerful extensions were only available to Microsoft engineers, making the debugging process more tedious for third party developers. Fortunately, Microsoft very recently decided to release a very commonly used debugger extension to the public called psscor2. In this article, I will take a look at some of the powerful commands that are available as part of the psscor2 debugger extension.

Installation

The psscor2 debugger extension can be downloaded from

http://www.microsoft.com/downloads/details.aspx?FamilyID=5c068e9f-ebfe-48a5-8b2f-0ad6ab454ad4&displayLang=en

The installation process is very simple and comes in the form of a ZIP file that contains the psscor2.dll for all three flavors (x86, amd64, ia64). Simply extract the flavor you are interested in and place it in your favorite debugger extensions folder (I typically install it into the default debugger folder). You can then load the debugger extension in any of your debug sessions using the .load debugger command as shown below:

New Commands

Psscor2 provides a slew of new commands in different areas of .NET. Some commands are specific to ASP.NET applications, whereas others are related to the core of the CLR. In this section of the article I will describe some of the new commands that are available as part of this new and exciting debugger extension.

ASP.NET Commands

A task when investigating ASP.NET problems is to figure out which ASPX pages are currently loaded into the IIS hosting process. The ASPXPages command can be used for this purpose. For example, attaching the debugger to an IIS hosting process (w3wp.exe) with a simple ASPX page loaded, the output of the ASPXPages command is shown below:

0:024> !ASPXPages
Going to dump the HttpContexts found in the heap.
Loading the heap objects into our cache.
HttpContext    Timeout  Completed     Running  ThreadId ReturnCode   Verb RequestPath+QueryString
0x00000000ff92c818    0                         no       980 Sec     XXX        200    /test/
0x00000000ff94d258      110 Sec        no       980 Sec     XXX        200   GET /test/default.aspx
Total 2 HttpContext objects

As you can see, the information presented is quite useful to get an overall idea behind the ASPX usage. If you want to see the IP addresses of the client and server, you can specify the –ip switch.

Another very useful task is to be able to see what the thread configuration is for the given ASP.NET application. For example, if the thread configuration is set to 100 and your debug session seems to imply that there are several hundred threads, the configuration may be an issue. To see the thread configuration, the DumpThreadConfig command can be used. An example of the output is shown below:

0:024> !DumpThreadConfig

Loading the heap objects into our cache.
0x0000000000000000 is not a ServicePoint object
autoConfig is true
Number of Processors: 4  (multiplied by number to get total value).
 MaxWorkerThreads: 100 (400)
 MaxIoThreads: 100 (400)
 minFreeThreads: 88 (352)
 minLocalRequestFreeThreads: 76 (304)
 maxConnection: 0 (0)

In the output above, we can see thread configuration such as max number of workers and Io threads as well as other useful information.

It is quite common for ASP.NET applications to utilize the built in ASP.NET application cache. Similarly, it is quite common when debugging to inspect the cache to make sure the source of the problem isn’t related to any issues within the cache itself. Psscor2 offers the DumpASPNETCache command to help with this task. For example, the following shows the output of the command when run against a simple ASP.NET application. For the sake of brevity, I have used the –stat switch since the detailed output for each object is quite verbose:

0:024> !DumpASPNETCache -stat
Going to dump the ASP.NET Cache.
Loading the heap objects into our cache.
Statistics:
        MT    Count    TotalSize       Change Class Name
0x000007fef67f1750        1           48            1 System.Reflection.Assembly
0x000007fee9bceef0        1           48            1 System.Web.Security.FileSecurityDescriptorWrapper
0x000007fee9b73d50        1           88            1 System.Web.Compilation.BuildResultCompiledTemplateType
0x000007fee9bfec38        5          320            5 System.Web.CachedPathData
0x000007fee9bffe38       10          400           10 System.Web.Configuration.MapPathCacheInfo
0x000007fee2f27880        2          928            2 System.Web.Mobile.MobileCapabilities
Total 20 objects, Total size: 1,832

If there is anything strange (i.e., objects you don’t expect) you can use the same command without the –stat switch to get more detailed information.

In addition to the ASP.NET related commands above, there are other new commands as well such as DumpHttpRuntime, DumpHttpContext, DumpRequestTable, DumpHistoryTable and DumpRequestQueues. All of the commands simplify the inspection of ASP.NET state, and I encourage you to play around with the commands to get an idea of the incredible time savings that they can accomplish.

Date and Time Commands

Many applications make use of the data type System.DateTime. When debugging, however, it can sometimes be hard to convert the values of a DateTime object to a more human readable form. For example, the address 0x000000000016eef0 represents a DateTime value type instance. If I dump the contents of that memory I’ll get something similar to what is shown below:

0:000> dd 0x000000000016eef0
00000000`0016eef0  af64f480 88cc9fc5 af64f480 88cc9fc5
00000000`0016ef00  0000001d 00000000 00000001 00000000
00000000`0016ef10  00033988 000007ff f93bd502 000007fe
00000000`0016ef20  0216c960 00000000 f929240a 000007fe
00000000`0016ef30  f9165890 000007fe 00000000 00000000
00000000`0016ef40  0016f1c8 00000000 00000000 00000000
00000000`0016ef50  0016f1a0 00000000 00000000 00000000
00000000`0016ef60  003a87e0 00000000 f9279fd3 000007fe

The output doesn’t really tell me in a nice way what the DateTime instance contains. Enter the new psscor2 commands PrintDateTime and ConvertVTDateToDate. The ConvertVTDatetoDate (shortcut cvtdd) command takes as input the address of a value type and outputs the result to the screen. Using the same pointer as above, the output of the ConvertVTDateToDate command shows:

0:000> !cvtdd 0x000000000016eef0
As a TimeSpan: 11409061.18:38:59.8003808
As a DateTime: 04/01/2010 15:50:54

The PrintDateTime, on the other hand, takes an address to a reference type and outputs the DateTime in a nice format much like the ConvertVTDateToDate command.

General Object Inspection

In today's world, many applications make use of XML in one form or another. In the .NET world, a common way to represent an XML document is to use the XmlDocument class. The XmlDocument class provides a ton of great functionality to manipulate different XML snippets. During debugging, however, it is painstakingly difficult to find out what the XML looks like based solely on a pointer to an XmlDocument instance. For example, if I dump out an instance of the XmlDocument class I see the following (abbreviated):

0:000> !do 0x000000000267c730
Name: System.Xml.XmlDocument
MethodTable: 000007fef5e1b218
EEClass: 000007fef5cdbd00
Size: 304(0x130) bytes
GC Generation: 0
 (C:\Windows\assembly\GAC_MSIL\System.Xml\2.0.0.0__b77a5c561934e089\System.Xml.dll)
Fields:
              MT            Field           Offset                 Type VT             Attr            Value Name
000007fef5e1b5f8  40008d7        8   System.Xml.XmlNode  0 instance 0000000000000000 parentNode
000007fef5e1e5c0  40008e7       10 ...XmlImplementation  0 instance 000000000267c860 implementation
000007fef5e1e7b8  40008e8       18 ....Xml.DomNameTable  0 instance 000000000267cdb0 domNameTable
000007fef5e1e910  40008e9       20 ...Xml.XmlLinkedNode  0 instance 0000000002680078 lastChild
000007fef5e1f340  40008ea       28 ...l.XmlNamedNodeMap  0 instance 0000000000000000 entities
000007fef7dc65e8  40008eb       30 ...ections.Hashtable  0 instance 0000000000000000 htElementIdMap
000007fef7dc65e8  40008ec       38 ...ections.Hashtable  0 instance 0000000000000000 htElementIDAttrDecl
000007fef5e312c8  40008ed       40 ...Schema.SchemaInfo  0 instance 0000000000000000 schemaInfo
000007fef5e251a0  40008ee       48 ...hema.XmlSchemaSet  0 instance 0000000000000000 schemas
000007fef7dbde60  40008ef      120       System.Boolean  1 instance                1 reportValidity
000007fef7dbde60  40008f0      121       System.Boolean  1 instance                0 actualLoadingStatus
000007fef5e32070  40008f1       50 ...angedEventHandler  0 instance 0000000000000000 onNodeInsertingDelegate
000007fef5e32070  40008f2       58 ...angedEventHandler  0 instance 0000000000000000 onNodeInsertedDelegate
000007fef5e32070  40008f3       60 ...angedEventHandler  0 instance 0000000000000000 onNodeRemovingDelegate

That really doesn’t tell me much about the actual XML content. Fortunately, psscor2 introduces the DumpXmlDocument command that takes a pointer to an XmlDocument instance and produces the actual XML content:

0:000> !DumpXmlDocument 0x000000000267c730
<Configuration Product="HomeStudentr">
   <Display Level="none" CompletionNotice="No" SuppressModal="Yes" AcceptEula="no">
   </Display>
   <Setting Id="OEM" Value="1">
   </Setting>

   <Setting Id="REFERRAL" Value="QW2E3T5A">
   </Setting>
   <Setting Id="SETUP_REBOOT" Value="NEVER">
   </Setting>
   <AddLanguage Id="es-es">
   </AddLanguage>

</Configuration>

Another great command is the DumpCollection command, which is able to dump the contents of one of the following:

  • ArrayList
  • HashTable
  • Queue
  • Collections derived from DictionaryBase
  • Collections derived from NamedObjectCollectionBase

For example, if I had an ArrayList that contained five names (of type string), the output of the DumpCollection command would look like:

0:000> !DumpCollection  0x000000000270c738
Going to dump the Collection passed.
Collection 0x000000000270c738: System.Collections.ArrayList
[0] 000000000270c6c8
    Name: System.String
    MethodTable: 000007fef7dbec90
    EEClass: 000007fef79cb038
    Size: 36(0x24) bytes
    GC Generation: 0
     (C:\Windows\assembly\GAC_64\mscorlib\2.0.0.0__b77a5c561934e089\mscorlib.dll)
    String:     Gemma

    Fields:
                  MT            Field           Offset                 Type VT             Attr            Value Name
    000007fef7dc5f00  4000096        8         System.Int32  1 instance                6 m_arrayLength
    000007fef7dc5f00  4000097        c         System.Int32  1 instance                5 m_stringLength
    000007fef7dc06d8  4000098       10          System.Char  1 instance               47 m_firstChar
    000007fef7dbec90  4000099       20        System.String  0   shared           static Empty
                                 >> Domain:Value  00000000001bebf0:00000000026a1308 <<
    000007fef7dc0588  400009a       28        System.Char[]  0   shared           static WhitespaceChars
                                 >> Domain:Value  00000000001bebf0:00000000026a1a50 <<
[1] 000000000270c6f0
    Name: System.String
    MethodTable: 000007fef7dbec90
    EEClass: 000007fef79cb038
    Size: 32(0x20) bytes
    GC Generation: 0
     (C:\Windows\assembly\GAC_64\mscorlib\2.0.0.0__b77a5c561934e089\mscorlib.dll)
    String:     Pia
    Fields:
                  MT            Field           Offset                 Type VT             Attr            Value Name
    000007fef7dc5f00  4000096        8         System.Int32  1 instance                4 m_arrayLength
    000007fef7dc5f00  4000097        c         System.Int32  1 instance                3 m_stringLength
    000007fef7dc06d8  4000098       10          System.Char  1 instance               50 m_firstChar
    000007fef7dbec90  4000099       20        System.String  0   shared           static Empty
                                 >> Domain:Value  00000000001bebf0:00000000026a1308 <<

    000007fef7dc0588  400009a       28        System.Char[]  0   shared           static WhitespaceChars
                                 >> Domain:Value  00000000001bebf0:00000000026a1a50 <<
[2] 000000000270c710
    Name: System.String
    MethodTable: 000007fef7dbec90
    EEClass: 000007fef79cb038
    Size: 36(0x24) bytes
    GC Generation: 0
     (C:\Windows\assembly\GAC_64\mscorlib\2.0.0.0__b77a5c561934e089\mscorlib.dll)
    String:     Mario
    Fields:
                  MT            Field           Offset                 Type VT             Attr            Value Name
    000007fef7dc5f00  4000096        8         System.Int32  1 instance                6 m_arrayLength
    000007fef7dc5f00  4000097        c         System.Int32  1 instance                5 m_stringLength
    000007fef7dc06d8  4000098       10          System.Char  1 instance               4d m_firstChar
    000007fef7dbec90  4000099       20        System.String  0   shared           static Empty
                                 >> Domain:Value  00000000001bebf0:00000000026a1308 <<
    000007fef7dc0588  400009a       28        System.Char[]  0   shared           static WhitespaceChars
                                 >> Domain:Value  00000000001bebf0:00000000026a1a50 <<

The last general object inspection command we will discuss is the PrintIPAddress command. Similarly to the above objects, dumping out the raw form of the System.Net.IPAddress doesn’t easily tell you what the textual representation of the IP address is. The PrintIPAddress comes to rescue. By specifying the address to the IPAddress object, PrintIPAddress will give you the easily digestible version of the IPAdress object:

0:000> !PrintIPAddress 0x00000000024bc6c8

254.7.0.0 

Summary

In this article I took a look at the new managed code debugger extension called psscor2. Psscor2 contains a plethora of powerful commands, both in the general object inspection arena and in the ASP.NET arena, allowing developers to be much more efficient in their debug sessions. While I only looked at some of the more commonly used commands in psscor2, there is more to the debugger extension, and I urge you to take a closer look at some of the other commands it has to offer.

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