Posts Tagged ‘debug’

On Debugging Virtual Applications Part 4: The Case of the Missing Dump

September 27, 2016 Leave a comment

I’ve been blogging lately (well . . . not exactly lately) about debugging virtual applications that misbehave – whether by hanging, crashing, or spewing some strange error message. In discussing the use of tools, one question I often get is the relationship of attaching the debuggers to the virtual application inside or outside the virtual environment. With App-V 5, it only matters in certain circumstances at the user mode level as virtualized applications work from a state-separated registry and file system that leverage the native file system and registry.

When a developer is troubleshooting a virtual application that they have developed, or an IT Pro Debugger is attempting to reverse engineer an application issue, I usually recommend they attach to the virtual process as they would any other application at first. You may decide due to necessity or preference to attach a debugger or a tool to the virtual application process within the context of the virtual environment by launching it in the application’s “bubble.” You may want to be advised that once you do this, the debugging tool will also be running virtually and will behave accordingly.

I bring this up due to an interesting issue that was encountered by one of our partners a while back: There was an issue with a plug-in to Internet Explorer causing it to hang shortly after the BHO had been triggered while running in standard isolation (i.e. no Dynamic Virtualization involved.) Given that the individual had developed the code for the plug-in, they wanted to capture a full user mode memory dump of the instance of Internet Explorer that was running virtually. The issue could not be reproduced in the developer’s environment so there was the usual suspicion of something environmental being a factor. Since standard WER (Windows Error Reporting) is somewhat limited by default, the customer was leveraging ProcDump -h to capture a user mode memory dump of the IEXPLORE.EXE process.

Here’s the thing: while Procdump appeared to attach to and generate a dump successfully, there were no dumps to be found per the developer. Upon further inquiry, I found that the developer was doing the following:

  1. Using C: as a target. This is not good on many levels.
  2. Running ProcDump from a command prompt in the application’s (IEXPLORE.EXE) virtual environment.

While running it in the bubble was not necessarily a bad thing, I had the developer simply redirect the output to %TEMP% instead of C:. The dumps showed up as normal. When asked why C: mattered, I told him that due to coupling factors (specifying an unexcluded folder, VFS Write mode, running as an administrator, and launching in the bubble, the dump file was treated as application state data and was redirected to the VFS CoW location. Upon a quick demonstration, it was discovered buried beneath the user’s VFS folder.





I should note that there shouldn’t be any concern with regards to the usability of these redirected dumps. I will also note that upon repairing the App-V package in questions, the user freed up around 12GB of disk space. I guess they had been trying the ProcDump command quite a bit. J


On Debugging Virtual Applications: Part 3 – Situations where a Debugger is most needed for Virtual Applications

February 23, 2016 1 comment

In parts 1 and 2 of this series, I’ve covered some of the basic fundamentals of the concept of debugging compiled software code which, for the most part, has been a black box for many working with virtual applications. In part 3, I would like to now move the discussion towards those situations that warrant further debugging analysis. Note that for this topic, I will be limiting the scope to specifically user mode applications as application virtualization products like App-V are pretty much limited to these.

Native Code vs. Managed Code

Managed Code refers to computer source code that will only executive under the management of a special runtime module. Technically managed code refers to any code that requires a specific run-time but even native code may be dependent on underlying libraries contained within middleware (i.e. VC runtimes, java.) Microsoft coined the term “Managed Code” to describe code that requires the .NET Common Language Runtime (CLR.) It is written in .NET languages such as C# or Visual Basic .NET. Managed code’s memory, reference counting, and garbage collection is done by the underlying run-time – hence the term managed.

Native code refers to the classic Windows code that has been written in C, C++, Visual basic, and others in rare cases. While native code can easily be debugged through classic debuggers, managed code requires additional extensions. Native code is compiled to work directly with the underlying operating system while managed code is precompiled and then processed by the JIT (Just-in-time) .NET compiler and converted to native code at run-time allowing for greater portability. Native code was actually compiled for the operating system and hardware architecture. Porting this code to other architectures requires re-compiling.

Situation 1: Application Crashes

When an application crashes, it stops – immediately. Data is lost. It’s dead. It usually happens because the application has an encountered an unexpected exception and the potential for the exception has not been anticipated therefore the exception is not able to be properly handled within the application. Because of this, a special program within the operating system must deal with the aftermath. How the crash is intercepted and handled will depend on specific configurations within the operating system. How much data (active memory snapshots) that are actually saved for diagnostics also varies on how things are configured. Whether the module is native code or managed code will also potentially affect how it is handled.

Native Code Unexpected ErrorsExceptions

Depending on the operating system, when a normal application crashes, you will be interrupted with a dialog telling you that the application has stopped working and will be closed. Older users of windows may recognize the older 16-bit Windows blue screen that stated this. In recent versions of Windows (Windows Vista) and later WER (Windows Error Reporting) kicks in and cleans up the virtual address space and makes a record of the information even collecting a basic mini-dump. You will see a message like the one below.

WER is the modern version of an older program which would collect basic diagnostic data and a mini-dump. This program was called Dr. Watson and has been around since the dawn of Windows. WER takes this a step further and can report the crash to Microsoft. This is especially helpful if the program crashing is a Microsoft application. Other ISV’s often incorporate JIT’s (just-in-Time) debuggers to collect information for their diagnostic purposes as well.

Developers, Support Technicians, and Diagnostic Engineers will often register an alternative JIT debugger to intercept an application crash. Often times this is so they can do live debugging, or substitute their preferred collection tool for collecting user mode dump files for further debugging. For example, if you have either Windows Debugger (WINDBG) installed or Visual Studio, you will see this instead:


Note that in the above example, the debugger is able to intercept at the exception point (just in time) so there could even be further live/step-through debugging done.

The Windows Error Reporting model ( is really a newer generation of what was formerly Dr. Waston in that it integrates with Microsoft for diagnostic and troubleshooting telemetry data called Software Quality Management (or SQM) data. WER defaults to collect SQM data and minidumps, but can easily be managed centrally, especially through GPOs. By default, minimal data is collected in the realm of user mode dumps and the dump files go into a special queue for upload to microsoft or potential another central repository.


You can configure WER to generate bigger dumps that can be more useful when debugging application crashes. You must provide some additional configuration to WER. Since I usually use this as a temporary measure (where I cannot install additional tools) I usually remove these once I have the data that I need.

First, create a folder where the dumps will be stored out of band from the WER queue (i.e. C:dumps.) Then import the below text as a .reg file:

Windows Registry Editor Version 5.00

 [HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsWindows Error ReportingLocalDumps]




Alternatively, you could also batch this out as well:

mkdir C:Dumps

reg add "HKLMSOFTWAREMicrosoftWindowsWindows Error ReportingLocalDumps" /f

reg add "HKLMSOFTWAREMicrosoftWindowsWindows Error ReportingLocalDumps" /v DumpType /t REG_DWORD /d 2 /f

reg add "HKLMSOFTWAREMicrosoftWindowsWindows Error ReportingLocalDumps" /v DumpCount /t REG_DWORD /d 100 /f

reg add "HKLMSOFTWAREMicrosoftWindowsWindows Error ReportingLocalDumps" /v DumpFolder /t REG_EXPAND_SZ /d C:Dumps /f

Double-click the .reg file to import it into the registry. If you wish to change the path where dumps are stored, you can edit the following key to reflect the preferred location:   

HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsWindows Error ReportingLocalDumpsDumpFolder

Even when I use the above, I still have trouble collecting good dumps when dealing with virtual application crashes. Not to mention, in my case I often have Visual Studio and the Windows Debugger installed together. I prefer (and strongly) recommend that you use the Sysinternals tool PROCUMP ( to intercept application crashes to collect dumps for post-mortem debugging.

One great feature of ProcDump is that you can also configure it to override WER (and other debuggers) as the default debugger by registering it with the JIT Application Exception Debugger key (AEDebug) and also control where the user mode dumps are stored. Once that happens, you will then see ProcDump intercept and collect dumps by default when application crashes occur.


Managed Code Unhandled Exceptions

For .NET applications that encounter unhandled exceptions within managed code, you get a different experience. The runtime incorporates elements for this very type of thing giving the user a different option than what they would normally get with WER or the alternative registered with AEDebug.


Exception Handling

Since we have discussed the fact that many application crashes come from unhandled exceptions – often access violations or what it used to referred to – GP faults – let’s discuss actual exception handling and why it is important. Exception handling is literally what it means, a method through code of anticipating and controlling how these exceptions will be handled through special processes or something relatively easy to track (often through interface messages and/or logging.) One of the many reasons we have WER (and historically Dr. Watson) in Windows was to ensure that the operating system would have a last resort method of handling these issues. Every exception cannot be caught with programming and often, the usefulness of how it is handled will vary from developer to developer. 🙂

In early Windows, primarily the early days of Win32, one of the touted features was the capability of being able to leverage SHE (Structured Exception handling) in the Win32 API. I first read and learned about SEH again, from master Matt Pietrick back in the NT 4 days reading MSJ (the earlier version of MSDN magazine. To my excitement and amazement, the article is STLL available online and worth a read to this day ( Exception handling leverages trap and try/catch statements in most programming languages. Here is an implementation in its simplest form using native code (C++)




                              *lpstr = '';         


               __except (GetExceptionCode() == EXCEPTION_ACCESS_VIOLATION ?

                                                            EXCEPTION_EXECUTE_HANDLER :




               g.fHandledViolation = FALSE;                     



This exception would yield the following message but still allow the program to continue.



How exception levels differ

Whether the exception comes in the form of a popup window or is just simply logged into a file or to ETW, it is up to the programmer to ensure this. It is also up to the developer as to the level of information that will be collected. To use a managed code example, the following exception handler will sufficiently catch the exception:








            catch (Exception e)


                Console.WriteLine("ERROR: Unexpected error.");

                Console.WriteLine("DETAILS: {0}", e.Message);

                return 3;



But the example below would serve even better as it would give more diagnostic information for troubleshooting:








            catch (Exception e)


                Console.WriteLine("ERROR: Unexpected error.");

                Console.WriteLine("EXECPTION TYPE: {0}", e.GetType().Name);

                Console.WriteLine("DETAILS: {0}", e.Message);

                Console.WriteLine("STACKTRACE: {0}", e.StackTrace);

                return 3;



This will log more detailed information including a trace of the current thread stack. Not sure what “Stack Trace” means? Do not worry, that will be covered in a later post.


Situation 2: Hangs

When an application hangs, you can break into the process using a debugger or you can use a debugging utility to save the existing data in memory into a dump file for post-mortem analysis. Windows has a similar mechanism for user mode hangs as it does for application crashes using WER. With WER, you are often given options to either wait, close the program and destroy the hung memory space, or capture a small dump and upload it to Microsoft to see if it is possibly a known issue with even perhaps a known solution.


In the case of virtual application, the data collected can often be unreliable so in place of using WER, I will use WinDBG or ProcDump to collect a hang dump for further analysis.


Situation 3: Heap Corruption

Another type of issue that can happen often with virtual applications is Heap Corruption. The Process heap is a special section of usable memory that is initially created when a process is created. The size is determined the linking portion of the compiler. Subsequent heaps may be created allocated, deallocated, and destroyed throughout the life of a process. With managed code, the heap is managed by the runtime (.NET CLR) to allocate objects and to provide its memory services like for example the Garbage Collector.


Heap corruption usually occurs when a process allocates a block of heap memory of a given size and then a thread writes to and/or frees memory addresses beyond the requested size of the heap block. Heap corruption can also occur when a process writes to block of memory that has already been freed.  Sometimes it is pretty obvious and the debugger is able to quickly assess it

0xc0000374 – A heap has been corrupted.

Usually during a heap API operation on the thread stack:


77b888c8 77b15c49 ntdll!RtlpFreeHeap+0x59c49

77b888cc 77abb4c8 ntdll!RtlFreeHeap+0x268

77b888d0 76eecb60 kernelbase!GlobalFree+0xc0

77b888d4 7796cd18 kernel32!GlobalFreeStub+0x28

77b888d8 000a1871 shttyapp!CorruptDatHeap+0xd1

77b888dc 000a2525 shttyapp!WndProc+0x345

77b888e0 777d84f3 user32!_InternalCallWinProc+0x2b

77b888e4 777b6c40 user32!UserCallWinProcCheckWow+0x1f0

77b888e8 777b6541 user32!DispatchMessageWorker+0x231

77b888ec 777d6f30 user32!DispatchMessageA+0x10

77b888f0 000a1242 shttyapp!WinMain+0x152

77b888f4 000a2c19 shttyapp!__tmainCRTStartup+0x11a

77b888f8 779638f4 kernel32!BaseThreadInitThunk+0x24

77b888fc 77ae5e13 ntdll!__RtlUserThreadStart+0x2f

77b88900 77ae5dde ntdll!_RtlUserThreadStart+0x1b


Most of the time, you have to incorporate more specific tools to track it down. Speaking of that:


Next up: more on the tools!

MED-V V2: How to Enable Advanced Logging

In MED-V V2 all events logs are stored on the MED-V Host (Windows 7) and the MED-V Guest (Windows XP) using the “MEDV” event log. By default the event logs are set to Error and Warning events. Additional Debug level logging can be enabled via the registry in both the guest and the host by navigating to
the following key on both the host and the guest:


Set the “EventLogLevel” value to “4”

(You will need to create this value as a DWORD value.)

This can be enabled on both the host and the guest operating systems. Once enabled, all Debug events are listed in the MED-V event log with an Event ID of “0.”

The event logs on the Host can be used to troubleshoot problems with the MED-V Host engine such as URL redirection. The event logs on the guest can be used to troubleshoot the MED-V services running in the Windows XP operating system. It is recommended to enable this on both operating systems
when troubleshooting elements such as host network printer redirection and URL redirection.

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Important notice for those of you building C++ projects with App-V virtualized Visual Studio 2008 . . .

March 31, 2011 1 comment

. . . if you build it with debugging enabled it will not complete and will throw an error in the console window.

When using a virtualized instance of Visual Studio (sequenced following the instructions at

When users build a C++ project in Visual Studio 2008 with debugging enabled the compiled program will not run and gives an error in the console window and/or the interface.

ERROR in Visual Studio Interface:

 “Unable to start program ‘path_to_program\program_name.exe’.”

“This application has failed to start because the application configuration is incorrect. Review the manifest file for possible errors. Reinstalling the application may fix this problem. For more details, please see the application event log.”

ERROR in console window:

“The system cannot execute the specified program.”

[To reproduce this specifically:

Create a new empty C++ project in Visual Studio. Write any compilable and runable code. Build the project (F7). Run the project without debugging (CTRL+F5) ]

 This problem does not occur when the project is set to release mode – only in debug mode.

This is caused by the debug run-time modules not being captured inside the virtual application package because of how the Application Virtualization side-by-side process works during sequencing. The debug runtimes are not used, so they are left out.

In order to work around this, the developer will need to install the debug runtimes on the local machine. They can be built out of Visual Studio 2008 pretty easily as follows:

 1. From Visual Studio, navigate to “File” – “New” – “Project.”

2. Select and expand “Other Project Types,” then “Setup and Deployment.”

3. In the Visual Studio Templates area, select “Setup Project.” Click “OK.”

4. In the Project window, Right-click “Setup1” and select “Add” – “Merge Module.”

5. Select all debug runtimes desired from the list.

6. Click Open

7. Right-click Setup1 and select “Build.”

8. Execute the project. It will install the modules you selected.