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https://github.com/microsoft/DbgShell

A PowerShell front-end for the Windows debugger engine.
https://github.com/microsoft/DbgShell

debugger debugger-extension debugging windbg

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A PowerShell front-end for the Windows debugger engine.

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README 

        
# DbgShell

A PowerShell front-end for the Windows debugger engine.



Ready to tab your way to glory? For a quicker intro, take a look at [Getting

Started](doc/GettingStarted.md).



[![Build status](https://ci.appveyor.com/api/projects/status/h5ejj6kpyn2tjdat/branch/master?svg=true)](https://ci.appveyor.com/project/jazzdelightsme/dbgshell/branch/master)



## Disclaimers



1. This project is not produced, endorsed, or monitored by the Windows debugger team.

   While the debugger team welcomes feedback about their API and front ends (windbg, kd,

   et al), they have no connection with this project. Do not file bugs or feedback to the

   debugger team concerning this project.



2. This is not a funded project: it has no official resources allocated to it, and is only

   worked on by volunteers. Do not take any production dependency on this project unless

   you are willing to support it completely yourself. Feel free to file Issues and submit

   Pull Requests, but understand that with the limited volunteer resources, it may be a

   while before your submissions are handled.



3. This is an experimental project: it is not fully baked, and you should expect breaking

   changes to be made *often*.



Corollary of above disclaimers: I would avoid attaching DbgShell to live targets of high value.



## Binaries



[https://aka.ms/dbgshell-latest](https://aka.ms/dbgshell-latest)



## Motivation



Have you ever tried automating anything in the debugger? (cdb/ntsd/kd/windbg) How did that

go for you?



The main impetus for DbgShell is that it's just waaaay too hard to automate anything in

the debugger. There *are* facilities today to assist in automating the debugger, of

course. But in my opinion they are not meeting people's needs.

* Using the built-in scripting language is arcane, limited, difficult to get right, and

  difficult to get help with.

* Writing a full-blown debugger extension DLL is very powerful, but it's a significant

  investment—way too expensive for solving quick, "one-off" problems as you debug random,

  real-world problems. Despite the cost, there are a large number of debugger extensions

  in existence. I think there should not be nearly so many; I think the only reason there

  are so many is because there aren't viable alternatives.

* Existing attempts at providing a better interface (such as

  [PowerDbg](http://powerdbg.codeplex.com/)) are based on "scraping" and text parsing,

  which is hugely limiting (not to mention ideologically annoying) and thus are not able

  to fulfill the promise of a truly better interface (they are only marginally better, at

  best).

* Existing attempts to provide an easier way to write a debugger extension are merely a

  stop-gap addressing the pain of developing a debugger extension; they don't really solve

  the larger problem. (for instance, two major shortcomings are: they are still too

  low-level (you have to deal with the dbgeng COM API), and there's no REPL)

* The debugger team has recently introduce [Javascript

  scripting](https://docs.microsoft.com/en-us/windows-hardware/drivers/debugger/javascript-debugger-scripting).

  Javascript is a much better (and more well-defined) language than the old windbg

  scripting language, but I think that PowerShell has some advantages, the largest of

  which is that nobody really uses a Javascript shell--PowerShell is much better as a

  combined shell *and* scripting language.



**The goal of the DbgShell project is to bring the goodness of the object-based PowerShell

world to the debugging world.** When you do 'dt' to dump an 'object', you should get an

*actual* object. Scripting should be as easy as writing a PowerShell script.



The DbgShell project provides a PowerShell front-end for dbgeng.dll, including:

* a managed "object model" (usable from C# if you wished), which is higher-level than the

  dbgeng COM API,

* a PowerShell "navigation provider", which exposes aspects of a debugging target as a

  hierarchical namespace (so you can "cd" to a particular thread, type "dir" to see the

  stack, "cd" into a frame, do another "dir" to see locals/registers/etc.),

* cmdlets for manipulating the target,

* a custom PowerShell host which allows better control of the debugger CLI experience, as

  well as providing features not available in the standard powershell.exe host (namely,

  support for text colorization using ANSI escape codes (a la [ISO/IEC

  6429](http://en.wikipedia.org/wiki/ISO/IEC_6429)))



The custom host is still a command-line (conhost.exe-based) program (analogous to

ntsd/cdb/kd), but it can be invoked from windbg (`!DbgShell`).



In addition to making automation much easier and more powerful, it will address other

concerns as well, such as ease of use for people who don't have to use the debuggers so

often. (one complaint I've heard is that "when I end up needing to use windbg, I spend all

my time in the .CHM")



For seasoned windbg users, on the other hand, another goal is to make the transition as

seamless as possible. So, for instance, the namespace provider is not the only way to

access data; you can still use traditional commands like "`~3 s`", "`k`", etc.



## What do you mean by "automation" and "scripting"?

I'm not _only_ talking about the sort of thing where you open up a text editor and write

some big script to do something complex—I'm _also_ talking about being able to whip out

relatively simple stuff directly on the command line. There are many situations where you

would like to be able to use a little bit of logic, but nothing so big or re-usable that

you would even want to save it. It should be easy to just whip off "one-liners" like

"break on CreateFile if the file being opened is on the user's desktop and function Blah

is on the stack."



## Why PowerShell?



Let me be clear: it took me approximately 4 years to "warm up" to PowerShell. I feel it

has sharp edges, aspects that are just plain difficult, and plenty of bugs, both in design

and implementation. Sometimes it really irritates me. *However,* the benefits of

PowerShell are compelling, and have convinced me that it's the best thing to use for this

project:



* It is both a scripting environment and a CLI environment. The fact that it has to do

  both leads to some negative things like a steeper learning curve, but in the end it is

  extremely handy, because you want to be able to both do stuff quickly in a command-line

  REPL, as well as write full-featured, robust scripts.

* It is very discoverable—things like `Get-Command`, tab completion, the ability to expose

  hierarchical data like a filesystem, the facilities for providing and synthesizing help,

  are very good.

* Tab completion. I know I mentioned it in the previous bullet, but it's awesome enough to

  get its very own bullet.

* The object pipeline: the object-oriented nature of the PowerShell pipeline is so much

  more powerful and easy to use than the bad old days of string-parsing-based scripting

  that it's not even funny. Imagine doing "`dt`" to "dump" an "object", and actually

  getting an object. DbgShell does that.

* People know it: I estimate that the number of people who know PowerShell and/or C# is at

  least a handful of orders of magnitude larger than the people who know windbg scripting

  techniques. That means more people will be able to easily "pick up" a PowerShell-based

  debugger; and it also means that when people need help, the pool of potential helpers is

  much larger (for scripting-related issues, anyway).

* PowerShell is still a general-purpose shell: when using DbgShell, you have access to not

  just debugger commands, but you can "`cd`" over to the filesystem, registry, AD, etc.;

  you can execute `Send-MailMessage`, `Get-WmiObject`, `Invoke-WebRequest`,

  `Invoke-RestMethod`, run arbitrary programs, etc.



## Current Status



DbgShell has been in "prototyping mode" for a long time. I have spent a lot of time

figuring how something could or should be done, but not necessarily "finishing"

everything. There are a huge number of TODOs in the current code. So although it has

started to become actually useful, the project is still pretty green. However, it can

definitely demonstrate enough to give you a good taste of what it should be like.



Below are some screenshots. It's important to note that nothing you see is dbgeng text

output. Although some stuff in the output will look familiar, that is only because I have

used PowerShell's formatting and output features to customize how certain objects are

displayed—all the output you see actually corresponds to real, full .NET objects. For

instance, those ModLoad messages each correspond to a `MS.Dbg.ModuleLoadedEventArgs`

object, which has more properties than what get displayed when sent to `Out-Default`.

There is no string parsing of anything from dbgeng whatsoever. (Well... almost. I've made

a few compromises where there is no other way to get information. For instance,

disassembly stuff, or parsing the symbolic name of an adjustor thunk function to find the

offset.)



This is a sort of "hello world" scenario: attaching to an instance of cmd.exe. I first use

the PowerShell built-in command `Start-Process`, then pipe the output to the DbgShell

command `Connect-Process`, and then poke around the namespace:



![Hello DbgShell](doc/screenshot_01.png)



Here I have attached to a test program, and looked at the stack, switched to a particular

stack frame, dumped locals, inspected the value of a local `std::map`, and inspected some

type information for a local enum value. Note the display of the enumeration value: not

only does DbgShell handle looking up the symbolic name for single enumerands, but also

when multiple enumerands are OR'ed together. You can't tell this from the screenshot, but

there is tab completion for all of this stuff.



![tbd](doc/screenshot_02.png)



## Notable Features

* [Color](doc/Color.md): support for text colorization using ANSI escape codes (a la

  [ISO/IEC 6429](http://en.wikipedia.org/wiki/ISO/IEC_6429))

* [Custom formatting engine](doc/CustomFormattingEngine.md): Don't like .ps1xml stuff? Me

  neither. In addition to standard table, list, and custom views, you can define

  "single-line" views which are very handy for customizing symbol value displays.

* [Custom symbol value conversion](doc/SymbolValueConversion.md): For most variables, the

  default conversion and display are good. But sometimes, you'd like the debugger to do a

  little more work for you. The symbol value conversion feature allows, for instance, STL

  collection objects to be transformed into .NET collection objects that are much easier

  to deal with.

* [Derived type detection](doc/DerivedTypeDetection.md): For when your variable is an

  IFoo, but the actual object is a FooImpl.

* [Rich type information](doc/RichTypeInfo.md): exposed for your programmatic pleasure.

* **Q:** Does it work in WinDbg? I will only use WinDbg. **A:** Yes--load up the

  DbgShellExt.dll extension DLL, and then run "`!dbgshell`" to pop open a DbgShell

  console.



## Current Deficiencies

* The biggest deficiency currently is that it does not support kernel mode well (if you

  are already in the proper context, you can display values, but you can't change context

  from within DbgShell, and the namespace is not wired up).

* Although you can load and execute traditional debugger extensions in the usual way,

  there are still many windbg commands missing.

* Remotes are not supported: the dbgeng API supports connecting to a remote debugger.

  Unfortunately, the symbol and type information exposed by the dbgeng API is critically

  insufficient for DbgShell's needs, so DbgShell uses the dbghelp API. Unfortunately,

  there is no such thing as remote dbghelp. We will need to work with the debugger team to

  solve this problem.



## License

Licensed under the [MIT](License.txt) License.



## Contributing



This project welcomes contributions and suggestions. Most contributions require you to

agree to a Contributor License Agreement (CLA) declaring that you have the right to, and

actually do, grant us the rights to use your contribution. For details, visit

https://cla.microsoft.com.



When you submit a pull request, a CLA-bot will automatically determine whether you need to

provide a CLA and decorate the PR appropriately (e.g., label, comment). Simply follow the

instructions provided by the bot. You will only need to do this once across all repos

using our CLA.



See [Contributing](Contributing.md) for more information about contributing to the project.



## Code of Conduct



This project has adopted the [Microsoft Open Source Code of

Conduct](https://opensource.microsoft.com/codeofconduct/).



For more information see the [Code of Conduct

FAQ](https://opensource.microsoft.com/codeofconduct/faq/) or contact

[[email protected]](mailto:[email protected]) with any additional questions or

comments.



## Other topics

* [Getting Started with DbgShell](doc/GettingStarted.md)

* [Color](doc/Color.md)

* [Custom formatting engine](doc/CustomFormattingEngine.md)

* [Custom symbol value conversion](doc/SymbolValueConversion.md)

* [Derived type detection](doc/DerivedTypeDetection.md)

* [Rich type information](doc/RichTypeInfo.md)



* [Hacking on DbgShell](Contributing.md)



* [DbgEngWrapper](doc/DbgEngWrapper.md)



You can find a short (3 minute) video introduction here: https://youtu.be/ynbg2zZ1Igc