Extending a debugger for data inspection and visualization

[Manoj Rajagopalan]

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Subject: Extending a debugger for data inspection and visualization
Date: Friday 24 July 2009
From: Manoj Rajagopalan <rmanoj at umich.edu>
To: KDevelop Developer Mailinglist <kdevelop-devel at barney.cs.uni-potsdam.de>

Hi Niko, Vladimir, Andreas and others,

  I looked up kdevplatform/debugger/variable/variablecollection.{h,cpp}. 
Please confirm if I understand the following points. Then please help me with 
my questions that follow.

* the classes there are treeitems that will appear in the variable-widget's 
variable tree.

* There seem to be two principal categories right now : locals and watches. 

* There used to be a third category of evaluated expressions under 
the "Recent" tree header item in KDev3 but it has probably been absorbed into 
one of the above or will be generated when the user requests one for the 
first time.

QUESTIONS:

* Data inspection nodes like visualization and memory tables will be special 
kinds of expressions which require reading arrays of data from memory. Will 
we need a new subclass of Variable or TreeItem to handle these?

* Can these nodes be given a separate heading like "Data Inspection" which 
appears as a sibling to Locals and Watches? While these behave as 
expressions, they won't exactly be expressions because they may require 
auxiliary user-data to function. For example, a "complex<double> matrix" view 
of memory will require additional information like whether the data is laid 
out in row-major or column-major formats and the stride between rows or 
columns in either case.

* In KDev3 there was a memory-viewer widget which allowed examination of a hex 
dump of memory. A data-inspection widget is the generalization where we can 
view memory according to some schema (like a structure) given the starting 
address, schema and layout information. At the outset this is easy to achieve 
with simple types like int, float, double etc. that extend the basic view of 
memory as bytes. Does this seem like a useful feature?

* Tabulation or graphing of data is a matter of representation and therefore 
we have a MVC paradigm here. Because of the debugger abstraction, can all 
this be folded into a debugger-independent plugin? If so what classes and 
methods should I begin looking at to extract the relevant information from 
the debugger? I have noticed that IDebugController returns a 
VariableCollection*. Once I setup a slot to receive its 
sessionAdded(KDevelop::IDebugSession*) signal, I should be able to get all 
this information from VariableCollection, correct? From this I can list 
various variable objects but how do I go about evaluating them and extracting 
array data? In the case of strided-data I will need multiple calls to the 
debugger to retrieve data-set pieces which I will then need to assemble 
together form a coherent data-model.

Thanks,
Manoj



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