Re: RFC: more detailed type information

[Greg Watson <g.watson@computer.org>]

On Mar 28, 2006, at 3:36 PM, Daniel Jacobowitz wrote:

> On Thu, Mar 09, 2006 at 12:49:23PM -0700, Greg Watson wrote:
>> I'm using Eclipse as a front-end for gdb, but I need to be able to
>> get more detailed type information than is currently possible. This
>> is required in order to provide more sophisticated functionality than
>> just displaying the type and value as strings.
>
> Hi Greg,
>
> Can you be a little more detailed about what you need from GDB?
> There've been several mentions of this functionality recently,
> and I'm nearly positive that Apple's GDB supports something similar,
> so it's clearly a good idea.  However, what you have is a very thin
> layer around GDB's type system, which makes it hard to change the type
> system at all without simultaneously changing the MI interface.  I'd
> like to know what information is really useful.
>
> With C, of course, it doesn't much matter: the underlying type system
> can be simple because the language type system is simple.  But with
> other supported languages this can be much harder.
>
> And, no offense, but the ref=/seen= interface is nasty!  Maybe we
> should give types session UIDs.
>

Hi Daniel,

What I'm after is a language independent type description that  
provides enough information to allow the manipulation of program data  
in an external framework. For example, I'd like to be able to compare  
(subtract) all the elements of two arrays of floating point numbers.  
I have already implemented this infrastructure for type and value  
representation, but it's limited by the information that can be  
obtained via the current MI interface. Since gdb maintains this type  
information internally, I was hoping to provide a more complete,  
efficient, and language independent means of accessing the information.

The information that I need includes the endianness and size of  
simple types, and the type description and layout of complex types.  
While the representation I'm using is not a complete one-to-one  
mapping with the memory layout in the target (I don't preserve  
padding in structures for example) it is a fairly accurate  
representation of the object. Currently I support all C and Fortran  
types, a subset of C++ (I'm only interested in data, so methods and  
virtual types are not currently implemented), Pascal strings, and a  
few other odds and ends. Adding support for a new type is not  
particularly difficult.

I'd be very happy with a gdb interface that prints the type  
description directly in my format :-) I actually wrote the code to do  
this a few years ago but I thought this would not be of interest to  
others, which is why I was suggesting using the gdb type  
descriptions.  Are you expecting the type system to change? I've been  
working with gdb for many years and, apart from new language  
features, there seems to have been little change in this area.

I wasn't aware that the Apple GDB supported something like this. I'll  
take a look to see if it could provide the information I'm after.  
Would this be a more acceptable way to go?

LOL, I don't have any attachment to the ref/seen interface. If you  
can think of a better way to deal with recursive type definitions, I  
would love to know!

Regards,

Greg