Re: Python, pretty printing, frame decorators and MI

On 2017-06-15 00:06, Jan Vrany wrote:
> Hi there,
> 
> to ease debugging, I have a set of python pretty printers and frame
> decorators - they work fine and print internal structures nicely.
> 
> I also have a custom frontend using MI. I want to reuse these python
> printers / decorators in the frontend. This way I don't need to
> duplicate the code of pretty printer on top of MI.
> 
> The problem is that if I enable pretty printing / frame filters in MI,
> I no longer get the "raw" values, only pretty printed.
> 
> For example, let's say I have a pretty printer for type OBJ (pointer to
> a struct) which prints "0x12345678 (Symbol: #x:y:)" while without
> pretty printer it would just print "0x12345678". 
> Similar happens for frame decorators. Once I enable frame
> filters/decorators, I no longer have access (on MI level) to raw
> function name as in DRARF debug info.
> 
> How difficult would be to extend MI to provide both representations? 
> The idea is to provide another "property" with "raw" represenstation.
> This way it'd be backward compatible as MI frontends are expected to
> ignore unknown properties.
> 
> Could you give me some pointers/hints where to look GDB code in order
> to (try to) add this functionality?

I don't know if it's already possible to get what you want, if it is 
perhaps somebody else will reply with an answer.

Otherwise, it shouldn't be too difficult to prototype the functionality 
you are describing.  If you are interested in modifying the output of 
the -var-evaluate-expression command, for example, start at 
mi_cmd_var_evaluate_expression in mi/mi-cmd-var.c and follow the code 
from there.

I can't tell you what's the best design for this (because I don't know 
the answer :)).  I think the best way to proceed is to try some things 
on your side, come up with a concrete proposal of the changes you'd like 
to bring, and then we can discuss about that.

> Would it be also possible to allow Python to define new MI commands in
> addition to CLI commands?

I think it would be a very cool feature.  There was a submission to 
implement that by Didier Nadeau:

   https://sourceware.org/ml/gdb-patches/2017-02/msg00283.html

I think it's also available here if you want to try it:

   https://github.com/nadeaud/binutils-gdb/commits/python-mi

I don't know if Didier will have time to follow-up with it, I added him 
in CC so he can reply himself.  If he doesn't plan to follow-up, and you 
want to pick up where he left off, I'm sure there will be no problem.

Thanks,

Simon