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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


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