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Re: stack overflow in regexp matcher with gdb

From: Stefan Monnier
Subject: Re: stack overflow in regexp matcher with gdb
Date: Thu, 14 Nov 2013 14:31:06 -0500
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3.50 (gnu/linux)

> I tried with the 24.3 version of emacs and the gdb -i=mi interface. It seems
> it works a little bit better (doesn't fail with that kind of error). However
> when I do a "next" the first one is ok but the second "next" is very slow
> and then it's ok again and then it's very slow again, etc... and from time
> to time the gdb prompt is no longer printed even though I can still enter
> gdb commands... 

Hmm... performance bugs can be even worse to track down :-(

> Using gud-gdb with the 24.3 version of emacs seems even more weird as it
> doesn't show the source files I've stop in...

That's odd as well: for me it does jump to the source.  `gud-gdb' should
be the "safe fallback", so please report a bug about this, providing as
much details as you can.

>   looking-at(",value=\\(\".*\"\\).*?}")

Indeed, this regexp is problematic.  Do you have some idea what the text
can be between the quotes?
IOW can we use (looking-at ",value=\\(\"[^\"]*\"\\).*?}") instead
(which would eliminate the backtracking), or is the a risk of the value
containing a " somewhere (and if so, how is it quoted?)?

The 24.3 code is pretty different, but I see the same kind of regexp, so
the same problem is probably present as well.


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