# PCRE and recursion: NO_RECURSE flag

- Thread: https://externals.io/message/39730
- Original archive: https://news-web.php.net/php.internals/39730
- Started by Arnaud Le Blanc on 2008-08-07T12:24:04+00:00
- Messages: 3
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## #39730 — Arnaud Le Blanc — 2008-08-07T12:24:04+00:00

URL: https://externals.io/message/39730#39730

Hi,

PCRE can be highly recursive [1] and this can cause segmentation faults [2]. 
This is a known problem and the pcre ini settings avoids the segfaults, but 
the execution of the expression will fail anyway.

PCRE has a NO_RECURSE flag which makes the match() internal function no 
recursive and avoids this problem. The configure switch for this option is --
disable-stack-for-recursion. NO_RECURSE is documented in pcre_exec.c.

This can be easily enabled [3] for the bundled PCRE. It seems to be safe to 
enable that. Actually the PCRE test suite pass with NO_RECURSE enabled, and 
segfaults without. Can this be enabled ?

[1] http://manpages.courier-mta.org/htmlman3/pcrestack.3.html
[2] http://bugs.php.net/bug.php?id=45735
[3] http://arnaud.lb.s3.amazonaws.com/pcre_no_recurse.patch

Regards,

Arnaud

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## #39731 — Nuno Lopes — 2008-08-07T12:35:12+00:00

URL: https://externals.io/message/39730#39731 · In reply to: #39730

No!
Last time I benchmark it, it has about 100x slower, so I don't think so.. If 
you need to match large amounts of data, just increase the stack size. 
ulimit is your friend :)

Nuno


----- Original Message ----- 
From: "Arnaud Le Blanc" <arnaud.lb@gmail.com>
To: <internals@lists.php.net>
Sent: Thursday, August 07, 2008 1:24 PM
Subject: [PHP-DEV] PCRE and recursion: NO_RECURSE flag


> Hi,
>
> PCRE can be highly recursive [1] and this can cause segmentation faults 
> [2].
> This is a known problem and the pcre ini settings avoids the segfaults, 
> but
> the execution of the expression will fail anyway.
>
> PCRE has a NO_RECURSE flag which makes the match() internal function no
> recursive and avoids this problem. The configure switch for this option 
> is --
> disable-stack-for-recursion. NO_RECURSE is documented in pcre_exec.c.
>
> This can be easily enabled [3] for the bundled PCRE. It seems to be safe 
> to
> enable that. Actually the PCRE test suite pass with NO_RECURSE enabled, 
> and
> segfaults without. Can this be enabled ?
>
> [1] http://manpages.courier-mta.org/htmlman3/pcrestack.3.html
> [2] http://bugs.php.net/bug.php?id=45735
> [3] http://arnaud.lb.s3.amazonaws.com/pcre_no_recurse.patch
>
> Regards,
>
> Arnaud

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## #39732 — Arnaud Le Blanc — 2008-08-07T13:01:39+00:00

URL: https://externals.io/message/39730#39732 · In reply to: #39731

Sorry, I had not thought about that. I just checked with the example given in 
the bug report and it's effectively slower (~25% on this expression).

On Thursday 07 August 2008 14:35:12 Nuno Lopes wrote:
> No!
> Last time I benchmark it, it has about 100x slower, so I don't think so..
> If you need to match large amounts of data, just increase the stack size.
> ulimit is your friend :)
>
> Nuno
>
>
> ----- Original Message -----
> From: "Arnaud Le Blanc" <arnaud.lb@gmail.com>
> To: <internals@lists.php.net>
> Sent: Thursday, August 07, 2008 1:24 PM
> Subject: [PHP-DEV] PCRE and recursion: NO_RECURSE flag
>
> > […]