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Date: Tue, 04 Aug 2015 13:15:46 +0200
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Subject: Re: [PHP-DEV] PCRE JIT stack size limit
From: cmbecker69@gmx.de (Christoph Becker)

Hi Anatol,

On 04.08.2015 at 11:24, Anatol Belski wrote:

> Hi Christoph,
> 
>> -----Original Message-----
>> From: Christoph Becker [mailto:cmbecker69@gmx.de]
>> Sent: Tuesday, August 4, 2015 2:35 AM
>> To: Anatol Belski <anatol.php@belski.net>; 'Christoph Becker'
>> <cmbecker69@gmx.de>; 'Pierre Joye' <pierre.php@gmail.com>
>> Cc: 'PHP internals' <internals@lists.php.net>
>> Subject: Re: [PHP-DEV] PCRE JIT stack size limit
>>
>> On 27.07.2015 at 13:28, Anatol Belski wrote:
>>
>>>> -----Original Message-----
>>>> From: Christoph Becker [mailto:cmbecker69@gmx.de]
>>>> Sent: Monday, July 27, 2015 12:06 AM
>>>> To: Anatol Belski <anatol.php@belski.net>; 'Pierre Joye'
>>>> <pierre.php@gmail.com>
>>>> Cc: 'PHP internals' <internals@lists.php.net>
>>>> Subject: Re: [PHP-DEV] PCRE JIT stack size limit
>>>>
>> If we leave it as this, I suggest to make pcre.jit PHP_INI_PERDIR instead of
>> PHP_INI_ALL for PHP 7.0.  That still gives users the option to disable it (ideally
>> even on shared hosting), but avoids issues when dynamically switching the
>> setting with regard to our regexp caching.  If we find a better solution for PHP
>> 7.1, we still can extend it to PHP_INI_ALL without a BC break.
>>
> That would disable possibility to change it in the registry which is PHP_INI_USER. That's something about shared hosting, too.

Ah, I see.  Then we ought to prominently document that chaning the
setting during script execution might not have the desired effect due to
internal caching.

>> For PHP 7.1 it might be worthwhile to consider to store jitted resp.
>> non-jitted regexps in the cache, and to fetch what fits to the current setting of
>> pcre.jit (and otherwise to compile again, adding the new entry to the cache, or
>> maybe replacing it).
>>
> Not sure to understand what you mean. Storing every pattern in both variants studied with and without JIT?

I didn't mean to store all patterns in both variants, but rather as
requested.  Say, the PHP script starts with pcre.jit=0, so all patterns
will be stored studied without JIT.  Then the script changes to
pcre.jit=1.  Following cache lookups check whether an already cached
pattern was studied with JIT.  If not, a new cache entry is made with
the pattern studied with JIT (that new entry may replace the old one or
not; not sure what's best).  Changing back to pcre.jit=0 will again keep
the old patterns, but ensures that only those which have been studied
without JIT are retrieved from the cache.

-- 
Christoph M. Becker