Christoph Becker wrote: > Adam Harvey wrote: > >> On 23 July 2015 at 11:47, Christoph Becker <cmbecke...@gmx.de> wrote: >> <snip great explanation, thanks> >>> Therefore I tend to prefer a new ini setting (say, pcre.jitstack_limit). >>> That would mean, however, to add yet another ini setting, of which >>> there are already so many. >> >> I'm not a big fan of that, although it's at least in the spirit of >> what configuration settings are meant to be used for. >> >> What if we added the PCRE_ERROR_JIT_STACKLIMIT error constant to those >> exposed to userland so that it's more easily noticed via >> preg_last_error(), and adding a modifier that can be used to disable >> the JIT on a per-pattern basis (by setting PCRE_NO_START_OPTIMIZE, >> which admittedly disables other stuff too, but at least the regex will >> run)? At least then users could check the error when the regex fails >> and re-run the regex without the JIT if they chose to. > > Yes, that would be an option. I'm not sure if we need to touch > PCRE_NO_START_OPTIMIZE (or if it would even help); simply not calling > pcre_study() respectively not passing the studied extra data (second > argument) to pcre_exec() should be sufficient.
Correction: we simply should not pass PCRE_STUDY_JIT_COMPILE to pcre_study() if we want to disable JIT support for individual regexps.[1] >> How likely is the average user to hit this, do you think? > > I don't know. The libpcre man pages say: > > | JIT uses far less memory for recursion than the interpretive code, > | and a maximum stack size of 512K to 1M should be more than enough for > | any pattern. > > Of course, a hard-coded 512K or even more would be rather much. The > default stack size (32K) for the regex in the test script of #70110 > would be sufficient, if the subject is repeated only about 2000 times, > but that doesn't say much (the preg_match() is rather contrived). > > Anyway, that shows that it's not only the pattern that's relevant for > the needed JIT stack space, but also the subject string. [1] <https://github.com/php/php-src/blob/php-7.0.0beta2/ext/pcre/php_pcre.c#L436-L440> -- Christoph M. Becker -- PHP Internals - PHP Runtime Development Mailing List To unsubscribe, visit: http://www.php.net/unsub.php
