Description:
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Both PHP 5.2.0 (pcre 6.7) and 5.1.6 (pcre 6.6) have this problem:

A working pattern segfaults on certain user data. Could be stack overflow in pcre_exec/match.

This patterns is almost straight from the documentation:
/\{(?:(?>[^{}]+)|(?R))+\}/Us

Basically to match nested {} (instead of parentheses)

I found a simple workaround to the particular problem I have, but the code should not segfault.

Note if you change the 12000 in the code to anything less than 8158, it will produce the correct result.

Reproduce code:
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<?= preg_match('/{(?:(?>[^{}]+)|(?R))+}/Us',
    '{open'. str_repeat('.', 12000) .'{open}'), "\n"?>


Expected result:
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1

Actual result:
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Segmentation fault