Description:
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When a class is created which implements Serializable, and the serialize method instantiates another class which is then serialized and returned, and several instances of the first class are created in an array, and then entire array is serialized, instances after the first one are considered recursive. If this is unserialized, PHP segfaults.

Test script:
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https://gist.github.com/will-in-wi/7951652

If you uncomment the last line, the entire script segfaults.

Expected result:
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a:9:{i:0;C:10:"HelloWorld":39:{O:6:"Simple":1:{s:4:"test";s:4:"str1";}}i:1;C:10:"HelloWorld":4:{O:6:"Simple":1:{s:4:"test";s:4:"str2";}}i:2;C:10:"HelloWorld":4:{O:6:"Simple":1:{s:4:"test";s:4:"str3";}}i:3;C:10:"HelloWorld":4:{O:6:"Simple":1:{s:4:"test";s:4:"str4";}}i:4;C:10:"HelloWorld":4:{O:6:"Simple":1:{s:4:"test";s:4:"str5";}}i:5;C:10:"HelloWorld":4:{O:6:"Simple":1:{s:4:"test";s:4:"str6";}}i:6;C:10:"HelloWorld":4:{O:6:"Simple":1:{s:4:"test";s:4:"str7";}}i:7;C:10:"HelloWorld":4:{O:6:"Simple":1:{s:4:"test";s:4:"str8";}}i:8;C:10:"HelloWorld":4:{O:6:"Simple":1:{s:4:"test";s:4:"str9";}}}

Actual result:
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a:9:{i:0;C:10:"HelloWorld":39:{O:6:"Simple":1:{s:4:"test";s:4:"str1";}}i:1;C:10:"HelloWorld":4:{r:3;}i:2;C:10:"HelloWorld":4:{r:3;}i:3;C:10:"HelloWorld":4:{r:3;}i:4;C:10:"HelloWorld":4:{r:3;}i:5;C:10:"HelloWorld":4:{r:3;}i:6;C:10:"HelloWorld":4:{r:3;}i:7;C:10:"HelloWorld":4:{r:3;}i:8;C:10:"HelloWorld":4:{r:3;}}