Hi internals, We have a long-standing issue (tracked at https://bugs.php.net/bug.php?id=64196 and the very numerous duplicates) that certain types of infinite recursion can lead to a stack overflow. While for us it is easy to diagnose this, end users will only see a "segmentation fault" and will be unable to correlate this with infinite recursion as the root cause.
To provide some technical context, recursion in PHP usually occurs on the virtual machine stack, in which case unbounded recursion is supported, as long as the stack size does not exceed your memory limit. However, some types of calls (in particular magic methods and certain callbacks) go through an internal function and have to reenter the virtual machine. This uses up space on the C stack and may ultimately result in a stack overflow. I would like to propose the introduction of a zend.vm_reentry_limit ini option as a solution to this problem, implemented in https://github.com/php/php-src/pull/5135. This ini setting will limit the number of nested VM reentries that are allowed before an Error is thrown. It should be noted that this is (intentionally) not a general recursion limit. Deep recursion can happen legitimately (e.g. during AST processing) and it is hard to put a reasonable upper limit on it that both detects unintentional infinite recursion while allowing legitimate deep recursion. The limit implemented here exists specifically to prevent stack overflows and give the programmer a more obvious indication of the cause of the problem. Regards, Nikita PS: Some extensions will force all function calls to occur via VM reentry. Such extensions should probably either disable the option (by setting it to -1), or significantly increase the limit, to avoid false positives.
