Fix GH-23088: Stack overflow when comparing deeply nested arrays

[lazerg]

Comparing two deeply nested arrays recurses through zend_compare_arrays -> zend_compare_symbol_tables -> zend_hash_compare once per nesting level, and nothing bounds that recursion. zend_hash_compare() only guards against cycles, so a non-cyclic array a few tens of thousands of levels deep runs the C stack out and the process dies with a segfault. === crashes the same way through zend_is_identical().

Both now check the stack limit before descending and throw an Error instead, the same way zend_std_compare_objects() already handles the object case.

Fixes GH-23088

[arnaud-lb]

Is this one required, if zend_compare_arrays() checks it too?

[lazerg]

It was, yes. === goes zend_is_identical() -> zend_hash_compare() -> hash_zval_identical_function() -> zend_is_identical(), so it never passes through zend_compare_arrays(). Moot now anyway, both checks are gone and the one in zend_hash_compare() covers each path.

[arnaud-lb]

Since zend_hash_compare() does the nesting level check, I would prefer if the stack check was moved there as well. WDYT?

[lazerg]

Done, it now sits right next to the recursion guard in zend_hash_compare() and both copies are gone. One side effect: that function also handles object property tables and SplObjectStorage, so the message had to become generic ("Maximum call stack size reached during comparison"), which meant adjusting the regex in gh18572.phpt.