[Sjord]

malloc(0) may return NULL. Prevent it by allocating at least one byte. Otherwise PHP may think the system is out of memory because malloc returns NULL.

[devnexen]

The only unknown would be the more exotic platforms e.g. solaris/AIX. The change is probably not enough regardless.

Edit: indeed realloc case needs to be taken in account too.

[Sjord]

Yes, I came to this by trying it on AIX. There malloc(0) returns NULL.

__zend_realloc already sort-of handles it:

ZEND_API void * __zend_realloc(void *p, size_t len ZEND_FILE_LINE_DC ZEND_FILE_LINE_ORIG_DC)
{
	p = realloc(p, len);
	if (EXPECTED(p || !len)) {
		return p;
	}
	zend_out_of_memory();
}

So when p == NULL && len == 0 it returns NULL, and does not assume it's out of memory. However, even calling realloc(..., 0) is undefined behavior in C23, so technically this is incorrect.

[devnexen]

in that case, can this test be added ?

+--TEST--
+Zero-size reallocations with the tracked allocator
+--EXTENSIONS--
+zend_test
+--ENV--
+USE_ZEND_ALLOC=0
+USE_TRACKED_ALLOC=1
+--FILE--
+<?php
+var_dump(zend_test_erealloc_block_size(16, 0));
+var_dump(zend_test_erealloc_block_size(16, 0));
+?>
+--EXPECT--
+array(2) {
+  [0]=>
+  int(1)
+  [1]=>
+  int(1)
+}
+array(2) {
+  [0]=>
+  int(1)
+  [1]=>
+  int(1)
+}