Do not create the opcache shm mapping too close to the end of the heap

Under some conditions we may create the opcache shm segment just after the
heap, which prevents it from expanding. Memory allocators may fallback to
mmap(), but this may confuse some (unidentified) code.

Author: arnaud-lb

ext/opcache/shared_alloc_mmap.c

@@ -20,6 +20,7 @@
 */
 
 #include "zend_shared_alloc.h"
+#include "jit/zend_jit.h"
 
 #ifdef USE_MMAP
 
@@ -45,7 +46,7 @@
 # define MAP_HUGETLB MAP_ALIGNED_SUPER
 #endif
 
-#if (defined(__linux__) || defined(__FreeBSD__)) && (defined(__x86_64__) || defined (__aarch64__)) && !defined(__SANITIZE_ADDRESS__)
+#if defined(HAVE_JIT) && (defined(__linux__) || defined(__FreeBSD__)) && (defined(__x86_64__) || defined (__aarch64__)) && !defined(__SANITIZE_ADDRESS__)
 static void *find_prefered_mmap_base(size_t requested_size)
 {
 	size_t huge_page_size = 2 * 1024 * 1024;
@@ -188,8 +189,17 @@ static int create_segments(size_t requested_size, zend_shared_segment ***shared_
 #ifdef PROT_MAX
 	flags |= PROT_MAX(PROT_READ | PROT_WRITE | PROT_EXEC);
 #endif
-#if (defined(__linux__) || defined(__FreeBSD__)) && (defined(__x86_64__) || defined (__aarch64__)) && !defined(__SANITIZE_ADDRESS__)
-	void *hint = find_prefered_mmap_base(requested_size);
+#if defined(HAVE_JIT) && (defined(__linux__) || defined(__FreeBSD__)) && (defined(__x86_64__) || defined (__aarch64__)) && !defined(__SANITIZE_ADDRESS__)
+	void *hint;
+	if (JIT_G(enabled) && JIT_G(buffer_size)
+			&& zend_jit_check_support() == SUCCESS) {
+		hint = find_prefered_mmap_base(requested_size);
+	} else {
+		/* Do not use a hint if JIT is not enabled, as this profits only JIT and
+		 * this may be unsafe when the hole after the heap is the only candidate
+		 * (e.g. in non-PIE builds) (GH-13775). */
+		hint = MAP_FAILED;
+	}
 	if (hint != MAP_FAILED) {
 # ifdef MAP_HUGETLB
 		size_t huge_page_size = 2 * 1024 * 1024;