Mark strings as IS_STR_VALID_UTF8 on-the-fly

Alternative to GH-10870. Use atomic writes for adding the IS_STR_VALID_UTF8 flag
to UTF-8-verified interned strings in ext-mbstring. x86 and other architectures
guarantee atomic writes/reads for aligned variables up to size_t, which we
already rely on, particularly for zend_op.handler being swapped out in the JIT.
The atomic write is only needed here to not drop any other newly written bits
(which there currently aren't any of). We use GCC and sync atomics because they
don't require annotating the modified variable with the C11 _Atomic keyword.

Author: iluuu1994

ext/mbstring/mbstring.c

@@ -67,6 +67,28 @@
 
 #include "zend_simd.h"
 
+#include "ext/opcache/zend_shared_alloc.h"
+#include "ext/opcache/ZendAccelerator.h"
+
+static void mark_zstr_as_utf8(zend_string *s)
+{
+	if (!ZSTR_IS_INTERNED(s)) {
+		GC_ADD_FLAGS(s, IS_STR_VALID_UTF8);
+		return;
+	}
+
+	/* We don't use zend_atomic.h as we're writing to a non-_Atomic field. */
+#if (__GNUC__ == 4 && __GNUC_MINOR__ >= 7) || (__GNUC__ > 4)
+	SHM_UNPROTECT();
+	__atomic_or_fetch(&GC_TYPE_INFO(s), IS_STR_VALID_UTF8 << GC_FLAGS_SHIFT, __ATOMIC_SEQ_CST);
+	SHM_PROTECT();
+#elif defined(__GNUC__)
+	SHM_UNPROTECT();
+	__sync_or_and_fetch(&GC_TYPE_INFO(s), IS_STR_VALID_UTF8 << GC_FLAGS_SHIFT);
+	SHM_PROTECT();
+#endif
+}
+
 /* }}} */
 
 /* {{{ prototypes */
@@ -2263,8 +2285,8 @@ PHP_FUNCTION(mb_substr_count)
 		} else {
 			unsigned int num_errors = 0;
 			haystack_u8 = mb_fast_convert((unsigned char*)ZSTR_VAL(haystack), ZSTR_LEN(haystack), enc, &mbfl_encoding_utf8, 0, MBFL_OUTPUTFILTER_ILLEGAL_MODE_BADUTF8, &num_errors);
-			if (!num_errors && !ZSTR_IS_INTERNED(haystack)) {
-				GC_ADD_FLAGS(haystack, IS_STR_VALID_UTF8);
+			if (!num_errors) {
+				mark_zstr_as_utf8(haystack);
 			}
 		}
 
@@ -2273,8 +2295,8 @@ PHP_FUNCTION(mb_substr_count)
 		} else {
 			unsigned int num_errors = 0;
 			needle_u8 = mb_fast_convert((unsigned char*)ZSTR_VAL(needle), ZSTR_LEN(needle), enc, &mbfl_encoding_utf8, 0, MBFL_OUTPUTFILTER_ILLEGAL_MODE_BADUTF8, &num_errors);
-			if (!num_errors && !ZSTR_IS_INTERNED(needle)) {
-				GC_ADD_FLAGS(needle, IS_STR_VALID_UTF8);
+			if (!num_errors) {
+				mark_zstr_as_utf8(needle);
 			}
 		}
 	} else {
@@ -5567,8 +5589,8 @@ static bool mb_check_str_encoding(zend_string *str, const mbfl_encoding *encodin
 			return true;
 		}
 		bool result = mb_fast_check_utf8(str);
-		if (result && !ZSTR_IS_INTERNED(str)) {
-			GC_ADD_FLAGS(str, IS_STR_VALID_UTF8);
+		if (result) {
+			mark_zstr_as_utf8(str);
 		}
 		return result;
 	} else {

ext/opcache/zend_shared_alloc.c

@@ -628,7 +628,7 @@ const char *zend_accel_get_shared_model(void)
 	return g_shared_model;
 }
 
-void zend_accel_shared_protect(bool protected)
+ZEND_API void zend_accel_shared_protect(bool protected)
 {
 #ifdef HAVE_MPROTECT
 	int i;

ext/opcache/zend_shared_alloc.h

@@ -200,7 +200,7 @@ const char *zend_accel_get_shared_model(void);
  * @param protected true to protect shared memory (read-only), false
  * to unprotect shared memory (writable)
  */
-void zend_accel_shared_protect(bool protected);
+ZEND_API void zend_accel_shared_protect(bool protected);
 
 #ifdef USE_MMAP
 extern const zend_shared_memory_handlers zend_alloc_mmap_handlers;