ext/opcache: Mark dl()-created persistent strings as thread-local

[iliaal]

Fixes the nightly LINUX_X64_VARIATION_DEBUG_ZTS failures of frameless_temporary_opcache.phpt and, on 8.5+, frameless_temporary.phpt. Names that dl() registers during a request come back from opcache's interned-string handlers as plain persistent strings, so the first refcount change on one trips the ZEND_RC_DEBUG assertion. They belong to the request's temporary module, so they are now marked GC_PERSISTENT_LOCAL while zend_rc_debug is off, as during dl(); release builds are unaffected.

[Girgias]

I think this is correct, but I always get confused about marking request strings as persistent, so if @arnaud-lb could double check that would be great.

[arnaud-lb]

ZEND_RC_DEBUG forbids modifications of persistent strings during a request, because usually such strings can be accessed by other requests. GC_PERSISTENT_LOCAL signals that the string is actually not shared with other requests, so it's safe to modify.

@iliaal I think that doing it in accel_init_interned_string_for_php() weakens ZEND_RC_DEBUG because really we don't know if the string will be shared later.

There are a few dl()-only ZEND_RC_DEBUG workarounds already, I think that we should do that here again. dl() unsets zend_rc_debug, so we should add the flag only when zend_rc_debug is false, with a comment like

php-src/Zend/zend_string.c

Lines 315 to 316 in 8844427

	/* PHP shouldn't create persistent interned string during request,
	* but at least dl() may do this */

[iliaal]

Good point, thanks, a little bit ugly of a work-around but it makes sense especially given other use-cases

[arnaud-lb]

Looks good to me!