opcache: set ZEND_ACC_PRELOADED for compile-only preloaded enums

[Nibbler999]

Disclosure: this description, the patch and its test were drafted with an LLM.

Summary

GH-17835 fixed GH-17715 for enums that preload declares. It does not cover enums that preload only compiles, and those still crash on 8.4 and 8.5.

// preload.php
opcache_compile_file(__DIR__ . '/e.php');

// e.php
enum E { case Foo; }

// request
E::cases();   // SIGSEGV with any Observer API extension loaded

Cause

zend_enum_register_func() sets ZEND_ACC_PRELOADED inside the if (EG(active)) branch. zend_persist_class_method() keys on that flag to choose ZEND_MAP_PTR_NEW_STATIC() over ZEND_MAP_PTR_NEW(), i.e. a run_time_cache slot that survives into every request — which is what a class living in SHM permanently needs.

An enum that preload reaches via opcache_compile_file() is not linked while the preload script executes. It is linked from preload_link(), which runs after the preload request has ended, so EG(active) is already false, the else branch is taken and the flag is never set.

gdb on the crash, on an unpatched 8.5.9:

Program received signal SIGSEGV, Segmentation fault.
#0  zend_observer_fcall_begin_specialized (...) at Zend/zend_observer.h:92
#1  ZEND_DO_FCALL_SPEC_OBSERVER_HANDLER ()   at Zend/zend_vm_execute.h:2281
#2  execute_ex (...)                         at Zend/zend_vm_execute.h:116541

function : cases        type: 1 (internal)     T: 1
fn_flags : 0x2002011  = PUBLIC|STATIC|HAS_RETURN_TYPE|ARENA_ALLOCATED
                        ZEND_ACC_PRELOADED (1<<10) absent
run_time_cache : 0

ZEND_OBSERVER_DATA() computes RUN_TIME_CACHE(...) + handle = NULL + 0 and dereferences it — the same null deref, and the same Zend/zend_observer.h:92, that GH-17715's UBSAN output reports.

Fix

Move the tag out of the EG(active) branch so both linking paths set it. The compile-only case then follows the identical, already-proven route as the declared case; no new mechanism is introduced.

Test

ext/opcache/tests/preload_enum_observed_compile_only.phpt mirrors the existing preload_enum_observed.phpt and reuses its preload_enum.inc fixture, changing only how preload reaches it.