php / php/php-src

Zend GC assertion failure in gc_check_possible_root_no_ref with lazy proxy

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#20,861 3 comments 0 reactions 0 assignees View on GitHub

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Bug Category: Engine Status: Verified
Dominant language
C
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Avg merge
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Merged PRs (30d)
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Description

Description

The following code:

<?php
class A {
    public $_;
    public function __get($n) {
        global $obj;
        $obj->f =& $this->b;
        static $a = $a;
        foreach (get_defined_vars() as $k => $v) {}
        foreach (get_defined_vars() as $k => $v) {}
    }
}
class B extends A {}
$rc = new ReflectionClass(B::class);
$obj = $rc->newLazyProxy(fn() => new A);
$rc->initializeLazyObject($obj)->p;

Resulted in this output:

php: /path/to/php-src/Zend/zend_gc.h:105: gc_check_possible_root_no_ref: Assertion `(ref)->gc.u.type_info != (10 | ((1<<4) << 0))' failed.
Aborted
Commit
643cf6253e5
Configurations
CC="clang" CXX="clang++" CFLAGS="-fsanitize=address -g -O0" CXXFLAGS="-fsanitize=address -g -O0" ./configure --enable-debug --enable-address-sanitizer --disable-shared --with-pic
PHP Version
PHP 8.6.0-dev (cli) (built: Jan  8 2026 01:22:30) (NTS DEBUG)
Copyright (c) The PHP Group
Zend Engine v4.6.0-dev, Copyright (c) Zend Technologies
    with Zend OPcache v8.6.0-dev, Copyright (c), by Zend Technologies
Operating System

Ubuntu 22.04

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Reproduce the failure using the PHP snippet and the listed debug AddressSanitizer configuration, then start at Zend/zend_gc.h:105 and trace the lazy-proxy path involved in the assertion. Done means the reproducer no longer aborts with the Zend GC assertion; no specific test file is named in the issue.

Written by the indexing model from the issue text.

Assessment

Tech stack
c, php
Domain
backend
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
38/100

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