Segfault in `execute_ex`: `EX(run_time_cache)` is NULL for a trait-copied `private static` method (no opcache, no JIT)
まだ誰も着手していません。
- 主要言語
- C
- スター
- 40.4k
- フォーク
- 8.1k
- 平均マージ
- 2日 13時間
- マージ済み PR(30日)
- 96
説明
Description
We are seeing a reproducible-in-aggregate segfault in the Zend VM on PHP 8.3.31
and 8.3.32 (Ubuntu 24.04, deb.sury.org builds, NTS). It occurs ~36 times/week on
one CI host under a Laravel application served by php -S (via
php artisan serve). Because the built-in server is a single process, each crash
takes the server down and every subsequent request is refused.
The engine executes an op_array whose run_time_cache is NULL, then performs a
run-time cache slot lookup against it.
Faulting instruction and registers, from a core dump (8.3.32):
=> execute_ex+15353: mov (%rdx,%rax,1),%rbx
rdx = 0x0 <- run-time cache base
rax = 0x8 <- cache slot offset
execute_ex+15357: test %rbx,%rbx
execute_ex+15360: je ...
Read directly from the core:
run_time_cache (execute_data + 0x40) = 0x0
Kernel log line (identical every time, same binary offset on every occurrence):
php8.3[3641252]: segfault at 8 ip ...2a3729 sp ... error 4 in php8.3[...+32f000]
error 4 = user-mode read of a non-present page; the faulting address is
literally 0 + 8, i.e. slot 1 of a NULL cache.
The function involved
Frame 0 is always the same PHP function, reached from different callers. Walking
execute_data out of the core (%r14; func at +0x18, prev_execute_data at
+0x30, function_name at +0x08, zend_string.val at +0x18):
#0 resolveTenantId <- always frame 0
#1 {closure} (an Eloquent global scope closure)
#2 {closure} -> callScope -> applyScopes
core A: ... -> get -> first -> resolveRouteBinding -> substituteImplicitBindings
core B: ... -> toBase -> __call -> currentAgencyHasStudio -> {closure}
resolveTenantId() is a private static method defined in a trait, and that
trait is used by ~68 classes — so the method exists as ~68 separate op_arrays,
each with its own ZEND_MAP_PTR run-time cache. It is called on a very hot path
(every scoped query). Its body is small:
private static function resolveTenantId(): int|string|null
{
if (! function_exists('app')) {
return null;
}
$resolver = app()->bound(TenantResolver::class)
? app(TenantResolver::class)
: null;
return $resolver?->currentTenantId();
}
Ruled out
- opcache / JIT —
opcache.enable_cli => Off. opcache.so is loaded as a
module but caches nothing in this SAPI; JIT therefore never engages. (This
distinguishes it from #22158, which is JIT-specific, and #9396, which requires
opcache.) PHP_CLI_SERVER_WORKERS— unset; confirmed absent from the core's
environment, so the experimental forking server is not involved.- pcov / xdebug or any other VM-hooking extension — not among the 65
extensions loaded in the crashed process. - Userland recursion into the same scope — the class queried by the resolver
is exempt from the global scope, so there is no re-entry loop. - PHP 8.3.33 — its NEWS contains only Date/GD/PGSQL/Phar entries; nothing
engine-related, so we do not expect it to change this.
Environment
- PHP 8.3.32 (
8.3.32-1+ubuntu24.04.1+deb.sury.org+1) and 8.3.31, both NTS, both
affected, on two separate hosts - Ubuntu 24.04
- SAPI:
cli-server(php -S) - opcache loaded,
opcache.enable_cli=Off, JIT inactive - 65 extensions loaded
What I have and what I don't
I have core dumps and can extract any additional structure from them on request
(op_array fields, the zend_function at execute_data+0x18, the opline, etc.).
I do not have a minimal reproducer, and I have tried. The crash is frequent
in aggregate (~5/day) but not deterministic per-request, which is consistent with
an allocation- or lifetime-related issue around the run-time cache rather than a
specific input.
Attempts, both run on the same affected binary and host, both negative:
- Structural mimic — one trait with a
private staticmethod calling
function_exists(), a container-ish helper and a nullsafe method call; 68
classes using the trait; each invoked through astatic functionclosure via
call_user_func(to mirror the global-scope indirection); served by
php -S. 400 requests, ~186k calls: no crash. - Same, scaled to 1500 trait-using classes + 1500 free functions to force
ZEND_MAP_PTRtable growth and reallocation across a long-lived
php -Sprocess. 500 requests: no crash.
So the trait-copy structure alone is not sufficient. Something else in the real
workload is required — plausibly overall arena/memory pressure, the volume of
classes autoloaded per request, or live PDO/session activity. I mention the
negative results explicitly so nobody re-runs the same experiment.
I have the core dumps and can extract any additional structure from them on
request, or run a diagnostic/assertion build against the live workload — that is
likely the fastest route to a fix, since the workload reproduces it reliably in
aggregate even though a reduced case does not.
コントリビューションガイド
はじめの一歩
- issue を最後まで読み、次にプロジェクトのコントリビューションガイドを読みます。
- 着手することを issue にコメントします — 二人が同じ作業をするのを防げます。
- リポジトリをフォークし、ブランチを切って変更します。
- issue 番号を参照したプルリクエストを送ります。
調査の方向性
execute_ex の障害から調査を開始し、コアダンプに記載されている execute_data、op_array、および NULL run_time_cache を調べてください。影響を受ける php -S ワークロードに対して診断ビルドまたはアサーションビルドを使用し、trait からコピーされた private static メソッドのランタイムキャッシュの状態を呼び出しごとに比較してください。無効なキャッシュアクセスを再現し、エンジンレベルで確認済みの原因と、回帰テストまたは修正を特定できれば完了です。
索引モデルが issue の本文から書いたものです。
評価
- 技術スタック
- c, php
- 領域
- backend, compilers
- issue の種類
- バグ
- 難易度
- 5/5
- 見積もり時間
- 1週間以上
- 活発さ
- 静か
- 明瞭さ
- 説明が足りない
- 初心者へのやさしさ
- 25/100