php / php/php-src

Segfault in `execute_ex`: `EX(run_time_cache)` is NULL for a trait-copied `private static` method (no opcache, no JIT)

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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 / JITopcache.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:

  1. Structural mimic — one trait with a private static method calling
    function_exists(), a container-ish helper and a nullsafe method call; 68
    classes using the trait; each invoked through a static function closure via
    call_user_func (to mirror the global-scope indirection); served by
    php -S. 400 requests, ~186k calls: no crash.
  2. Same, scaled to 1500 trait-using classes + 1500 free functions to force
    ZEND_MAP_PTR table growth and reallocation across a long-lived
    php -S process. 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.

Beitragsleitfaden

Beitragsleitfaden öffnen

Erste Schritte

  1. Lies das ganze Issue und danach den Beitragsleitfaden des Projekts.
  2. Schreib ins Issue, dass du es übernimmst — das erspart doppelte Arbeit.
  3. Forke das Repository und arbeite in einem Branch.
  4. Öffne einen Pull Request, der die Issue-Nummer nennt.

Rechercherichtung

Beginne beim execute_ex-Fehler und untersuche den in den Core-Dumps beschriebenen execute_data, das op_array und den NULL run_time_cache. Verwende einen Diagnose- oder Assertion-Build für die betroffene php -S-Workload und vergleiche den Runtime-Cache-Zustand der durch ein Trait kopierten privaten statischen Methode über mehrere Aufrufe hinweg. Als erledigt gilt die Reproduktion des ungültigen Cache-Zugriffs und die Identifizierung einer bestätigten Ursache auf Engine-Ebene sowie eines Regressionstests oder Fixes.

Vom Indexierungsmodell aus dem Issue-Text verfasst.

Bewertung

Tech-Stack
c, php
Bereich
backend, compilers
Issue-Typ
Bug
Schwierigkeit
5/5
Geschätzter Aufwand
Über eine Woche
Aktivitätsstatus
Ruhig
Klarheit
Muss geklärt werden
Anfängerfreundlichkeit
25/100

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