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

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.

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

Start at the execute_ex fault and inspect execute_data, the op_array, and the NULL run_time_cache described in the core dumps. Use a diagnostic or assertion build against the affected php -S workload, and compare the trait-copied private static method's runtime-cache state across calls. Done means reproducing the invalid cache access and identifying a confirmed engine-level cause and regression test or fix.

Written by the indexing model from the issue text.

Assessment

Tech stack
c, php
Domain
backend, compilers
Issue type
Bug
Difficulty
5/5
Estimated time
Over a week
Activity status
Quiet
Clarity
Needs clarification
Newbie friendliness
25/100

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