fix: refuse to start on a ZTS build with Zend signals

[nicolas-grekas]

PHP enables Zend signals by default, docs/compile.md and the Dockerfiles pass --disable-zend-signals, and nothing checks it. Building PHP by hand without that flag gives a server that never finishes booting, with memory growing by hundreds of megabytes per second until the process is killed. No error, no log line, and the stacks only show PHP copying hash tables, so it reads like a slow machine.

What happens: FrankenPHP has its own SAPI and never calls zend_signal_startup(), which the cli and embed SAPIs of php-src do, so zend_signal_globals_id stays 0. When zend_register_standard_ini_entries() reaches zend.signal_check, OnUpdateBool resolves its address as ts_resource(*(int *)mh_arg2) + mh_arg1; ts_resource(0) returns the tsrm_tls_entry of the calling thread itself, so the bool write lands 16 bytes into it, on the thread_id field, and zeroes its low byte. TSRM never matches that thread again: ts_resource_ex() appends a new resource set and tail-recurses on every call, each level running executor_globals_ctor() and copying the constant, function and class tables. Watchpoint on the field, and the chain measured at 4013 entries before the process was killed.

This checks the flag PHP already reports through frankenphp_get_config() and fails Init() with an actionable error. Against a PHP built without the flag the tests now stop in 0.00s with that message instead of hanging; against a correctly built PHP the suite is unchanged.

Non-ZTS builds keep working: their ini entries address the globals directly, TSRM is not involved, so the check is limited to ZTS.

The alternative would be to call zend_signal_startup() like the embed SAPI does. That is not enough: with Zend signals actually running, PHP's handlers and the Go runtime's fight over the same signals and the test suite crashes, which is presumably why the flag is documented in the first place.

[withinboredom]

Nice find!

[dunglas]

I wonder if calling it conditionally
would fix the issue.

[dunglas]

Thanks!