Assertion failure in Zend/zend_builtin_functions.c:1893

[YuanchengJiang]

Description

The following code:

<?php
$test = new _ZendTestFiber(function (): void {
$fiber->start();
});
var_dump($test->start());

Resulted in this output:

/php-src/Zend/zend_builtin_functions.c:1893: void zend_fetch_debug_backtrace(zval *, int, int, int): Assertion `call->func' failed.
Aborted (core dumped)

Not sure if it can be triggered in other ways without testclass.

PHP Version

PHP 8.4.0-dev

Operating System

ubuntu 22.04

[ndossche]

That assertion was added in #15952, but the assert just seems to ignore the existance of fibers afaict

[ndossche]

Test can be simplified to:

$test = new _ZendTestFiber(function (): void {
    print_r(debug_backtrace());
});
$test->start();

I cannot trigger this with Fiber, only with the internal test class... Would need to think more about this.
Removing the assert works fine, but I'm not so sure that's the right thing to do.

[iluuu1994]

It seems _ZendTestFiber installs an empty frame, for some reason:

php-src/ext/zend_test/fiber.c

Lines 91 to 95 in 6c5749f

	execute_data = (zend_execute_data *) stack->top;
	memset(execute_data, 0, sizeof(zend_execute_data));
	EG(current_execute_data) = execute_data;

Apparently, this is ok for the top function, as it exists the loop:

php-src/Zend/zend_builtin_functions.c

Lines 1898 to 1902 in 6c5749f

	if (!prev) {
	/* add frame for a handler call without {main} code */
	if (EXPECTED((ZEND_CALL_INFO(call) & ZEND_CALL_TOP_FUNCTION) == 0)) {
	break;
	}

I don't know if there are any extensions that do this, but it seems like they would have already reported the issue if so. So maybe let's just set it to a dummy function?

diff --git a/ext/zend_test/fiber.c b/ext/zend_test/fiber.c
index 30dbfa06e5..4518c26c6f 100644
--- a/ext/zend_test/fiber.c
+++ b/ext/zend_test/fiber.c
@@ -91,6 +91,7 @@ static ZEND_STACK_ALIGNED void zend_test_fiber_execute(zend_fiber_transfer *tran
 		execute_data = (zend_execute_data *) stack->top;
 
 		memset(execute_data, 0, sizeof(zend_execute_data));
+		execute_data->func = (zend_function *) &zend_pass_function;
 
 		EG(current_execute_data) = execute_data;
 		EG(jit_trace_num) = 0;

We can also remove the assert, if you think that's preferable.

[ndossche]

@iluuu1994 Your patch suggestion makes sense to me.