Segmentation fault in FFI

[YuanchengJiang]

Description

The following code:

<?php
require_once('utils.inc');
$zend = FFI::cdef("
typedef size_t (*zend_write_func_t)(const char *str, size_t str_length);
extern zend_write_func_t zend_write;
", ffi_get_php_dll_name());
$zend->zend_write = $fusion;
echo "Hello World!\n";

Resulted in this output:

AddressSanitizer:DEADLYSIGNAL
=================================================================
==2090797==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x000000000000 bp 0x7ffc0ff57fc0 sp 0x7ffc0ff57ea8 T0)
==2090797==Hint: pc points to the zero page.
==2090797==The signal is caused by a READ memory access.
==2090797==Hint: address points to the zero page.
    #0 0x0  (<unknown module>)
    #1 0x557a64243713 in execute_ex /php-src/Zend/zend_vm_execute.h:58565:7
    #2 0x557a64245872 in zend_execute /php-src/Zend/zend_vm_execute.h:64217:2
    #3 0x557a64f45b01 in zend_execute_script /php-src/Zend/zend.c:1928:3
    #4 0x557a63856798 in php_execute_script_ex /php-src/main/main.c:2574:13
    #5 0x557a63857858 in php_execute_script /php-src/main/main.c:2614:9
    #6 0x557a64f59276 in do_cli /php-src/sapi/cli/php_cli.c:935:5
    #7 0x557a64f53944 in main /php-src/sapi/cli/php_cli.c:1310:18
    #8 0x7f16ef89dd8f  (/lib/x86_64-linux-gnu/libc.so.6+0x29d8f) (BuildId: 490fef8403240c91833978d494d39e537409b92e)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV (<unknown module>) 
==2090797==ABORTING

PHP Version

PHP 8.4.0-dev

Operating System

ubuntu 22.04

[cmb69]

I can reproduce the segfault, but this doesn't look like a bug. After all, overwriting zend_write with NULL, and then calling it obviously causes issues. Same for other internal function pointers.