php / php/php-src

JIT segmentation fault in PHP 8.1

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Bug Category: JIT
Dominant language
C
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Avg merge
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Description

Description

PHP 8.1.0 + 8.1.1 produces segfault, randomly. Downgrading to 8.0 solves the issue.

--core dump---

BFD: Warning: coredump-php-fpm.30267 is truncated: expected core file size >= 5413076992, found: 35983360.
[New LWP 30267]
[New LWP 1887]
[New LWP 1886]
[New LWP 1888]
Cannot access memory at address 0x7f277dbb3128
Cannot access memory at address 0x7f277dbb3120
Failed to read a valid object file image from memory.
Core was generated by `php-fpm: pool xxxxxx '.

Program terminated with signal 11, Segmentation fault.
#0 0x000055bbf04c0f25 in ZEND_NEW_SPEC_CONST_UNUSED_HANDLER () at /usr/src/debug/php-8.1.1/Zend/zend_vm_execute.h:10137
10137 ce = CACHED_PTR(opline->op2.num);
(gdb) bt
Python Exception <class 'gdb.MemoryError'> Cannot access memory at address 0x7ffdc940e3a8:
(gdb) bt
#0 0x000055bbf04c0f25 in ZEND_NEW_SPEC_CONST_UNUSED_HANDLER () at /usr/src/debug/php-8.1.1/Zend/zend_vm_execute.h:10137
Cannot access memory at address 0x7ffdc940e3a8
(gdb) frame 0
#0 0x000055bbf04c0f25 in ZEND_NEW_SPEC_CONST_UNUSED_HANDLER () at /usr/src/debug/php-8.1.1/Zend/zend_vm_execute.h:10137
10137 ce = CACHED_PTR(opline->op2.num);
(gdb) info frame
Stack level 0, frame at 0x7ffdc940e3b0:
rip = 0x55bbf04c0f25 in ZEND_NEW_SPEC_CONST_UNUSED_HANDLER (/usr/src/debug/php-8.1.1/Zend/zend_vm_execute.h:10137); saved rip Cannot access memory at address 0x7ffdc940e3a8

this is the only available info in the core dump.

PHP Version

PHP 8.1.0 + 8.1.1

Operating System

CentOS 7

Contributor guide

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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

Begin with the core-dump trace at Zend/zend_vm_execute.h:10137, specifically ZEND_NEW_SPEC_CONST_UNUSED_HANDLER, and compare the PHP 8.1.0 and 8.1.1 JIT behavior against PHP 8.0. The report provides no reproducer beyond an intermittent php-fpm crash, so done requires isolating a reproducible failure and verifying the fix against it.

Written by the indexing model from the issue text.

Assessment

Tech stack
c, php
Domain
compilers
Issue type
Bug
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
20/100

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