Edit report at https://bugs.php.net/bug.php?id=72286&edit=1
ID: 72286
Comment by: php at mattlight dot biz
Reported by: php at mattlight dot biz
Summary: Segmentation fault (segfault) During Garbage
Collection
Status: Open
Type: Bug
Package: Reproducible crash
Operating System: CentOS Linux release 7.2.1511
PHP Version: 5.6.22
Block user comment: N
Private report: N
New Comment:
In case it might be useful, here is the gdb output:
(gdb) bt
#0 0x00007f5966ac5e98 in zend_std_object_get_class ()
#1 0x00007f5966ac5ec5 in zend_std_get_debug_info ()
#2 0x00007f5966a16e83 in php_var_dump ()
#3 0x00007f5966a1730a in zif_var_dump ()
#4 0x00007f5966a8ce1b in dtrace_execute_internal ()
#5 0x00007f5966b468e4 in zend_do_fcall_common_helper_SPEC ()
#6 0x00007f5966adac28 in execute_ex ()
#7 0x00007f5966a8ccf9 in dtrace_execute_ex ()
#8 0x00007f5966a8eaf3 in zend_call_function ()
#9 0x00007f5966ab6838 in zend_call_method ()
#10 0x00007f5966ac5929 in zend_objects_destroy_object ()
#11 0x00007f5966abf04a in gc_collect_cycles ()
#12 0x00007f5966aaf889 in zif_gc_collect_cycles ()
#13 0x00007f5966a8ce1b in dtrace_execute_internal ()
#14 0x00007f5966b468e4 in zend_do_fcall_common_helper_SPEC ()
#15 0x00007f5966adac28 in execute_ex ()
#16 0x00007f5966a8ccf9 in dtrace_execute_ex ()
#17 0x00007f5966a9fa6b in zend_execute_scripts ()
#18 0x00007f5966a3aea2 in php_execute_script ()
#19 0x00007f5966b487e8 in do_cli ()
#20 0x00007f5966918f6a in main ()
Previous Comments:
------------------------------------------------------------------------
[2016-05-30 02:49:14] php at mattlight dot biz
Description:
------------
A segmentation fault occurs during garbage collection when the following criteria are all met:
- Object "A" stores a reference to itself in an instance variable
- Object "A" also stores another object, Object "B" in another instance
variable (instance of stdClass is fine)
- The destructor of object "A" attempts to reference object "B" only after
check that object "B" is still set
- Object "A" is instantiated from some other object
The issue affects PHP 5.6 and 5.5 (and 5.4), but not 7.0. I have set the test case up in Travis CI:
https://travis-ci.org/lightster/php-circular-reference-segfault
The scenario I presented is a simplified scenario of an issue I encountered when using phpamqplib.
Other people have reported this issue to phpamqplib but since the library is written purely in PHP
it cannot be responsible for preventing a segmentation fault: https://github.com/php-amqplib/php-amqplib/issues/261
My bug report might be the same issue that was reported in https://bugs.php.net/bug.php?id=71958 but I was
unable to confirm one way or another.
Test script:
---------------
https://raw.githubusercontent.com/lightster/php-circular-reference-segfault/master/segfault.php
Expected result:
----------------
I would expect either "the object exists" or "will not get here" to be output. I
know the order that destructors is called is documented to be undefined, so either output is
probably acceptable.
Actual result:
--------------
PHP exits with a segmentation fault:
Array
(
[0] => Core
[1] => date
[2] => ereg
[3] => libxml
[4] => openssl
[5] => pcre
[6] => zlib
[7] => filter
[8] => hash
[9] => pcntl
[10] => readline
[11] => Reflection
[12] => SPL
[13] => session
[14] => standard
[15] => mhash
)
string(24) "we are about to segfault"
string(15) "segfaults here:"
Segmentation fault (core dumped)
------------------------------------------------------------------------
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Edit this bug report at https://bugs.php.net/bug.php?id=72286&edit=1