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To: Derick Rethans <derick@derickrethans.nl>,
 PHP Developers Mailing List <internals@lists.php.net>
References: <alpine.DEB.2.20.1611091403200.5688@whisky.home.derickrethans.nl>
Cc: Dmitry Stogov <dmitry@zend.com>, Nikita Popov <nikita.ppv@gmail.com>
Message-ID: <cfcea58d-9a5b-5649-be4c-5181d33cad78@gmx.de>
Date: Wed, 9 Nov 2016 15:48:03 +0100
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Subject: Re: PHP 5.6 static access valgrind issue
From: cmbecker69@gmx.de ("Christoph M. Becker")

Hi Derick!

On 09.11.2016 at 15:21, Derick Rethans wrote:

> Hi!
> 
> Through https://bugs.xdebug.org/view.php?id=1185 I ran into a bug in PHP 
> proper. Apparently, this script:
> 
> 	<?php
> 
> 	class A {
> 		static private $a;
> 
> 		static public function init() {
> 			self::$a = 123;
> 		}
> 	}
> 
> 	A::init();
> 
> 	echo 'succcess!';
> 
> And running it with "valgrind php -n index.php", produces:
> 
> 	root@debian-8-64bit:/home/derick/xdebug-issue-1185# valgrind php -n index.php
> 	==760== Memcheck, a memory error detector
> 	==760== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
> 	==760== Using Valgrind-3.10.0 and LibVEX; rerun with -h for copyright info
> 	==760== Command: php -n index.php
> 	==760== 
> 	==760== Conditional jump or move depends on uninitialised value(s)
> 	==760==    at 0x797992: zend_std_get_static_method (zend_object_handlers.c:1261)
> 	==760==    by 0x7B66FE: ZEND_INIT_STATIC_METHOD_CALL_SPEC_CONST_CONST_HANDLER (zend_vm_execute.h:3887)
> 	==760==    by 0x7A379F: execute_ex (zend_vm_execute.h:363)
> 	==760==    by 0x76E2AF: zend_execute_scripts (zend.c:1341)
> 	==760==    by 0x70CC87: php_execute_script (main.c:2613)
> 	==760==    by 0x81A990: do_cli (php_cli.c:998)
> 	==760==    by 0x431996: main (php_cli.c:1382)
> 	==760== 
> 	succcess!==760== 
> 	==760== HEAP SUMMARY:
> 	==760==     in use at exit: 96 bytes in 3 blocks
> 	==760==   total heap usage: 19,605 allocs, 19,602 frees, 3,589,979 bytes allocated
> 	==760== 
> 	==760== LEAK SUMMARY:
> 	==760==    definitely lost: 0 bytes in 0 blocks
> 	==760==    indirectly lost: 0 bytes in 0 blocks
> 	==760==      possibly lost: 0 bytes in 0 blocks
> 	==760==    still reachable: 96 bytes in 3 blocks
> 	==760==         suppressed: 0 bytes in 0 blocks
> 	==760== Rerun with --leak-check=full to see details of leaked memory
> 	==760== 
> 	==760== For counts of detected and suppressed errors, rerun with: -v
> 	==760== Use --track-origins=yes to see where uninitialised values come from
> 	==760== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
> 
> This is with the latest PHP-5.6 branch, and the GCC that comes with 
> Debian Jessie:
> 
> 	root@debian-8-64bit:/home/derick/xdebug-issue-1185# gcc --version
> 	gcc (Debian 4.9.2-10) 4.9.2
> 
> 
> Annoyingly, I can only produce this on a Debian Jessie (8.6) fresh install, and
> not on my local machine. I can't seem to find the problem either, but I *can*
> provide a VM and instructions to reproduce this. Or provide SSH access 
> into it upon request.
> 
> Anybody wants to try and fix this? I'm going to see whether PHP 7.0 and 
> 7.1 have a similar issue too.

zend_std_get_static_method() declares use_heap[1] (if there's support
for alloca), but doesn't initialize it with SET_ALLOCA_FLAG()[2].  It
seems to me that ALLOCA_FLAG()[3] should be defined like so:

  # define ALLOCA_FLAG(name) \
    zend_bool name = 0;

[1] <http://lxr.php.net/xref/PHP-5.6/Zend/zend_object_handlers.c#1184>
[2] <http://lxr.php.net/source/xref/PHP-5.6/Zend/zend.h#200>
[3] <http://lxr.php.net/source/xref/PHP-5.6/Zend/zend.h#198>

-- 
Christoph M. Becker