Edit report at https://bugs.php.net/bug.php?id=74804&edit=1
ID: 74804
User updated by: steve dot hall+bugs dot php dot net at rg456 dot co
dot uk
Reported by: steve dot hall+bugs dot php dot net at rg456 dot co
dot uk
Summary: Segfault when instantiating object in array
Status: Open
Type: Bug
Package: Reproducible crash
Operating System: Alpine 3.4 & Windows 10
PHP Version: 7.1.6
Block user comment: N
Private report: N
New Comment:
Thank you for your time on this nikic, it is much appreciated.
Here is a valgrind from php -nhttps://gist.github.com/sh41/30890b1021cac6bec0530292ffc5fd11
I've included the output of php -n -i so that you can see what extensions are
loaded. I think that openssl is compiled in, and it's also required by the program I'm
running, so don't think I can usefully revert to a version without it.
Must admit that I'm out of my depth when it comes to php internals, but if it helps, the times
I was able to catch the seg fault in action it seemed to happen at this line: https://github.com/symfony/symfony/blob/v3.3.2/src/Symfony/Component/VarDumper/Cloner/VarCloner.php#L123
Not sure if that helps to point in the right direction or not.
Is there anything else I can do to provide more information on this?
Previous Comments:
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[2017-06-23 14:31:43] nikic@php.net
The last valgrind output looks pretty good. This seems to be some kind of GC issue involving
destructors and nested GCs. From the valgrind output, what seems to be happening:
1. During the outer GC, while running a destructor and object is created.
2. During the inner GC that object is freed.
3. During the outer GC, there is an attempt to free the object again.
Not sure how we could actually end up in that situation though. It might help to find out which
__destruct() method is involved here. (From the trace, the __destruct() might be calling __invoke()
on a closure, though it's not clear if that's a direct call.)
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[2017-06-23 13:55:50] steve dot hall+bugs dot php dot net at rg456 dot co dot uk
New valgrind here with "export USE_ZEND_ALLOC=0" and ZEND_DONT_UNLOAD_MODULES=1 and a
couple of Invalid reads/writes:
https://gist.github.com/sh41/2dd25967ec598f4f48bbdf049df2e462#file-valgrind-L7126
I will try to eliminate un-needed extensions with -n and provide another one as soon as I can.
------------------------------------------------------------------------
[2017-06-23 11:20:43] nikic@php.net
It's okay if you don't get a segfault, the important part is whether you get invalid
reads/writes in valgrind. I would suggest to:
* Try running under php -n and only enable those extensions that are necessary to reproduce this.
In particular running with openssl adds a lot of noise to valgrind output, because openssl
developers have some very peculiar views on reading uninitialized data from memory.
* Try setting ZEND_DONT_UNLOAD_MODULES=1 to avoid some of the ???s in the output.
* Try running with USE_ZEND_ALLOC=0 again and see if there are still invalid read/writes, even if
there is no segfault. (Disregard the ones caused by "invalid file descriptor", those
don't seem related.)
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[2017-06-23 10:49:21] steve dot hall+bugs dot php dot net at rg456 dot co dot uk
With
export USE_ZEND_ALLOC=0
I cannot cause the segfault in valgrind, but as soon as I do
export USE_ZEND_ALLOC=1
The segfault reappears.
New file here:
https://gist.github.com/sh41/df3d2b8e3695d67ef59653b83e5604d0
------------------------------------------------------------------------
[2017-06-23 10:39:52] steve dot hall+bugs dot php dot net at rg456 dot co dot uk
Apologies, I spoke to soon. The segfault is happening again. I am attempting to capture a new
valgrind without the igbinary extension, but the segfault goes away when I'm running in
valgrind.
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