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To: Nikita Popov <nikita.ppv@gmail.com>
Cc: internals@lists.php.net
Date: Sat, 14 Apr 2018 11:35:18 +0200
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Subject: Re: [PHP-DEV] Request-global hashtable initialization
From: HMWiesinger@liwjatan.at (Heinz Wiesinger)

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On Friday, 13 April 2018 08:16:24 CEST Heinz Wiesinger wrote:
> On Thursday, 12 April 2018 22:34:52 CEST Nikita Popov wrote:
> > On Thu, Apr 12, 2018 at 9:53 PM, Heinz Wiesinger <HMWiesinger@liwjatan.at>
> > 
> > wrote:
> > > Hi everyone!
> > > 
> > > I ventured into writing my first PHP extension and did pretty well so
> > > far
> > > following the existing documentation and example code inside the php
> > > source.
> > > 
> > > However, I hit an odd bug in my code that I can't quite explain. I'm
> > > obviously
> > > missing something and I hope someone here can point me in the right
> > > direction
> > > 
> > > :)
> > > 
> > > I'd like to set up a request global hashtable. For now I'm running
> > > ALLOC_HASHTABLE() and zend_hash_init() inside PHP_GINIT_FUNCTION. I then
> > > have
> > > a user function that's supposed to add entries to that hashtable and
> > > another
> > > user function that reads entries from the hashtable.
> > > 
> > > I tested with code passed directly on the command line (using php -r)
> > > and
> > > that
> > > works just like I would expect it too. The value gets written to the
> > > hashtable
> > > and I can read it afterwards from the other function. I also verified
> > > it's
> > > the
> > > same value that I first stored, so from what I can tell the basic
> > > functionality is good.
> > > 
> > > When I take the same testcode and write it into a file, and then run php
> > > on
> > > that file, execution aborts trying to allocate almost 2GB of memory when
> > > trying to store the value in the hashtable (using zend_hash_update()). I
> > > can
> > > see PHP_GINIT_FUNCTION being executed in that case as well so I'd assume
> > > the
> > > hashtable is setup just fine. Yet something is different.
> > > 
> > > What's the difference between " php -r '' " and "php test.php" in that
> > > regard?
> > > 
> > > I uploaded my current state of the extension to github in case someone
> > > would
> > > like to take a closer look at the code: https://github.com/pprkut/
> > > autoload-psr
> > > 
> > > Thanks in advance!
> > > 
> > > Grs,
> > > Heinz
> > 
> > https://github.com/pprkut/autoload-psr/blob/27cfc53c864116cf0b65b8f7e69464
> > e1 5b3fdef5/autoload_psr.c#L175 should be using ZVAL_STR_COPY. The
> > hashtable API does not automatically incref stored values.
> > 
> > I'd suggest running under USE_ZEND_ALLOC=0 valgrind to check for further
> > memory issues. Differences in the mode of execution are likely just
> > incidental.
> 
> Thanks for the pointers! I tried running it under valgrind, but couldn't
> find anything. So I tried without valgrind, but with USE_ZEND_ALLOC=0 and
> found that I can't reproduce the problem like that. Looks to me that
> something I do doesn't play well with the zend allocator.
> 
> Incidentally valgrind also doesn't tell me about the issue with ZVAL_STR
> that you pointed out. Maybe I'm using it wrong? I tried
> 
> USE_ZEND_ALLOC=0 valgrind --tool=memcheck --leak-check=full php -
> dextension=modules/autoload_psr.so test2.php

I moved the hashtable initialization out of PHP_GINIT_FUNCTION and do it on-
demand now in the respective user functions. That seems to have done the 
trick, as segfaults and oom messages are gone now.

Grs,
Heinz
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