Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:57826
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Received-SPF: pass (pb1.pair.com: domain zend.com designates 212.199.177.89 as permitted sender)
To: Gwynne Raskind <gwynne@darkrainfall.org>
Date: Mon, 13 Feb 2012 11:57:31 +0200
User-Agent: KMail/1.13.7 (Linux/2.6.37; KDE/4.7.2; i686; ; )
CC: Stas Malyshev <smalyshev@sugarcrm.com>, Dmitry Stogov <dmitry@zend.com>,
	PHP Internals <internals@lists.php.net>, Alex Haiut <alex.h@zend.com>, Zeev
 Suraski <zeev@zend.com>, Eran Ifrah <eran@zend.com>, Lior Kaplan
	<lior.k@zend.com>
References: <201202121409.54891.yoram.b@zend.com> <201202131138.00917.yoram.b@zend.com> <CAMWw8k-8STTydwcA_p+mJ5J4rJCHmAqhG1r96U3SLL-u0pQk6Q@mail.gmail.com>
In-Reply-To: <CAMWw8k-8STTydwcA_p+mJ5J4rJCHmAqhG1r96U3SLL-u0pQk6Q@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit
Message-ID: <201202131157.31848.yoram.b@zend.com>
Subject: Re: [PHP-DEV] Re: restore user opcode handler in PHP
From: yoram.b@zend.com (yoram bar haim)

Indeed, when using dlsym the value is recreated.
now the question is what happens at apache restart (on mac) that causes 
incorrect behavior.
a-priory to that question, static initializers can not be trusted on some 
situations.

On Monday, February 13, 2012 11:44:15 AM Gwynne Raskind wrote:
> On Mon, Feb 13, 2012 at 04:38, yoram bar haim <yoram.b@zend.com> wrote:
> > Here is a simple test program that reproduce the issue on mac:
> [snip]
> 
> > shell> gcc -o lib.so -shared lib.c
> > shell> gcc -o main main.c lib.so
> > shell> ./main
> 
> This example is flawed.
> 
> The manpage for dlclose(3) on Darwin explicitly states that a library
> linked by the executable will never be unloaded. You link directly to
> the library here. Also, you use prototypes of the library's functions
> rather than calling dlsym(3), forcing you to link to the library,
> defeating the entire point of loading it with dlopen(3) in the first
> place. I've included a test which does not show the issue at the
> bottom of this message.
> 
> (As a side note of interest, OS X has historically always had issues
> with unloading images from the address space; for example, even in
> Lion, if you unload an image containing Objective-C symbols, you stand
> a pretty good chance of crashing. Image unloading simply didn't exist
> at all in any useful form before Leopard.)
> 
> -- Gwynne Raskind
> 
> /* dylib.c - clang dylib.c -o dylib.dylib -dynamiclib */
> static int      var = 0;
> extern int getVar(void);
> extern void setVar(int value);
> int     getVar(void) { return var; }
> void    setVar(int value) { var = value; }
> 
> /* loader.c - clang loader.c -o loader */
> #include <stdio.h>
> #include <dlfcn.h>
> int    main(int argc, char **argv)
> {
>         void    *libh = dlopen("dylib.dylib", 0);
>         int     (*getfunc)() = dlsym(libh, "getVar");
>         void    (*setfunc)(int) = dlsym(libh, "setVar");
> 
>         printf("First load value: %d\n", getfunc());
>         setfunc(5);
>         printf("First load set value: %d\n", getfunc());
>         dlclose(libh);
>         libh = dlopen("dylib.dylib", 0);
>         getfunc = dlsym(libh, "getVar");
>         setfunc = dlsym(libh, "setVar");
>         printf("Second load value: %d\n", getfunc());
>         return 0;
> }
> 
> /* output */
> $ uname -v ; clang --version ; ./loader
> Darwin Kernel Version 11.3.0: Thu Jan 12 18:47:41 PST 2012;
> root:xnu-1699.24.23~1/RELEASE_X86_64
> clang version 3.0 (tags/RELEASE_30/final)
> First load value: 0
> First load set value: 5
> Second load value: 0