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To: Mark Skilbeck <markskilbeck@gmail.com>
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Date: Sun, 1 Nov 2009 21:21:14 +0000
Cc: "internals@lists.php.net" <internals@lists.php.net>
Subject: Re: [PHP-DEV] Seg fault when using active_symbol_table called from userspace function.
From: scott@macvicar.net (Scott MacVicar)

On 1 Nov 2009, at 21:09, Mark Skilbeck <markskilbeck@gmail.com> wrote:

> Can you explain to me why the following causes a segfault:
>
> [code]
> PHP_FUNCTION(sample_var_a_exists)
> {
>    if (!zend_hash_exists(EG(active_symbol_table), "a", sizeof("a"))) {
>        RETURN_BOOL(0);
>    }
>    RETURN_BOOL(1);
> }
> [/code]
>
> Note: the segfault only occurs when the sample_var_a_exists function  
> is called from within a userspace function:
>
> [code]
> $a = '';
> var_dump(sample_var_a_exists()); // bool(true)
>
> function x() {
>    var_dump(sample_var_a_exists()); // segmentation fault
> }
>
> x()

There is no symbol table as there are no variables. You should check  
if it's NULL before using zend_hash_exists.

Scott