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Subject: Re: alloca() problem
From: abies@php.net (Ard Biesheuvel)

Ilia Alshanetsky wrote:
> There is a rather nasty crash possible in PHP due to the usage of the alloca() 
> function as can be demonstrated by bug #28064.
> Simpler bug replication case:
> php -r ' $a = str_repeat("a", 1024 * 1024 * 6); defined($a); '
> 

The following two fragments will lead to virtually identical code:

     void foo()
     {
         char bar[2048];
         ...
     }

and

     void foo()
     {
         char *bar = alloca(2048);
         ....

They both start out by moving the stack pointer down 2k to leave enough 
room for bar, and they will both crash in a similar way if the stack 
doesn't have enough room available.

I think that not alloca() itself but its improper use is the problem 
here. Any function will cause a crash if you call it when your stack is 
full.  Just be sensible about when (not to) use it.

-- 
Ard