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Date: Tue, 21 Feb 2006 15:08:07 -0800
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To: Nuno Lopes <nlopess@php.net>
CC: PHPdev <internals@lists.php.net>
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Subject: Re: [PHP-DEV] recover from a segfault
From: rasmus@lerdorf.com (Rasmus Lerdorf)

Nuno Lopes wrote:
> Hi,
> 
> In the last days I've exchanged some e-mails with PCRE's author because 
> of one more bug that appeared in our database about segfaults in PCRE 
> (related to stack overflows).
> PCRE can consume a lot of stack, because of backtracking (thus 
> segfaulting PHP). Yesterday I've discovered that when using the 
> setrlimit() function, most segfaults can be avoided 
> (http://mega.ist.utl.pt/~ncpl/php_pcre_stack_limits.txt)  :)
> 
> But I was thinking why we can't fail more silently from segfaults. A 
> recursive PHP function can easily segfault PHP. Why can't we catch the 
> signal and recover from the error? (and print a "stack overflow" 
> message, like java does).

Because catching these kinds of signals is a nightmare.  In this 
particular instance it may work because your stack hasn't been trashed, 
but in many other cases it simply isn't safe to try to execute further 
code.  I don't know how many times I have had to go through and get rid 
of some programmer's misguided idea that trying to catch and handle a 
SEGV nicely was a good idea.  An infinitely chain of segfaults in your 
segfault handler is impossible to avoid and is much much worse than just 
dropping a core as fast as possible and exiting.  Any such handler also 
tends to obscure the actual problem making it much more difficult to 
examine the core file later.

-Rasmus