PHP 4.0 Bug #9136 Updated: simple script with infinite function calls causes seg fault

ID: 9136 User Update by: nathan@synop.com Old-Status: Feedback Status: Open Bug Type: Feature/Change Request Description: simple script with infinite function calls causes seg fault I agree that recursion like this is not a good thing, it was an accidental bug in a very complex PHP module we were writing. The problem is that it's an incredibly difficult bug to find when PHP just seg faults and you get a No Data error from Netscape. When you are coding a very complex module as we were, the problem is not immediately obvious as in this example. I would expect buggy PHP code like this to give me a stack overflow error report or execution time exceeded error or something. I just sat there for about 5 minutes going WHAT!?!?! when I made a set of changes and suddenly PHP started seg faulting all over the place. I agree that an ini setting to check the stack level against a maximum sounds like a good idea. I think it would be good to have on by default (not just safe mode) given that many PHP developers are new programmers who can easily make recursion mistakes (not to mention more experienced php coders like me who still easily make recursion mistakes ;). Just set the value to something large enough to catch these recursion bugs without effecting the running of most normal recursive applications. True maniacs can turn it off by setting to -1 or something. I prefer to be protected from myself until I'm ready to grow out of the protection... <grin> Previous Comments: --------------------------------------------------------------------------- [2001-02-06 17:41:12] waldschrott@php.net maybe we should move this to feature request for safe mode? it would be fine to give the server owner the possibility to autokill scripts which would kill the server in a few microseconds, shouldn't it be implementable without loosing performance, check the level the stack is filled up against a values in php.ini maybe... --------------------------------------------------------------------------- [2001-02-06 17:31:02] waldschrott@php.net and guess this "bug" was present in any version before, what do you expect to happen here? you will never leave these function calls (as you know I guess), as far as your stack is full it is full remember php has to remember each and every function call it did... a() b() a() b() .... if you really need exactly this construct, I would suggest you to use a static variable to count the total function calls and find the critical values a specific system segfaults (with your original code), then you stick a for(;;) around it and implement a check (eg. in a()) against the static variable to leave the recursion if a value with enough distance to the critical value is reached, then you should be able to begin the recursion again any recursion can be displayed as a loop, do not use recursion if you want to recurse infinitely --------------------------------------------------------------------------- [2001-02-06 17:22:36] derick@php.net PHP doesn't handle infinite recursion, and as earlier was discussed on the php-dev list, it wont be implemented to guard for this, because of the high performance impact. --------------------------------------------------------------------------- [2001-02-06 17:18:03] nathan@synop.com ------------------- <% function a () { b(); } function b () { a(); } a(); %> <h1>done</h1> --------------------- The simple script above causes a seg fault. If you need more info on configuration etc please mail me. We made this simple example from a more compilcated instance. This bug was also present in 4.0.3pl1, we upgraded to try and stop the seg fault... thanks! --------------------------------------------------------------------------- Full Bug description available at: http://bugs.php.net/?id=9136