ID: 9136
User Update by: [EMAIL PROTECTED]
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:
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[2001-02-06 17:41:12] [EMAIL PROTECTED]
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] [EMAIL PROTECTED]
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] [EMAIL PROTECTED]
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] [EMAIL PROTECTED]
-------------------
<%
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!
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Full Bug description available at: http://bugs.php.net/?id=9136
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