CODEWITHSUNDEEP
phpsegmentation-fault
freddiefujiwara
freddiefujiwara

Reputation: 59089

Why does this PHP function give a segmentation fault (SIGSEGV)?

I wrote the following code.

<?php
function f(){
  return f();
}
f();

and get the output

$ php test.php
Segmentation fault

Why? I didn't use any pointers.

This is StackOverflow ?

Upvotes: 3

Views: 5704

Answers (4)

netcoder
netcoder

Reputation: 67745

This comes specifically from the XDebug extension.

Running GDB, you will see:

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff41f7e48 in xdebug_add_stack_frame (zdata=Cannot access memory at address 0x7fffff5fefa8
) at /build/buildd/xdebug-2.1.0/build-php5/xdebug_stack.c:772
772 /build/buildd/xdebug-2.1.0/build-php5/xdebug_stack.c: No such file or directory.
    in /build/buildd/xdebug-2.1.0/build-php5/xdebug_stack.c

If XDebug is disabled, it will execute until the memory_limit is reached. If your memory_limit is too high, you might exhaust RAM and start swapping, freezing/crashing your machine.

Upvotes: 1

hashwarp
hashwarp

Reputation: 3933

This is a case of infinite recursion, but that is not specifically the cause. It is a stack overflow. When you have recursion, whether infinite or not, there is a max amount of depth you can recurse (add to the stack) which is based on the size of your stack (in bytes).

Technically this is infinite, but you won't get any errors for quite a while:

<?php
function f(){
  sleep(1);
  return f();
}
f();

What you need is known as a base case in your recursion in order to stop it before it consumes the entire stack.

<?php
function f($i){
  if($i == 10)
    return;

  echo $i;

  return f(++$i);
}
f(0);

Which will print 0 to 9.

The segmentation fault error is coming from the operating system, reporting the PHP application has encountered an issue adding to the stack. That won't make it to your script because at the system level the binary which makes up PHP has failed.

Upvotes: 7

Tom
Tom

Reputation: 1339

The infinite recursion you've set up continues to add stack frames until you overrun the amount of memory assigned to the PHP process call stack, at which point you get a segmentation fault.

Upvotes: 0

Vern
Vern

Reputation: 2413

Isn't that an infinite recursion? What're you trying to achieve?

Upvotes: 1

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