Re: ref fix revisited

At 10:57 12/09/2005, Rasmus Lerdorf wrote:

Guys, could we take a look at making the ref to temp var fix a bit narrower? Currently we try to catch it at call-time. This means that something like: current(explode(' ','a b')) as per bug #34468 doesn't work. Now, I think there is a secondary bug here. I see no reason for current() to take a by-ref, so this particular one could be easily fixed.

Yep, we need to fix that one.

But there are many other cases where a function legitimately takes a by-ref and doesn't necessarily write to it or the write is a secondary action not required for the code to work. Could we not catch this on the write instead of on the call?

The problem is that there's no way to tell that element apart at that time. It's too late. As soon as we treat a read-only zval as if it's read/write (take a ** instead of a *), it's too late, since we can't really detect later on where it came from.

The memory problem happens on the write. Or perhaps better, an E_NOTICE or E_STRICT on the call and an E_FATAL on the write. The current E_FATAL on the call seems out of whack.

I don't really agree that it's out of whack, since you are passing a piece of data by reference, which is an undefined behavior. I agree that it would have been nice if we could allow for this and only complain if the data is written to in the function (in the PHP spirit of 'just work!'), but I don't see how that would be possible.

Gallery, for example, broke in a rather subtle way in their gallery_remote2.php script which meant the various client-side tools like iphototogallery and others got a cryptic "no album at URL" error message. I had to break out ethereal to track it down to a couple of functions where read-only function args were marked as by-ref. So they didn't actually have a memory corruption problem yet the E_FATAL killed them.

You'd have to agree that it is a bug on Gallery's part, though, right? If they're read only, they shouldn't have been marked as by-ref (yes, we screwed up by only introducing this error now after it worked for years, but it's still problematic to let it go on working and create possible corruption).

SquirrelMail has code like this all over the place: $value = strtolower(array_shift(split('/\w/',trim($value)))); Here array_shift() does of course change the arg, so that is a potential problem. And yes, that's a dumb way to do this, but people write code like this. In some of these array manipulation calls, which seems to account for a number of the BC problems we are having, we could check for a non-ref and behave slightly differently. In the case of array_shift() we could return the first arg and throw a notice. Same would go for reset(), end(), next(), prev() and probably a few others.

We could probably provide a way for internal functions to denote that they're handling by-ref 'wannabe' arguments, so that we won't generate a fatal error for them. We'd still have to do it for userland functions (and any other internal function). I'm not sure if it's worth it..? Zeev