Re: Back branches vs. gcc 4.8.0

On 2013-04-29 23:37:43 -0400, Peter Eisentraut wrote:
> On Sat, 2013-04-06 at 12:59 -0400, Tom Lane wrote:
> > The reason I'm thinking it's a good idea is that it would expose any
> > remaining places where we have nominally var-length arrays embedded in
> > larger structs. Now that I've seen the failures with gcc 4.8.0, I'm
> > quite worried that there might be some more declarations like that
> > which we've not identified yet, but that by chance aren't causing
> > obvious failures today.
>
> Here is a rough patch that replaces almost all occurrences of
> something[1] in a struct with FLEXIBLE_ARRAY_MEMBER. It crashes left
> and right (because of sizeof issues, probably), but at least so far the
> compiler hasn't complained about any flexible-array members not at the
> end of the struct, which is what it did last time. So the answer to
> your concern so far is negative.

I think this point in the cycle would be a good one to apply something
like this.

> Completing this patch will be quite a bit more debugging work. Some
> kind of electric fence for palloc would be helpful.

Noah's recently added valgrind mode should provide this.

Do you have an updated version of this patch already? I'd be willing to
make a pass over it to check whether I find any missed updates...

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services