RE: [csmith-project/csmith] 717b1c: Fixed a bug related to --no-math64 and --no-longlo...

["Xuejun Yang" <jxyang@cs.utah.edu>]

My memory is a little fuzzy on our last conversation about unions. But I think applying these 2 constraints on unions accesses could avoid undefined behaviors caused by padding bits:

1) after writing a field, reading must be through a field of equal or smaller size. i.e., writing to a int field and then reading from a char field is fine, but not the other way around.
 
2) after writing a struct field, reading must the through the same field.

I think with those we can avoid undefined behaviors without getting into messy details of types. Did I miss anything?

-Xuejun  

> 
> But you're going to need alignment information for everything to make
> unions work, right?
> 
> John
> 
> 
> On 05/04/2011 06:58 PM, Xuejun Yang wrote:
> > Yes, if we fix-size integers, the only thing left is pointers. That's why I was
> asking. Well, I can fix it to 8 bytes for now if only unions care about it.
> >
> > -Xuejun
> >
> >> -----Original Message-----
> >> From: csmith-commits-bounces@flux.utah.edu
> >> [mailto:csmith-commits-bounces@flux.utah.edu] On Behalf Of John Regehr
> >> Sent: Wednesday, May 04, 2011 6:53 PM
> >> To: csmith-commits@flux.utah.edu
> >> Subject: Re: [csmith-project/csmith] 717b1c: Fixed a bug related to
> --no-math64
> >> and --no-longlo...
> >>
> >> Ok sorry to yell.
> >>
> >> I grepped for x86_64 and it's not used much, so should be easy to eliminate.
> >>
> >> Xuejun: are you going to need size/alignment information to make unions
> >> work?  For example, to avoid accessing padding bytes?
> >>
> >> John
> >