Fwd: Problem report: Struct aliasing problem causes Thread_Ready_Chain corruption in 4.6.99.3

[Ralf Corsepius]

On Tue, 2006-11-21 at 08:52 -0600, Joel Sherrill wrote:
> Ralf Corsepius wrote:
> > On Tue, 2006-11-21 at 13:38 +0100, Thomas Doerfler wrote:
> >
> >   
> >> I found a good discussion about GCC and strict aliasing here:
> >>
> >> http://www.cellperformance.com/mike_acton/2006/06/understanding_strict_aliasing.html
> >>
> >> Maybe it would help to modify the definition of Chain_Ctronol to
> >> something like:
> >>
> >> typedef union {
> >>   struct {
> >>     struct Chain_Node_struct head;
> >>     void *fill_loc1;
> >>   } head_node;
> >>
> >>   struct {
> >>     void *fill_loc1;
> >>     struct Chain_Node_struct tail;
> >>   } tail_node;
> >> } Chain_Control;
> >>
> >> The names are NOT good, and surely all chain.c/chain.inl functions would
> >> have to be adapted but this might be a mechanical search/replace procedure.
> >>
> >> Any comments to a change like this?
> >>     
> Using a union like this would probably remove a lot of casts and could
> make the code easier to read.
It's "'em casts" which are the origin of this evil!
 
> I would want to be careful about the names.  And the changes do extend
> a bit out of the chain code.  There are a few places which explicitly do
> casts to (Chain_Node *) which could be cleaned up.
Remove these casts and eliminate the "punned warnings" without using
explict casts. In 90% of all cases all you'll probably need to solve the
issue is a temporary pointer.

Ralf