[RFC] SysV SHM on 64-bit platforms

[David Schultz]

On Mon, Jan 21, 2008, Jung-uk Kim wrote:
> On Saturday 19 January 2008 07:13 am, David Schultz wrote:
> > For 8-CURRENT, I'd say go ahead and fix it and add the syscall
> > compat goop. Then I guess backport it to 7-STABLE after a while if
> > nothing important breaks and nobody has any objections to that
> > plan.
> 
> Well, since the policy is 'no seat belt for -CURRENT', I think that is 
> aceptable, too.

Right, but you need the compat shims to avoid breaking the ABI
when 8.0 is released anyway.

> > It would also be cool if struct ipcperm got fixed at the same time
> > so we only have to do this once. I think that only entails adding
> > compat crud to semctl and maybe one or two other syscalls. Those
> > changes aren't urgent enough to make it worthwhile to backport to
> > 7.X IMO, though.
> 
> So, you are in between option 1 and 4, i.e., bigger fix goes to HEAD 
> and partial MFC to RELENG_7, right?

I'd say try to fix everything once and for all in HEAD, including
struct ipcperm, but only MFC the shmid_ds changes to minimize the
chance that anything breaks between 7.X releases. Others may have
different opinions...

> Actually, the arch check is 
> done like this:
> 
> if (sizeof(size_t) != sizeof(int) && td->td_proc->p_osrel <= WHATEVER)
> 
> I am hoping the compiler is smart enough to optimize away 
> 'sizeof(size_t) != sizeof(int)'.

Yes, gcc does basic dead code elimination like this at all
optimization levels, including -O0. Of course the code within the
if block still has to be syntactically valid on all architectures;
if it isn't, then you need ifdefs.

> > - The 8.X version needs to take the p_osrel for the equivalent
> >   change in 7.X into account.
> 
> I thought it did, didn't it?

Oops, maybe you did and I was looking at one of the other versions
of the patch.