Re: unaligned memory access & SIGBUS

[Jean-Yves Migeon <jeanyves.migeon%free.fr@localhost>]

Le 11/04/12 17:42, Nicolas Joly a écrit :
> > > njoly@lanfeust [tmp/malign]>  uname -a
> > > NetBSD lanfeust.sis.pasteur.fr 6.99.4 NetBSD 6.99.4 (LANFEUST) #2: Mon
> > > Apr  9 23:30:03 CEST 2012
> > > njoly%lanfeust.sis.pasteur.fr@localhost:/local/src/NetBSD/obj.amd64/sys/arch/amd64/compile/LANFEUST
> > >  amd64
> > > njoly@lanfeust [tmp/malign]>  cc -o malign malign.c
> > > njoly@lanfeust [tmp/malign]>  ./malign
> > > 0
> [...]
> > PSL_AC needs to be part of PSL_USER?
>
> Thanks for the tip, but simply adding it to PSL_USER do not change
> anything; still no SIGBUS signal.
>
> Unless someone beats me ;) i'll need to find some spare to understand
> that part of code hoping to see what's going on.

FWIW I talked with Nicolas about this privately, and the fix is fairly 
straightforward once you know it: alignment checks only trap when the 
CR0_AM bit is set in %cr0. Our code does not set it, so the CPU does not 
trap AE.

I have a patch ready for it, will commit it after I convert its malign.c 
test to an ATF one.

I will ask for a pull-up, the patch is rather harmless.

--
jym@