Re: [PATCH 2.6.13-rc1 07/10] IOCHK interface for I/O error handling/detecting

[Jesse Barnes <jesse.barnes@intel.com>]

On Friday, July 8, 2005 1:17 pm, Luck, Tony wrote:
> >I don't think this is really safe.  There is nothing to stop the
> >compiler from loading the value directly into the out register,
> > which would again defer consumption of the value (especially if the
> > caller of ia64_mca_barrier() got inlined itself.
>
> I'd thought that the value needs to go to both the "out" register,
> and to "r8" to be returned from the function ... but you are right,
> this can be by-passed if the function that calls ia64_mca_barrier is
> itself inlined.
>
> >In my opinion, it would be safest to write this in assembly, so
> > we're _guaranteed_ it will do what we want, no matter how smart the
> > compilers get.  Something along the lines of:
> >
> >ia64_mca_barrier:
> >   mov r8 = r32
> >   br.ret.sptk.many rp
> >
> >should do (and I agree that this function needs a comment).
>
> So are you envisioning using it like this?
>
> 	val = ia64_mca_barrier(*(type *)ioaddr);

Why not be extra safe and call PAL_MC_FLUSH?  Or would that be too 
expensive?

Jesse