Re: [PATCH v4 01/17] x86/mpx: Do not use SIB index if index points to R/ESP

On Feb 23, 2017 9:33 PM, "Joe Perches" <[email protected]> wrote:

On Thu, 2017-02-23 at 14:17 -0800, Ricardo Neri wrote:
> On Thu, 2017-02-23 at 08:24 +0100, Peter Zijlstra wrote:
> > On Wed, Feb 22, 2017 at 10:36:50PM -0800, Ricardo Neri wrote:
> > > +                 /*
> > > +                  * A negative offset generally means a error, except
> > > +                  * -EDOM, which means that the contents of the
register
> > > +                  * should not be used as index.
> > > +                  */
> > >                   if (indx_offset < 0)
> > > -                         goto out_err;
> > > +                         if (indx_offset == -EDOM)
> > > +                                 indx = 0;
> > > +                         else
> > > +                                 goto out_err;
> > > +                 else
> > > +                         indx = regs_get_register(regs, indx_offset);
> >
> > Kernel coding style requires more brackets than are strictly required by
> > C, any block longer than 1 line needs then. Also, if one leg of a
> > conditional needs them, then they should be on both legs.
> >
> > Your code has many such instances, please change them all.
>
> Will do. Sorry for the noise. These instances escaped the checkpatch
> script.

Also, this code would read better with the inner test
reversed or done first

                if (indx_offset < 0) {
                        if (indx_offset != -EDOM)
                                goto out_err;
                        indx = 0;
                } else {
                        indx = regs_get_register(etc...)
                }

or
                if (indx_offset == -EDOM)
                        indx = 0;
                else if (indx_offset < 0)
                        goto err;


Or goto out_err;

                else
                        indx = regs_get_register(etc...)

The compiler should generate the same code in any
case, but either could improve reader understanding.


Also, it may be a tweak more efficient to handle the most likely runtime
case in the conditional stack first (whichever that may be).