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

[Adan Hawthorn]

On Thu, Feb 23, 2017 at 9:33 PM, Joe Perches  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).