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 <joe@xxxxxxxxxxx> 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).