Re: [PATCH v2 1/3] overflow.h: Add arithmetic shift helper

[Kees Cook]

On Wed, Aug 1, 2018 at 1:07 AM, Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote:
> On Wed, Aug 01, 2018 at 10:57:44AM +0300, Dan Carpenter wrote:
>> The idea is nice, but I don't like the API.  The "_overflow" feels too
>> specific because maybe we could check for other things in the future.
>> Normally boolean macros should say they are boolean in the name and I
>> would prefer if it returned zero on failure.
>>
>>       if (!checked_shift(dest, mask, shift)) {
>>       if (!shift_ok(dest, mask, shift)) {
>>       if (!safe_shift(dest, mask, shift)) {
>
> Huh...  It turns out I put the argument order different as well.
>
> If we wanted to keep it returning 1 on failure then some other names
> are:
>
>         if (shift_failed(dest, mask, shift)) {
>         if (shift_error(dest, mask, shift)) {
>         if (shift_overflow(dest, mask, shift)) {

This is following the existing check_{add,mul}_overflow() helpers,
which are based on the gcc helpers. I'd like to keep things
consistent.

-Kees

-- 
Kees Cook
Pixel Security