+Cc: Rasmus as he has done a lot regarding library stuff and optimizations and
he knows Coccinelle (to some extent as far as I can tell).
On Wed, Oct 26, 2022 at 02:58:34PM +0200, Jason A. Donenfeld wrote:
> On Wed, Oct 26, 2022 at 03:50:25AM +0200, Jason A. Donenfeld wrote:
> > The traditional objdump comparison does work, though. It produces a good
>
> Another thing that appears to work well is just using Coccinelle
> scripts. I've had some success just scrolling through the results of:
>
> @@
> char c;
> expression E;
> @@
> (
> * E > c
> |
> * E >= c
> |
> * E < c
> |
> * E <= c
> )
>
> That also triggers on explicitly signed chars, and examining those
> reveals that quite a bit of code in the tree already does do the right
> thing, which is good.
>
> From looking at this and objdump output, it looks like most naked-char
> usage that isn't for strings is actually already assuming it's unsigned,
> using it as a byte. I'll continue to churn, and I'm sure I'll miss a few
> things here and there, but all and all, I don't think this is looking as
> terrible as I initially feared.
>
> I'm CC'ing the Coccinelle people to see if they have any nice ideas on
> improvements. Specifically, the thing we're trying to identify is:
>
> - Usage of vanilla `char`, without a `signed` or `unsigned` qualifier,
> where:
> - It's not being used for characters; and
> - It's doing something that assumes it is signed, such as various
> types of comparisons or decrements.
>
> LWN wrote a summary of the general problem, in case that helps describe
> what would be useful: https://lwn.net/SubscriberLink/911914/f90c2ed1af23cbc4/
>
> Any nice Cocci tricks for this?
--
With Best Regards,
Andy Shevchenko
