linux-kernel - Re: [PATCH v4 2/6] treewide: use prandom_u32

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Message-ID: <alpine.DEB.2.22.394.2210080925390.2928@hadrien>
Date:   Sat, 8 Oct 2022 09:33:08 +0200 (CEST)
From:   Julia Lawall <julia.lawall@...ia.fr>
To:     Kees Cook <keescook@...omium.org>
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Subject: Re: [PATCH v4 2/6] treewide: use prandom_u32_max() when possible

> >> @minus_one@
> >> expression FULL;
> >> @@
> >>
> >> - (get_random_int() & ((FULL) - 1)
> >> + prandom_u32_max(FULL)
> >
> >Ahh, well, okay, this is the example I mentioned above. Only works if
> >FULL is saturated. Any clever way to get coccinelle to prove that? Can
> >it look at the value of constants?
>
> I'm not sure if Cocci will do that without a lot of work. The literals trick I used below would need a lot of fanciness. :)

If FULL is an arbitrary expression, it would not be easy to automate.  If
it is a constant then you can use python/ocaml to analyze its value.  But
if it's a #define constant then you would need a previous rule to match the
#define and find that value.

For LITERAL, I think you could just do constant int LITERAL; for the
metavariable declaration.

julia