linux-kernel - Re: [PATCH v4 2/2] linux/bits.h: simplify GENMASK_INPUT

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAMZ6RqJwSf9L8sSA78uaizdqNDa__Xz7WY+g5yNgs62Sx-WUog@mail.gmail.com>
Date: Mon, 18 Nov 2024 10:12:45 +0900
From: Vincent Mailhol <mailhol.vincent@...adoo.fr>
To: David Laight <David.Laight@...lab.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>, Yury Norov <yury.norov@...il.com>, 
	Rasmus Villemoes <linux@...musvillemoes.dk>, Luc Van Oostenryck <luc.vanoostenryck@...il.com>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"linux-sparse@...r.kernel.org" <linux-sparse@...r.kernel.org>, 
	Rikard Falkeborn <rikard.falkeborn@...il.com>
Subject: Re: [PATCH v4 2/2] linux/bits.h: simplify GENMASK_INPUT_CHECK()

On Mon. 18 Nov. 2024 at 02:24, David Laight <David.Laight@...lab.com> wrote:
> From: Vincent Mailhol
> > Sent: 13 November 2024 17:19
> >
> > In GENMASK_INPUT_CHECK(),
> >
> >   __builtin_choose_expr(__is_constexpr((l) > (h)), (l) > (h), 0)
> >
> > is the exact expansion of:
> >
> >   const_true((l) > (h))
> >
> > Apply const_true() to simplify GENMASK_INPUT_CHECK().
>
> Wouldn't statically_true() give better coverage ?
> I wouldn't have though that GENMASK() got used anywhere where a constant
> integer expression was needed.
>
> More interesting would be to get it to pass a W=1 build for
> any place where 'l' is 0u.

Are you referring to -Wtype-limits? If yes, this warning was moved to
W=2. I suggested in the past to add a cast to silence this warning,
but got rejected:

  https://lore.kernel.org/lkml/CAHk-=whvGWbpsTa538CvQ9e=VF+m8WPQmES2y6-=0=-64uGkgg@mail.gmail.com/

Yours sincerely,
Vincent Mailhol