linux-kernel - Re: [PATCH 01/17] bitfield: Add non-constant field

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <CAMuHMdX4C0EgkGXR=MwSuBOFoj7O9xx8xwH5dP8rWzN1ckejQA@mail.gmail.com>
Date:   Tue, 23 Nov 2021 09:38:51 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Alex Elder <elder@...e.org>
Cc:     Johannes Berg <johannes@...solutions.net>,
        Tony Lindgren <tony@...mide.com>,
        Russell King <linux@...linux.org.uk>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Paul Walmsley <paul@...an.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Ludovic Desroches <ludovic.desroches@...rochip.com>,
        Tero Kristo <kristo@...nel.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Lorenzo Bianconi <lorenzo.bianconi83@...il.com>,
        Benoit Parrot <bparrot@...com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Andrew Jeffery <andrew@...id.au>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Joel Stanley <joel@....id.au>,
        Ping-Ke Shih <pkshih@...ltek.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Magnus Damm <magnus.damm@...il.com>,
        Eduardo Valentin <edubezval@...il.com>,
        Keerthy <j-keerthy@...com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Amit Kucheria <amitk@...nel.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        linux-arm-kernel@...ts.infradead.org, linux-omap@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, linux-iio@...r.kernel.org,
        linux-media@...r.kernel.org, linux-mmc@...r.kernel.org,
        linux-aspeed@...ts.ozlabs.org, openbmc@...ts.ozlabs.org,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-gpio@...r.kernel.org, linux-pm@...r.kernel.org,
        alsa-devel@...a-project.org
Subject: Re: [PATCH 01/17] bitfield: Add non-constant field_{prep,get}() helpers

Hi Alex,

On Tue, Nov 23, 2021 at 2:52 AM Alex Elder <elder@...e.org> wrote:
> On 11/22/21 10:32 AM, Johannes Berg wrote:
> > On Mon, 2021-11-22 at 16:53 +0100, Geert Uytterhoeven wrote:
> >> The existing FIELD_{GET,PREP}() macros are limited to compile-time
> >> constants.  However, it is very common to prepare or extract bitfield
> >> elements where the bitfield mask is not a compile-time constant.
> >
> > I'm not sure it's really a good idea to add a third API here?
> >
> > We have the upper-case (constant) versions, and already
> > {u32,...}_get_bits()/etc.
>
> I've used these a lot (and personally prefer the lower-case ones).
>
> Your new macros don't do anything to ensure the field mask is
> of the right form, which is basically:  (2 ^ width - 1) << shift

> I really like the property that the field mask must be constant.

That's correct. How to enforce that in the non-const case?
BUG()/WARN() is not an option ;-)

> That being said, I've had to use some strange coding patterns
> in order to adhere to the "const only" rule in a few cases.
> So if you can come up with a satisfactory naming scheme I'm
> all for it.

There are plenty of drivers that handle masks stored in a data
structure, so it would be good if they can use a suitable helper,
as open-coding is prone to errors.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds