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: <20211124055935.416dc472@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Wed, 24 Nov 2021 05:59:35 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        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>,
        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

On Wed, 24 Nov 2021 09:03:24 +0100 Johannes Berg wrote:
> On Tue, 2021-11-23 at 15:49 -0800, Jakub Kicinski wrote:
> > > Indeed.
> > > 
> > > Also as I said in my other mail, the le32/be32/... variants are
> > > tremendously useful, and they fundamentally cannot be expressed with the
> > > FIELD_GET() or field_get() macros. IMHO this is a clear advantage to the  
> > 
> > Can you elaborate?  
> 
> Well, the way I see it, the only advantage of FIELD_GET() is that it
> will auto-determine the type (based on the mask type.) This cannot work
> if you need be/le conversions, because the be/le type annotations are
> invisible to the compiler.
> 
> So obviously you could write a BE32_FIELD_GET(), but then really that's
> equivalent to be32_get_bits() - note you you have to actually specify
> the type in the macro name. I guess in theory you could make macros
> where the type is an argument (like FIELD_GET_TYPE(be32, ...)), but I
> don't see how that gains anything.

Ah, that's what you meant! Thanks for spelling it out.

FWIW I never found the be/le versions useful. Most of the time the data
comes from bus accessors which swap or is unaligned so you have to do
be/le_get_unaligned, which swaps. Plus if you access/set multiple
fields you'd swap them one by one which seems wasteful.

> > > typed versions, and if you ask me we should get rid of the FIELD_GETand
> > > FIELD_PREP entirely - difficult now, but at least let's not propagate
> > > that?  
> > 
> > I don't see why.  
> 
> Just for being more regular, in the spirit of "there's exactly one
> correct way of doing it" :)

Right now it seems the uppercase macros are more prevalent.

Could just be because of the way the "swapping ones" are defined.