linux-kernel - Re: using IS_ENABLED(CONFIG

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: <CAMuHMdVEK041TFY3JJ1kvYE_e_C72+FcRu3ewDipLPi-kN-h=A@mail.gmail.com>
Date:	Mon, 16 Nov 2015 09:28:09 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
Cc:	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Michal Marek <mmarek@...e.cz>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	arcml <linux-snps-arc@...ts.infradead.org>
Subject: Re: using IS_ENABLED(CONFIG_xyz) effectively

Hi Vineet,

On Mon, Nov 16, 2015 at 9:00 AM, Vineet Gupta
<Vineet.Gupta1@...opsys.com> wrote:
> I've been using IS_ENABLED for some time and once in a while run into an issue
> which prevents seamless use. Hence posing this question to experts in the area.
>
> C macro processor evaluates the ensuing control block even if IS_ENABLED evaluates
> to false. This requires dummy #defines or worse still removing usage of IS_ENABLED
> altogether.
>
> e.g. In example below even for ARCOMPACT builds, we need the ARCV2 specific define
> ARCV2_IRQ_DEF_PRIO.
>
> void arch_cpu_idle(void)
> {
>         if (is_isa_arcompact()) {    <---- IS_ENABLED(CONFIG_ISA_ARCOMPACT)
>                 __asm__("sleep 0x3");
>         } else {
>                 const int arg = 0x10 | ARCV2_IRQ_DEF_PRIO;
>                __asm__("sleep 0x10");
>         }
> }
>
> One could argue that the interface needs to be cleanly defined to not have such
> specific #defines in common code in first place. However sometime that becomes
> just too tedious.
>
> Is there a way to get around by this ?

Use #ifdef CONFIG_...?

The advantage of IS_ENABLED() over #ifdef is that it allows compile-testing of
the disabled code path. Of course it should only be compiled if it makes
sense. And that's exactly what you're running into.

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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/