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From:   Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date:   Tue, 28 May 2019 17:51:51 +0200
Message-ID: <CAKv+Gu8bReGWAUm4GrCg7kefVR7U0Z8XBt_GVV4WEvgOpCtjpA@mail.gmail.com>
Subject: Re: Conding style question regarding configuration
To:     Pascal Van Leeuwen <pvanleeuwen@insidesecure.com>
Cc:     "linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>
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On Tue, 28 May 2019 at 17:47, Pascal Van Leeuwen
<pvanleeuwen@insidesecure.com> wrote:
>
> Hi,
>
> Quick question regarding how to configure out code depending on a CONFIG_xxx
> switch. As far as I understood so far, the proper way to do this is not by
> doing an #ifdef but by using a regular if with IS_ENABLED like so:
>
> if (IS_ENABLED(CONFIG_PCI)) {
> }
>
> Such that the compiler can still check the code even if the switch is
> disabled. Now that all works fine and dandy for statements within a
> function, but how do you configure out, say, global variable definitions
> referencing types that are tied to this configuration switch? Or should
> I just leave them in, depending on the compiler to optimize them away?
>
> Obviously the code depends on those variables again, so if it's not
> done consistently the compiler will complain somehow if the switch is not
> defined ...
>
> Also, with if (IS_ENABLED()) I cannot remove my function prototypes,
> just the function body. Is that really how it's supposed to be done?
>

Yes. Code and data with static linkage will just be optimized away by
the compiler if the CONFIG_xx option is not enabled, so all you need
to guard are the actual statements, function calls etc.