linux-kernel - Re: [PATCH 02/18] arm64: move SCTLR_EL{1,2} assertions to <asm/sysreg.h>

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Date:   Mon, 14 May 2018 11:08:59 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Dave Martin <Dave.Martin@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, marc.zyngier@....com,
        catalin.marinas@....com, will.deacon@....com,
        linux-kernel@...r.kernel.org, linux@...inikbrodowski.net,
        james.morse@....com, viro@...iv.linux.org.uk,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 02/18] arm64: move SCTLR_EL{1,2} assertions to
 <asm/sysreg.h>

On Mon, May 14, 2018 at 11:00:53AM +0100, Dave Martin wrote:
> On Mon, May 14, 2018 at 10:46:24AM +0100, Mark Rutland wrote:
> > -/* Check all the bits are accounted for */
> > -#define SCTLR_EL2_BUILD_BUG_ON_MISSING_BITS	BUILD_BUG_ON((SCTLR_EL2_SET ^ SCTLR_EL2_CLEAR) != ~0)
> > -
> > +#if (SCTLR_EL2_SET ^ SCTLR_EL2_CLEAR) != 0xffffffff
> > +#error "Inconsistent SCTLR_EL2 set/clear bits"
> > +#endif
> 
> Can we have a comment on the != 0xffffffff versus != ~0 here?
> 
> The subtle differences in evaluation semantics between #if and
> other contexts here may well trip people up during maintenance...

Do you have any suggestion as to the wording?

I'm happy to add a comment, but I don't really know what to say.

Thanks,
Mark.