linux-kernel - Re: [PATCH v2 14/22] arm64: Cleanup HWCAP handling

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Message-ID: <20151008111709.GE32532@n2100.arm.linux.org.uk>
Date:	Thu, 8 Oct 2015 12:17:09 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	"Suzuki K. Poulose" <suzuki.poulose@....com>, mark.rutland@....com,
	Vladimir.Murzin@....com, steve.capper@...aro.org,
	ard.biesheuvel@...aro.org, marc.zyngier@....com,
	andre.przywara@....com, will.deacon@....com,
	linux-kernel@...r.kernel.org, edward.nevill@...aro.org,
	aph@...hat.com, james.morse@....com, dave.martin@....com,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 14/22] arm64: Cleanup HWCAP handling

On Thu, Oct 08, 2015 at 12:10:00PM +0100, Catalin Marinas wrote:
> On Mon, Oct 05, 2015 at 06:02:03PM +0100, Suzuki K. Poulose wrote:
> > +static bool cpus_have_hwcap(const struct arm64_cpu_capabilities *cap)
> > +{
> > +	switch(cap->hwcap_type) {
> > +	case CAP_HWCAP:
> > +		return !!(elf_hwcap & cap->hwcap);
> > +#ifdef CONFIG_COMPAT
> > +	case CAP_COMPAT_HWCAP:
> > +		return !!(compat_elf_hwcap & (u32)cap->hwcap);
> > +	case CAP_COMPAT_HWCAP2:
> > +		return !!(compat_elf_hwcap2 & (u32)cap->hwcap);
> > +#endif
> > +	default:
> > +		BUG();
> > +		return false;
> > +	}
> > +}
> 
> Apart from the multiple returns, you don't really need !! since the
> return type is bool already.

That's wrong.  a & b doesn't return 0 or 1, but the bitwise-and result.

http://yarchive.net/comp/linux/bool.html

especially hpa's response.

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