Date: Mon, 25 Apr 2016 15:27:35 +0100
From: Mark Rutland <mark.rutland@arm.com>
To: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Robin Murphy <robin.murphy@arm.com>,
        "linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>,
        Russell King - ARM Linux <linux@arm.linux.org.uk>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Leif Lindholm <leif.lindholm@linaro.org>,
        "mingo@redhat.com" <mingo@redhat.com>, "hpa@zytor.com" <hpa@zytor.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCHv3 1/5] efi/runtime-wrappers: detect FW irq flag corruption
Message-ID: <20160425142735.GA14974@leverpostej>
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 <20160425141557.GA2829@codeblueprint.co.uk>
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On Mon, Apr 25, 2016 at 03:24:35PM +0100, Matt Fleming wrote:
> On Mon, 25 Apr, at 04:18:41PM, Ard Biesheuvel wrote:
> > On 25 April 2016 at 16:15, Matt Fleming <matt@codeblueprint.co.uk> wrote:
> > > On Mon, 25 Apr, at 03:12:01PM, Robin Murphy wrote:
> > >> >+static void efi_call_virt_check_flags(unsigned long flags, const char *call)
> > >> >+{
> > >> >+    unsigned long cur_flags;
> > >> >+    bool mismatch;
> > >> >+
> > >> >+    local_save_flags(cur_flags);
> > >> >+
> > >> >+    mismatch = !!((cur_flags ^ flags) & ARCH_EFI_IRQ_FLAGS_MASK);
> > >>
> > >> nit: the assignment itself is already a conversion to bool, so the
> > >> excitement is redundant here.
> > >
> > > This was intentional. I asked Mark to make this change so that it's
> > > explicit for the developer that we're performing the type conversion.
> > 
> > But replacing an implicit boolean cast with an explicit one makes
> > little sense, no? Don't we simply want '!= 0' here if you need a
> > boolean expression?
> 
> Aha but '!!' is fewer characters to type!!
> 
> I'm not that bothered as long as we don't stuff an int into a bool
> without giving the programmer some idea we're doing that. It's not
> about the compiler getting it wrong, more about a developer
> introducing a bug when they change the code in the future. 
> 
> Unless anyone objects, I'll fix this up to use '!= 0' when I apply it.

I have no strong preference so long as the code is correct.

Another option is to get rid of the bool entirely:

	flags ^= cur_flags;
	if (!WARN_ON(flags & ARCH_EFI_IRQ_FLAGS_MASK))
		return;

Mark.