Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754861AbcDYOdT (ORCPT ); Mon, 25 Apr 2016 10:33:19 -0400 Received: from eu-smtp-delivery-143.mimecast.com ([207.82.80.143]:53472 "EHLO eu-smtp-delivery-143.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754780AbcDYOdO convert rfc822-to-8bit (ORCPT ); Mon, 25 Apr 2016 10:33:14 -0400 Subject: Re: [PATCHv3 1/5] efi/runtime-wrappers: detect FW irq flag corruption To: Matt Fleming , Ard Biesheuvel References: <1461591994-14918-1-git-send-email-mark.rutland@arm.com> <1461591994-14918-2-git-send-email-mark.rutland@arm.com> <571E25B1.8070305@arm.com> <20160425141557.GA2829@codeblueprint.co.uk> <20160425142435.GB2829@codeblueprint.co.uk> CC: Mark Rutland , "linux-efi@vger.kernel.org" , Russell King - ARM Linux , Catalin Marinas , Will Deacon , "linux-kernel@vger.kernel.org" , Leif Lindholm , "mingo@redhat.com" , "hpa@zytor.com" , "tglx@linutronix.de" , "linux-arm-kernel@lists.infradead.org" From: Robin Murphy Message-ID: <571E2A9E.3010407@arm.com> Date: Mon, 25 Apr 2016 15:33:02 +0100 User-Agent: Mozilla/5.0 (X11; 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charset=WINDOWS-1252; format=flowed Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1975 Lines: 42 On 25/04/16 15:24, Matt Fleming wrote: > On Mon, 25 Apr, at 04:18:41PM, Ard Biesheuvel wrote: >> On 25 April 2016 at 16:15, Matt Fleming 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. Agreed - the belt and braces approach isn't necessarily bad if the cost of cocking it up is significant, and !=0 is as explicit as you can get. After all, if Joe Random Hacker can't infer the behaviour from looking 4 lines up to see the variable definition, then I wouldn't count on him understanding !! either ;) Thanks, Robin. 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