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From: Mark Rutland <mark.rutland@arm.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Joe Richey <joerichey94@gmail.com>,
	trivial@kernel.org, Joe Richey <joerichey@google.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Zhangfei Gao <zhangfei.gao@linaro.org>,
	Zhou Wang <wangzhou1@hisilicon.com>,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-media@vger.kernel.org, linux-accelerators@lists.ozlabs.org
Subject: Re: [PATCH 0/6] Don't use BIT() macro in UAPI headers
Date: Mon, 24 May 2021 13:29:01 +0100	[thread overview]
Message-ID: <20210524122901.GH1040@C02TD0UTHF1T.local> (raw)
In-Reply-To: <YKuSEnfEbjpOOgLS@infradead.org>

On Mon, May 24, 2021 at 12:46:26PM +0100, Christoph Hellwig wrote:
> On Thu, May 20, 2021 at 03:43:37AM -0700, Joe Richey wrote:
> > This patch series changes all UAPI uses of BIT() to just be open-coded.
> > However, there really should be a check for this in checkpatch.pl
> > Currently, the script actually _encourages_ users to use the BIT macro
> > even if adding things to UAPI.
> 
> Yes.  In fact it should warn about BIT() in general.  It is totally
> pointless obsfucation that doesn't even save any typing at all.

That's not quite true; the point is that if you use BIT() consistently,
then even when you refer to bits 32 to 63 you won't accidentally
introduce shifts of more than the width of int, and the definition will
work equally well for assembly and C, which isn't true if you use `1UL`
in the definition.

With that in mind it's shorter and clearer than its functional
equivalent:

  BIT(x)
  (UL(1) << (x))

So IMO it's preferable to use BIT() generally, or _BITUL() in uapi
headers.

Thanks,
Mark.

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  reply	other threads:[~2021-05-24 18:52 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-20 10:43 Joe Richey
2021-05-20 10:43 ` [PATCH 1/6] x86/elf: " Joe Richey
2021-05-20 10:43 ` [PATCH 2/6] KVM: X86: " Joe Richey
2021-05-20 15:46   ` Sean Christopherson
2021-05-20 10:43 ` [PATCH 3/6] drivers: firmware: psci: " Joe Richey
2021-05-20 10:43 ` [PATCH 4/6] uacce: " Joe Richey
2021-05-20 10:43 ` [PATCH 5/6] media: vicodec: " Joe Richey
2021-05-20 10:43 ` [PATCH 6/6] tools headers UAPI: Sync pkt_sched.h with the kernel sources Joe Richey
2021-05-20 11:07 ` [PATCH 0/6] Don't use BIT() macro in UAPI headers Borislav Petkov
2021-05-20 11:50   ` Joseph Richey
2021-05-20 15:59     ` Borislav Petkov
2021-05-20 15:50   ` Sean Christopherson
2021-05-20 11:11 ` Mark Rutland
2021-05-20 11:40   ` Joseph Richey
2021-05-20 12:09 ` Paolo Bonzini
2021-05-20 15:47 ` Sean Christopherson
2021-05-21  8:58 ` [PATCH v2 0/7] " Joe Richey
2021-05-21  8:58   ` [PATCH v2 1/7] x86/elf: Use _BITUL() " Joe Richey
2021-05-21  8:58   ` [PATCH v2 2/7] KVM: X86: " Joe Richey
2021-05-24 12:28     ` Paolo Bonzini
2021-05-21  8:58   ` [PATCH v2 3/7] drivers: firmware: psci: " Joe Richey
2021-05-21 13:25     ` Mark Rutland
2021-05-21  8:58   ` [PATCH v2 4/7] uacce: " Joe Richey
2021-05-21 13:56     ` Zhangfei Gao
2021-05-21  8:58   ` [PATCH v2 5/7] media: vicodec: " Joe Richey
2021-05-21  8:58   ` [PATCH v2 6/7] tools headers UAPI: Sync pkt_sched.h with the kernel sources Joe Richey
2021-05-21  8:58   ` [PATCH v2 7/7] checkpatch: suggest _BITULL() and _BITUL() for UAPI headers Joe Richey
2021-05-21 14:45     ` Joe Perches
2021-05-24 11:46 ` [PATCH 0/6] Don't use BIT() macro in " Christoph Hellwig
2021-05-24 12:29   ` Mark Rutland [this message]
2021-05-24 16:34     ` David Laight

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