linux-kernel - RE: [PATCH] usbhid: Fix lockdep unannotated irqs-off warning

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Date:	Mon, 7 Mar 2016 13:07:33 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	David Laight <David.Laight@...LAB.COM>
cc:	"'sedat.dilek@...il.com'" <sedat.dilek@...il.com>,
	Jiri Kosina <jikos@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Tejun Heo <tj@...nel.org>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Benjamin Tissoires <benjamin.tissoires@...hat.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Andy Lutomirski <luto@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	USB list <linux-usb@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: RE: [PATCH] usbhid: Fix lockdep unannotated irqs-off warning

On Mon, 7 Mar 2016, David Laight wrote:

> From: Sedat Dilek
> ...
> > Did someone look at the next/follow-ups in this thread?
> > For example: D6629 "x86: Emit LAHF/SAHF instead of PUSHF/POPF" [2]?
> 
> LAHF and SAHF come with the following note:
> 
> This instruction executes as described above in compatibility mode and legacy mode.
> It is valid in 64-bit mode only if CPUID.80000001H:ECX.LAHF-SAHF[bit 0] = 1.
> 
> So I suspect they can't be used.

Of course, there are other ways to save a single flag value (such as
setz).  It's up to the compiler developers to decide what they think is
best.

Alan Stern