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Date: Mon, 7 Mar 2016 13:07:33 -0500 (EST)
From: Alan Stern <stern@rowland.harvard.edu>
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To: David Laight <David.Laight@ACULAB.COM>
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Subject: RE: [PATCH] usbhid: Fix lockdep unannotated irqs-off warning
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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