linux-kernel - Re: [PATCH v3 4/5] x86/asm: Add asm macros for static keys/jump labels

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Date:	Fri, 13 Nov 2015 09:22:57 -0500 (EST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andy Lutomirski <luto@...nel.org>
cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Brian Gerst <brgerst@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v3 4/5] x86/asm: Add asm macros for static keys/jump
 labels



On Thu, 12 Nov 2015, Andy Lutomirski wrote:

> Unfortunately, we can only do this if HAVE_JUMP_LABEL.  In principle, we
> could do some serious surgery on the core jump label infrastructure
> to keep the patch infrastructure available on x86 on all builds, but
> that's probably not worth it.
> 
> Implementing the macros using a conditional branch as a fallback
> seems like a bad idea: we'd have to clobber flags.
> 
> This limitation can't cause silent failures -- trying to include
> asm/jump_label.h at all on a non-HAVE_JUMP_LABEL kernel will error
> out.  The macro's users are responsible for handling this issue
> themselves.
> 
> Signed-off-by: Andy Lutomirski <luto@...nel.org>

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
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