linux-kernel - Re: [PATCHv3 2/3] kernel: add support for live patching

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Message-ID: <20141121153535.GC26264@treble.redhat.com>
Date:	Fri, 21 Nov 2014 09:35:35 -0600
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Seth Jennings <sjenning@...hat.com>,
	Vojtech Pavlik <vojtech@...e.cz>,
	Steven Rostedt <rostedt@...dmis.org>,
	Petr Mladek <pmladek@...e.cz>, Miroslav Benes <mbenes@...e.cz>,
	Christoph Hellwig <hch@...radead.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	live-patching@...r.kernel.org, x86@...nel.org, kpatch@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 2/3] kernel: add support for live patching

On Fri, Nov 21, 2014 at 04:27:57PM +0100, Jiri Kosina wrote:
> On Fri, 21 Nov 2014, Josh Poimboeuf wrote:
> 
> > I think we can use "depends on HAVE_FENTRY" to accomplish this, since 
> > CC_USING_FENTRY gets set by the top level kernel Makefile if 
> > CONFIG_HAVE_FENTRY is set.
> 
> The problem is that HAVE_FENTRY is set automatically on x86_64, no matter 
> whether your actual compiler supports it or not.
> 
> CC_USING_FENTRY is defined if and only if the actual currently used 
> compiler supports it, but that can't be expressed in Kconfig.

Ah, light bulb moment.  Now I understand what "$(call cc-option, ...)"
does.

Thanks :-)

-- 
Josh
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