linux-kernel - Re: [RFC PATCH 3/4] ftrace: Do not test frame pointers if -mfentry is used

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Date:	Wed, 08 Aug 2012 23:57:38 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Michal Marek <mmarek@...e.cz>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [RFC PATCH 3/4] ftrace: Do not test frame pointers if -mfentry
 is used

On Thu, 2012-08-09 at 06:45 +0300, Linus Torvalds wrote:
> On Wed, Aug 8, 2012 at 3:49 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> >
> > No, CONFIG_HAVE_FENTRY just means fentry is supported, it does not mean
> > that it is being used. It only gets used if CC_USING_FENTRY is set,
> > which is set by the Makefile at time of compile.
> 
> Btw, it might be lovely to consider the concept of "Kconfig variables
> set by shell-scripts".
> 
> We currently have a metric sh*t-ton of Makefile magic for testing
> various things like this, and integrating it into Kconfig might be a
> good idea. That way you would be able to use the Kconfig logic on
> these things.
> 
> Kconfig already has the "option env=XYZ" syntax for importing values
> from the environment variables. Extending it to some kind of "option
> shell=xyz" would allow for more complex interactions like this
> (imagine testing compiler options and version dependencies in the
> Kconfig files instead of the Makefiles)?

I understand your pain. I think this 'test the environment in the
makefile' is a bit of a hack.

I've worked a little with the Kconfig infrastructure, but I wouldn't
consider myself an expert. Would Kconfig be able to handle a change in
environment? That is, if you change your compiler, would a normal make
kick off Kconfig to update the configs for the new environment. Or would
the user have to do some kind of 'make oldconfig' before that.

Or is make 'oldconfig' performed at all compiles regardless now?

One nice thing of having all these tests represented in the .config
file, is that when a user produces a bug, when they send their config,
we would be able to see much more information about their environment.

-- Steve


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