linux-kernel - Re: [PATCH v7 04/10] ppc64 ftrace_with

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Date:	Mon, 8 Feb 2016 17:32:26 +0100
From:	Petr Mladek <pmladek@...e.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Torsten Duwe <duwe@....de>, Michael Ellerman <mpe@...erman.id.au>,
	Jiri Kosina <jkosina@...e.cz>, Miroslav Benes <mbenes@...e.cz>,
	Jessica Yu <jeyu@...hat.com>, linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org, live-patching@...r.kernel.org
Subject: Re: [PATCH v7 04/10] ppc64 ftrace_with_regs configuration variables

On Mon 2016-02-08 10:49:28, Steven Rostedt wrote:
> On Mon, 8 Feb 2016 16:23:06 +0100
> Petr Mladek <pmladek@...e.com> wrote:
> 
> > >From 2b0fcb678d7720d03f9c9f233b61ed9ed4d420b3 Mon Sep 17 00:00:00 2001  
> > From: Petr Mladek <pmladek@...e.com>
> > Date: Mon, 8 Feb 2016 16:03:03 +0100
> > Subject: [PATCH] ftrace: Allow to explicitly disable the build of the dynamic
> >  ftrace with regs
> > 
> > This patch allows to explicitly disable
> > CONFIG_DYNAMIC_FTRACE_WITH_REGS. We will need to do so on
> > PPC with a broken gcc. This situation will be detected at
> > buildtime and could not be handled by Kbuild automatically.
> 
> Wait. Can it be detected at build time? That is, does it cause a build
> error? If so, then you can have Kbuild automatically detect this and
> set the proper value. We do this with 'asm goto'. There's tricks in the
> build system that can change the configs based on if a compiler is
> broken or not.

Just to be sure.

Do you suggest to define CONFIG_DYNAMIC_FTRACE_WITH_REGS
via a check in Makefile and rename it to e.g.
CC_FTRACE_WITH_REGS.

Or should we define another variable, e.g.
CC_BROKEN_DYNAMC_FTRACE_WITH_REGS? And then replace all occurences in
the code by something like:

-#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+#if defined(CONFIG_DYNAMIC_FTRACE_WITH_REGS) && \
+    !defined(CC_BROKEN_DYNAMC_FTRACE_WITH_REGS)

?

Best Regards,
Petr