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Re: [PATCH v7 04/10] ppc64 ftrace_with_regs configuration variables

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On Mon, Feb 08, 2016 at 10:49:28AM -0500, Steven Rostedt wrote:
> On Mon, 8 Feb 2016 16:23:06 +0100
> Petr Mladek <pmladek@suse.com> wrote:
> 
> > >From 2b0fcb678d7720d03f9c9f233b61ed9ed4d420b3 Mon Sep 17 00:00:00 2001  
> > From: Petr Mladek <pmladek@suse.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

Yes, I wrote a test to detect it at build time. It is similar to "asm goto"
and part of the v7 patch set.

> 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.

Please clarify. All I could find is Makefile magic that does it. AFAICS
This runs _after_ Kconfig.

But what I'd like to see is to offer the user the full choice, where possible,
e.g.

Kernel Tracing ...
0) none
1) static FTRACE
2) DYNAMIC_FTRACE
3) DYNAMIC_FTRACE_WITH_REGS

Can such a test be used to simply reduce these options?
With Petr's patch, it comes quite close to the above, and if you select "3"
and your compiler is broken, compilation will fail. For "2", it will just do
the right thing ( fall back to plain "-pg" ).

Without Petr's patch you have *no* choice between "2" and "3".
(That's what I'd call a bug :)

So, the question is, can such a test be used to provide _input_ to
"make config" ? I can see the "env=" mechanism, but it seems not to be used
very heavily. That would then be a prerequisite to all "make *config".
Even if it can provide this input, you can still not choose between 2 and 3
where both are available.

	Torsten

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[PATCH v7 00/10] ftrace with regs + live patching for ppc64 LE (ABI v2) Torsten Duwe <duwe@lst.de> - 2016-02-04 17:20 +0100
  [PATCH v7 03/10] ppc use ftrace_modify_all_code default Torsten Duwe <duwe@lst.de> - 2016-02-04 17:30 +0100
  [PATCH v7 02/10] ppc64le FTRACE_WITH_REGS implementation Torsten Duwe <duwe@lst.de> - 2016-02-04 17:30 +0100
  [PATCH v7 08/10] Implement kernel live patching for ppc64le (ABIv2) Torsten Duwe <duwe@lst.de> - 2016-02-04 17:30 +0100
  [PATCH v7 06/10] ppc64 ftrace: disable profiling for some functions Torsten Duwe <duwe@lst.de> - 2016-02-04 17:30 +0100
    Re: [PATCH v7 06/10] ppc64 ftrace: disable profiling for some  functions Michael Ellerman <mpe@ellerman.id.au> - 2016-02-10 03:00 +0100
      Re: [PATCH v7 06/10] ppc64 ftrace: disable profiling for some  functions Torsten Duwe <duwe@lst.de> - 2016-02-10 19:10 +0100
  [PATCH v7 04/10] ppc64 ftrace_with_regs configuration variables Torsten Duwe <duwe@lst.de> - 2016-02-04 17:30 +0100
    Re: [PATCH v7 04/10] ppc64 ftrace_with_regs configuration variables Petr Mladek <pmladek@suse.com> - 2016-02-05 15:10 +0100
      Re: [PATCH v7 04/10] ppc64 ftrace_with_regs configuration variables Steven Rostedt <rostedt@goodmis.org> - 2016-02-05 15:50 +0100
        Re: [PATCH v7 04/10] ppc64 ftrace_with_regs configuration variables Petr Mladek <pmladek@suse.com> - 2016-02-05 17:20 +0100
          Re: [PATCH v7 04/10] ppc64 ftrace_with_regs configuration variables Steven Rostedt <rostedt@goodmis.org> - 2016-02-05 17:40 +0100
          Re: [PATCH v7 04/10] ppc64 ftrace_with_regs configuration variables Torsten Duwe <duwe@lst.de> - 2016-02-06 11:40 +0100
            Re: [PATCH v7 04/10] ppc64 ftrace_with_regs configuration variables Petr Mladek <pmladek@suse.com> - 2016-02-08 11:40 +0100
              Re: [PATCH v7 04/10] ppc64 ftrace_with_regs configuration variables Torsten Duwe <duwe@lst.de> - 2016-02-08 13:20 +0100
                Re: [PATCH v7 04/10] ppc64 ftrace_with_regs configuration variables Petr Mladek <pmladek@suse.com> - 2016-02-08 16:30 +0100
                Re: [PATCH v7 04/10] ppc64 ftrace_with_regs configuration variables Steven Rostedt <rostedt@goodmis.org> - 2016-02-08 16:50 +0100
                Re: [PATCH v7 04/10] ppc64 ftrace_with_regs configuration variables Petr Mladek <pmladek@suse.com> - 2016-02-08 17:40 +0100
                Re: [PATCH v7 04/10] ppc64 ftrace_with_regs configuration variables Torsten Duwe <duwe@lst.de> - 2016-02-09 10:10 +0100
  [PATCH v7 10/10] livepatch: Detect offset for the ftrace location  during build Petr Mladek <pmladek@suse.com> - 2016-02-04 17:30 +0100
  [PATCH v7 07/10] ppc64 ftrace: disable profiling for some files Torsten Duwe <duwe@lst.de> - 2016-02-04 17:30 +0100
    Re: [PATCH v7 07/10] ppc64 ftrace: disable profiling for some files Michael Ellerman <mpe@ellerman.id.au> - 2016-02-10 01:40 +0100
      Re: [PATCH v7 07/10] ppc64 ftrace: disable profiling for some files Torsten Duwe <duwe@lst.de> - 2016-02-10 19:00 +0100
  [PATCH v7 01/10] ppc64 (le): prepare for -mprofile-kernel Torsten Duwe <duwe@lst.de> - 2016-02-04 17:30 +0100
  [PATCH v7 09/10] Enable LIVEPATCH to be configured on ppc64le and add  livepatch.o if it is selected. Torsten Duwe <duwe@lst.de> - 2016-02-04 17:30 +0100
  [PATCH v7 05/10] ppc64 ftrace_with_regs: spare early boot and low  level Torsten Duwe <duwe@lst.de> - 2016-02-04 17:30 +0100

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