linux-kernel - Re: [PATCH] perf: fix wrong DEBUG configuration

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Message-ID: <20150522070250.GA30715@gmail.com>
Date:	Fri, 22 May 2015 09:02:50 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Martin Liška <mliska@...e.cz>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] perf: fix wrong DEBUG configuration


* Arnaldo Carvalho de Melo <acme@...nel.org> wrote:

> Em Wed, May 20, 2015 at 06:16:51PM +0200, Martin Liška escreveu:
> > On 05/20/2015 04:55 PM, Ingo Molnar wrote:
> > >* Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> > >>So the rule has been: What are the kernel requirements for the
> > >>toolchain? tools/perf/ should build with that.
> > >
> > >So we could use -Og if it works, like Kbuild does it:
> > >
> > >         KBUILD_CFLAGS += $(call cc-option,-mno-fp-ret-in-387)
> > >
> > >the 'cc-option' Make function does some magic of silently calling GCC
> > >with that option and observing the result.
> 
> > >See:
> 
> > >   scripts/Kbuild.include:cc-option = $(call try-run,\
> 
> > I am sorry, I did mistake in understanding of DEBUG variable.
> > Following patch should be fixed, except missing auto-detection
> > of -Og option.
> > 
> > Unfortunately, following hunk does not work, no -Ox is added to CFLAGS?
> > 
> > --  CFLAGS += -Og
> > ++  CFLAGS += $(call cc-option,-Og,-O0)
> 
> I don't know if we have this cc-option, perhaps Ingo is suggesting 
> we get it in tools/build/? Or include scripts/Kbuild.include and 
> then use it?
> 
> I.e. we have checks to see if we can use, for instance 
> -fstack-protector-all, see tools/build/feature/Makefile, using this 
> cc-option thing, importing it from Kbuild would solve the issue at 
> hand in a definitive way and in line with what we have been 
> pursuing: to make the tools/ build system be based on Kbuild.

So I'd suggest copying any necessary functions instead of outright 
including all of Kbuild in the tooling build system which creates 
non-trivial dependencies that is not necessarily tested as thoroughly 
on the kbuild side as on the tooling side.

Thanks,

	Ingo
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