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

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Message-ID: <555CB373.7090007@suse.cz>
Date:	Wed, 20 May 2015 18:16:51 +0200
From:	Martin Liška <mliska@...e.cz>
To:	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>
CC:	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

On 05/20/2015 04:55 PM, Ingo Molnar wrote:
>
> * Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
>
>> Em Wed, May 20, 2015 at 03:29:37PM +0200, Martin Liška escreveu:
>>> On 05/20/2015 03:17 PM, Arnaldo Carvalho de Melo wrote:
>>>> Em Wed, May 20, 2015 at 03:07:39PM +0200, Martin Liška escreveu:
>>>>> Currently, GCC optimizes -O6 same as -O3 level. Right optimize debugging
>>>>> experience is given by passing -Og to compiler.
>>
>>>> Is this is this -Og available in old gcc versions? When was it
>>>> introduced? Do you know?
>>
>>> GCC 4.8.0 is the first version capable of the option: https://gcc.gnu.org/gcc-4.8/changes.html.
>>> That can be problematic, which GCC version do you support in linux/perf?
>>
>> 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,\
>
> et al.
>
> Thanks,
>
> 	Ingo
>

Hi.

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)


Thanks,
Martin

View attachment "perf-fix-wrong-DEBUG-configuration-v3.patch" of type "text/x-patch" (2233 bytes)