linux-kernel - Re: [RFC][PATCH v4 02/32] objtool: Make recordmcount into mcount subcmd

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Message-ID: <20200609145207.1d9dafa2@oasis.local.home>
Date:   Tue, 9 Jun 2020 14:52:07 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Matt Helsley <mhelsley@...are.com>
Cc:     Julien Thierry <jthierry@...hat.com>,
        <linux-kernel@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>
Subject: Re: [RFC][PATCH v4 02/32] objtool: Make recordmcount into mcount
 subcmd

On Tue, 9 Jun 2020 11:39:51 -0700
Matt Helsley <mhelsley@...are.com> wrote:

> > > +ifeq ($(SRCARCH),sparc)
> > > +	SUBCMD_MCOUNT := y  
> > 
> > Is there some arch for which MCOUNT is not supported? If not you could just
> > have MCOUNT default to 'y' and avoid adding all those tests (or maybe reduce
> > the numbers and set to 'n' only for arches not supporting it).  
> 
> Yes, there are some which it does not support. For those architectures
> we keep recordmcount.pl around.
> 
> It occured to me that with your suggestion to use more CONFIG_ variables
> we could eliminate this pattern and replace it with these pseudo-patches:
> 
> +++ b/kernel/trace/Kconfig
> 
> +config OBJTOOL_SUBCMD_MCOUNT
> +	bool
> +	depends on HAVE_C_RECORDMCOUNT
> +	select OBJTOOL_SUBCMDS
> +	help
> +	  Record mcount call locations using objtool
> 
> and then change the Makefiles to use the CONFIG_ variables
> rather than have one ifeq block per arch:
> 
> +++ b/tools/objtool/Makefile
> 
> +SUBCMD_MCOUNT := $(CONFIG_OBJTOOL_SUBCMD_MCOUNT)

If you can make this work, this is definitely the way to go.

-- Steve

> 
> Does this seem like a good use of CONFIG_ variables or is it going too
> far?
> 
> I haven't changed to this pattern just yet -- I'm hoping you and Josh
> or Peter might weigh in with your preferences.