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

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Date:   Tue, 9 Jun 2020 11:56:26 -0700
From:   Matt Helsley <mhelsley@...are.com>
To:     Steven Rostedt <rostedt@...dmis.org>
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, Jun 09, 2020 at 02:52:07PM -0400, Steven Rostedt wrote:
> 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.

I think I can so I'll give it a go!

Cheers,
	-Matt Helsley