linux-kernel - Re: [PATCH] Clarify CONFIG_DEBUG

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Message-ID: <20140204090809.GA19156@gmail.com>
Date:	Tue, 4 Feb 2014 10:08:25 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
	Richard Weinberger <richard@....at>,
	Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH] Clarify CONFIG_DEBUG_INFO's bloaty nature


* David Rientjes <rientjes@...gle.com> wrote:

> On Mon, 3 Feb 2014, Andrew Morton wrote:
> 
> > > > How do you define "huge bloat" if the size of vmlinux doesn't increase?
> > > 
> > > Don't be silly. The size of all the object files increase *hugely*.
> > 
> > yup, I disable this in my allmodconfig testing, to great effect.
> > 
> > That being said, I do think the text should make clear that the bloat
> > is a compile-time impact and not a runtime one.  Something like
> > 
> > --- a/lib/Kconfig.debug~lib-kconfigdebug-clarify-config_debug_infos-bloaty-nature-fix
> > +++ a/lib/Kconfig.debug
> > @@ -128,9 +128,9 @@ config DEBUG_INFO
> >  	  tools like crash, kgdb, LKCD, gdb, etc on the kernel.
> >  
> >  	  If you only want to have resolved symbols in kernel traces and
> > -	  are not going to need support for those tools above, you don't need
> > -	  to enable this as it is a huge bloat and build slowdown;
> > -	  enable CONFIG_KALLSYMS instead.
> > +	  are not going to need support for the above tools, you don't need
> > +	  to enable this.  It hugely bloat object files' on-disk sizes and slows
> > +	  the build.  Enable CONFIG_KALLSYMS instead.
> >  
> >  	  If unsure, say N.
> >  
> 
> Um, I still don't think this is right since 
> CONFIG_DEBUG_INFO_REDUCED requires you to say yes here and that 
> config option actually specifies the tools for which it is 
> effective.  Are you suggesting that we decouple CONFIG_DEBUG_INFO 
> from CONFIG_DEBUG_INFO_REDUCED and make CONFIG_DEBUG_INFO select the 
> reduced variant?  Or... what?

I think the right solution is what I suggested in another recent 
discussion:

"So to reign in debuginfo in allyesconfig/allmodconfig builds we could 
 do something like:

 config SAVE_TIME_AND_DISK_SPACE
        bool "Faster and leaner build object files: compile without debug info"
        default y

 choice
        prompt "Choose DEBUGINFO bloat level"
        depends on !SAVE_TIME_AND_DISK_SPACE
        default DEBUG_INFO_REDUCED
        help
           This option allows to select the debuginfo model.

   config DEBUG_INFO_REDUCED
        bool "Reduced amount of debugging information, 4x regular .o size"

   config DEBUG_INFO
        bool "Full debuginfo, 10x regular .o size, 'planet killer' version"

 endchoice

 That would default to Y and would disable debuginfo by default."

Thanks,

	Ingo

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