linux-kernel - Re: [PATCH 2/2] Kbuild: Add a option to enable dwarf4

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Message-ID: <20140720192315.GA4679@ravnborg.org>
Date:	Sun, 20 Jul 2014 21:23:15 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 2/2] Kbuild: Add a option to enable dwarf4

On Wed, Jul 16, 2014 at 01:16:12AM +0200, Andi Kleen wrote:
> From: Andi Kleen <ak@...ux.intel.com>
> 
> I found that a lot of unresolvable variables when using gdb on the kernel
> become resolvable when dwarf4 is enabled. So add a Kconfig flag to enable it.
> 
> It definitely increases the debug information size, but on the other
> hand this isn't so bad when debug fusion is used.

Would it not make sense to try to enable degug info like this:
First try -gdwarf-4
If this fails try -gdwarf-3
If this fails try -gdwarf-2
And if this also fails fallback to -g

We could then us a Kconfig option to enable the highest debug level - where 4 for now is the highest.
On the other hand if most people have revent utils then they all have -gdwarf-4 supported
and then it is no big deal.

	Sam

> 
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> ---
>  Makefile          | 3 +++
>  lib/Kconfig.debug | 9 +++++++++
>  2 files changed, 12 insertions(+)
> 
> diff --git a/Makefile b/Makefile
> index 953659e..9c4080b 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -690,6 +690,9 @@ KBUILD_CFLAGS	+= -g
>  KBUILD_AFLAGS	+= -Wa,-gdwarf-2
>  endif
>  endif
> +ifdef CONFIG_DEBUG_INFO_DWARF4
> +KBUILD_CFLAGS	+= -gdwarf-4
> +endif
Should we sue $(call cc-option ...) here as not all gcc's supports this today?

	Sam
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