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

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Date:	Sun, 20 Jul 2014 14:17:30 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kbuild@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] Kbuild: Add a option to enable dwarf4

On Sun, Jul 20, 2014 at 09:23:15PM +0200, Sam Ravnborg wrote:
> 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.

I made it a separate option, because dwarf4 is somewhat bigger than dwarf3 and it's
probably only useful for people actively using gdb/crash
(and I don't think others users like systemtap/perf probe do dwarf4 yet)

If debug fusion was default it would be fine, but right now it would
need converting a lot of debuginfo packaing scripts first.

-Andi
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