[PATCH] kexec: crash: don't save swapper_pg_dir for !CONFIG_MMU configurations

[Simon Horman]

On Mon, Feb 27, 2012 at 04:26:31PM -0800, Andrew Morton wrote:
> On Tue, 28 Feb 2012 09:19:28 +0900
> Simon Horman <horms at verge.net.au> wrote:
> 
> > > > --- a/kernel/kexec.c
> > > > +++ b/kernel/kexec.c
> > > > @@ -1462,7 +1462,9 @@ static int __init crash_save_vmcoreinfo_init(void)
> > > >  
> > > >  	VMCOREINFO_SYMBOL(init_uts_ns);
> > > >  	VMCOREINFO_SYMBOL(node_online_map);
> > > > +#ifdef CONFIG_MMU
> > > >  	VMCOREINFO_SYMBOL(swapper_pg_dir);
> > > > +#endif
> > > >  	VMCOREINFO_SYMBOL(_stext);
> > > >  	VMCOREINFO_SYMBOL(vmlist);
> > > 
> > > Well, what might be the effects of this patch?  nommu crashfiles will
> > > no longer have the swapper_pg_dir string?  What are the chances that
> > > someone's (badly written!) downstream tool will crash and burn if this
> > > is absent?
> > 
> > My understanding is that up until this patch creating a dump
> > for nonmmu platform wouldn't work.
> 
> Surprised.  From reading the code I expect it would have emitted 
> 
> 	SYMBOL(swapper_pg_dir)=0

Hi Andrew,

My understanding from discussion with Will earlier in this thread is that if
CONFIG_MMU is not defined then swapper_pg_dir is NULL and the current code
doesn't compile.

	<quote>
	The only case where it's interesting is when you have CONFIG_MMU
	enabled - otherwise it's always NULL. If it's #defined as NULL, the
	current code will fail at build time so simply omitting it from the
	dump seems like the best bet to me (the alternative being to add a
	NULL entry explicitly, but I don't see what the gains us).
	</quote>