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

[Andrew Morton]

On Tue, 28 Feb 2012 09:40:57 +0000
Will Deacon <will.deacon at arm.com> wrote:

> > > Still, you didn't answer my question!  What effect will the absence of
> > > SYMBOL(swapper_pg_dir)= have upon downstream tools?  If "none" then
> > > sure, let's remove it.  If "explosion" then we should emit a dummy
> > > SYMBOL(swapper_pg_dir)=0 if CONFIG_NOMMU.
> > 
> > My thought was that the tools wouldn't be used in the CONFIG_NOMMU case (yet).
> > But I take your point and I think the answer is that the fallout is unknown.
> > Emitting a dummy value as you suggest seems reasonable.
> 
> The reason I didn't choose a dummy value to start with is because there are
> plenty of other fields in the dump that are predicated on build-time CONFIG
> options. Admittedly, some of these appear to be tagged with length
> information, but consider these guys:
> 
> #ifndef CONFIG_NEED_MULTIPLE_NODES
>         VMCOREINFO_SYMBOL(mem_map);
>         VMCOREINFO_SYMBOL(contig_page_data);
> #endif
> 
> Since the VMCOREINFO_SYMBOL macro stringifies the identifier, I guess userspace
> has to treat the whole thing as a map, meaning that we *can* safely remove
> elements from it.
> 
> So that's my speculation. Maybe somebody on the kexec list can confirm?

Yeah, I do think the chance of breaking anything here is small, and in
the unlikely event that something *does* break then a) it deserved to
break ;) and b) the user of that app will be a developer who can
unbreak it.

Let's run with the patch as-is.