[Crash-utility] [PATCH/RFC] Fix relocation address

[Dave Anderson]

----- "Simon Kagstrom" <simon.kagstrom at netinsight.net> wrote:

> On Thu, 17 Dec 2009 11:17:56 -0500 (EST)
> Dave Anderson <anderson at redhat.com> wrote:
> 
> > > > So I started looking into the code and found something which looks like
> > > > a typo in relocate() (patch below). Changing this makes crash work for me.
> > > 
> > > Actually it's not a typo -- your patch would presumably break with all kernels
> > > that have a CONFIG_PHYSICAL_START is greater than CONFIG_PHYSICAL_ALIGN, which
> > > is what the patch was written to handle.
> > > 
> > > What are your kernel's CONFIG_PHYSICAL_START and CONFIG_PHYSICAL_ALIGN
> > > values?  Does crash work with your kernel on the live system?  
> 
> You are right. I had problems with getting things working, so I've
> played around with various settings. I had CONFIG_PHYSICAL_START set to
> 0 and CONFIG_PHYSICAL_ALIGN set to 0x100000. Setting these to e.g.,
> 0x100000 and 0x100000 unbreaks things again.
> 
> I don't need to supply --reloc either then, not sure what I did wrong
> before. I'm sticking with sane settings from now on.
> 
> > > Anyway, I believe that the fix would require support for supplying a 
> > > negative --reloc value.
> > 
> > On the other hand, if the config values were the other way around, the 
> > problem didn't use to show up -- at least according to list item "1)"
> > below in the changelog:
> > 
> >             1) Configure the kernel with CONFIG_PHYSICAL_START less than
> >                or equal to CONFIG_PHYSICAL_ALIGN.  Having done that, there
> >                is no problem; the resultant vmlinux file will be loaded at
> >                the address for which it was compiled, which has always
> >                been the case.
> 
> > I wonder if you can use the unpatched crash, but supply a --reloc value that
> > will cause a wrap-around to the correct value?
> 
> Well, I suppose that would work if it was possible to supply a negative
> --reloc value, but I'm not sure it's really worth it. What would be
> nice would be to get a more descriptive error message.

Yeah, the problem is that the "do not match" errors can result from
a multitude of error scenarios.  Usually by entering a "-d <number>"
on the command line (the higher the debug number the more verbose),
the issue generating the failure typically is evident.

> 
> Thanks for the help, please ignore the patch.

OK for now -- and thanks for posting.  It's only a matter of time before
somebody else runs into the same thing.

Thanks,
  Dave

> 
> // Simon