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

[Simon Kagstrom]

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.

Thanks for the help, please ignore the patch.

// Simon