[PATCH 0/5] Relocatable 64-bit kernel using linker PIE support

[David Miller]

From: Paul Mackerras <paulus at samba.org>
Date: Fri, 29 Aug 2008 15:40:36 +1000

> The main remaining substantial technical issue is how we detect very
> early on that we are a kdump kernel.  I think the policy should be
> that the kernel copies itself down to 0 if it's not a kdump kernel and
> runs wherever it was loaded if it's a kdump kernel.  The only way to
> tell whether we're a kdump kernel seems to be to look at the kernel
> command line, which is a little tricky to do in head_64.S when the
> command line is buried inside the DTB.

Why not put a key at a fixed location in the .text section or similar?
Then you can access it using PC relative addressing, and whatever
loads the kdump kernel can put an appropriate value there.