On Thu, 2006-02-23 at 15:26 -0500, Dave Jones wrote:
> On Thu, Feb 23, 2006 at 09:13:24PM +0100, Rene Herman wrote:
> > Linus Torvalds wrote:
> >
> > >If you want to boot a 4MB machine with the suggested patch, you'd
> > >have to enable CONFIG_EMBEDDED (something you'd likely want to do
> > >anyway, for 4M machine), and turn the physical start address back
> > >down to 1MB.
> >
> > Okay. I suppose the only other option is to make "physical_start" a
> > variable passed in by the bootloader so that it could make a runtime
> > decision? Ie, place us at min(top_of_mem, 4G) if it cared to. I just
> > grepped for PHYSICAL_START and this didn't look _too_ bad.
> >
> > I'm out of my league here though -- if I remember correctly from some
> > reading of the early bootcode I once did, the kernel set up some
> > temporary tables first to only cover the first few MB? If so, then I
> > guess it would be a significant change.
> >
> > Seems a bit cleaner though than just hardcoding the address.
>
> the kdump people were looking at making the kernel runtime relocatable
> at one point, which with my distro-vendor hat on, would be useful
> as it'd mean we could use the same kernel image for normal boot, and
> also for the 'kdump kernel'
The mkdump team has accomplished this ...
> (Right now, we ship another set of
> kernels for each arch with a different PHYSICAL_START).
... so that we do not need to hard-code PHYSICAL_START. The dump capture
kernel is able to run from any memory address the host kernel reserves
for it. The are some limitations though:
- i386: the second kernel has to be loaded in low memory
- x86_64: the second kernel has to be loaded below 1GB (we are working
to move this limit to 4GB)
> (You wouldn't believe how much grief we get from the installer folks
> for adding another set of kernel images to the ISOs).
>
> I think that work stalled a while back though.
The mkdump team has been using runtime relocatable kernels for two years
and we are currently working on porting this functionality to kdump. I
was wondering if it would be accepted mainstream.
Regards,
Fernando
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