makedumpfile: get_max_mapnr() from ELF header problem

[Michael Holzheu]

On Mon, 3 Mar 2014 03:11:23 +0000
Atsushi Kumagai <kumagai-atsushi at mxc.nes.nec.co.jp> wrote:

> Hello Michael,
> 
> >Hello Atsushi,
> >
> >On s390 we have the following little problem:
> >
> >We use hypervisor or stand-alone dump tools to create Linux system
> >dumps. These tools do not know the kernel parameter line and dump the
> >full physical memory.
> >
> >We use makedumpfile to filter those dumps.
> >
> >If a Linux system has specified the "mem=" parameter, the dump tools
> >still dump the whole phypsical memory.
> 
> I guess this is a problem of the tools, it sounds that the tools ignore
> the actual memory map and just make wrong ELF headers.
> How do the tools decide the range of System RAM to create ELF headers ?

The tools do a physical memory detection and that defines the range
of memory to be dumped and also defines the memory chunks for the
ELF header.

And I think we are not the only ones that have this problem. For example,
the KVM virsh dump probably also has that problem.

> 
> At least, if the tools respect the actual memory map like /proc/vmcore, it
> can create correct ELF headers and makedumpfile will work normally.

As I said, the tools do not know the Linux memory map. They only know
the physical available memory.

Michael