Re: Re: crash-4.0-4.3 and linux-2.6.22.1-20.fc7

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Bernhard Walle wrote:
* Andi Kleen <andi@xxxxxxxxxxxxxx> [2007-07-23 12:26]:

What might have changed when you enable the relocatable kernel
is that the ELF addresses in the vmlinux are different. But
at runtime there is no difference.


But that change only broke GDB (> 6.5) and not crash (which is based
on GDB 6.1). See http://sourceware.org/ml/gdb/2007-06/msg00020.html.


Thanks,
   Bernhard

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I've got this private email from Vivek, which I'll un-privatize here,
that might explain the issue:

Hi Dave,

Sorry, could not reply on Friday.

This looks weared. Only one possible theory comes to mind. In FC7 kernels
following should be config variables.

CONFIG_PHYSICAL_START=16MB
CONFIG_PHYSICAL_ALIGN=4MB.

That means kernel has been compiled for 16MB physical address. That's
why linux_banner symbol address is in higher range. But at run time it
has been loaded by grub at 1MB location. Because alignment required is
4MB kernel will move itself to physical address 4MB and that would
probably put linux banner somewhere at 6MB location.

So these kind of problems will occur with first kernel is not run at
the address it has been compiled for. Can you please confirm this by
looking at FC7 config file.

An easy way to fix this would be to change CONFIG_PHYSICAL_START=1MB.

Thanks
Vivek

Thanks Vivek.

My FC7 kernel does have:

CONFIG_PHYSICAL_START=0x1000000  (16MB)
CONFIG_PHYSICAL_ALIGN=0x400000   (4MB)

I'm just about to build a kernel with CONFIG_PHYSICAL_START
set back to 1MB to see what happens.

FWIW, RHEL5 kernels don't use CONFIG_PHYSICAL_START (except
for the defunct "kdump" kernel), but have CONFIG_PHYSICAL_ALIGN
set to 4MB.

Thanks,
  Dave










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