[Crash-utility] Re: crash-4.0-4.3 and linux-2.6.22.1-20.fc7

[Dave Anderson]

Bernhard Walle wrote:
> * Andi Kleen <andi at firstfloor.org> [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