Subject: Re: [PATCH 3/3] powerpc/ppc64/kdump: better flag for running relocatable

From: Milton Miller <[email-masked]>
Date: Fri, 7 Nov 2008 07:52:31 -0600

On Oct 22, 2008, at 10:43 PM, Paul Mackerras wrote:
> Paul Mackerras writes:
>> Milton Miller writes:
>>> Move the flag to 0x5c, 1 word before the secondary cpu entry point at
>>> 0x60.  Use the copy at address 0 not the one in the base kernel 
>>> image to
>>> make it easier on kexec-tools.
>>
>> Why is it easier on kexec-tools?  Doesn't kexec-tools know where it
>> put the kernel?

The archictecture code calls cross-platform code to identify what is
loaded.   It isn't specified if this is a shared mmap or a read into
a buffer.

>>
>> I'd much rather keep the flag inside the kdump kernel image, rather
>> than having kexec/kdump start using random fixed locations outside the
>> new kernel image.
>
> In fact the cliching argument is that when the kernel is loaded by OF
> or yaboot, we have no way to tell what will be at location 0x5c,
> whereas we know that the word at offset 0x5c in the kernel image will
> have been initialized to 0.  So we had better put the flag inside the
> kernel image.

Well, prom_init will copy the 256 bytes to 0 before the code checks
that location.

However, there is an arguement for using the same code from an epapr
or book-e relocatable, and that would need it at 0.   And today
the kexec tool does not do a shared mmap.  Since the change has
been made, I will make a new patch for kexec-tools.

milton