Re: [PATCH] Add the symbol "phys_base" to vmcoreinfo

[Vivek Goyal <vgoyal@redhat.com>]

On Mon, Mar 31, 2008 at 08:00:25PM +0900, Ken'ichi Ohmichi wrote:
> 
> Hi Andrew,
> 
> This patch fixes the problem that makedumpfile sometimes fails
> on x86_64 machine. I hope that this patch will be merged to both
> linux-2.6.25 and linux-2.6.24.5.
> 
> This patch adds the symbol "phys_base" to a vmcoreinfo data.
> The vmcoreinfo data has the minimum debugging information only
> for dump filtering. makedumpfile (dump filtering command) gets
> it to distinguish unnecessary pages, and makedumpfile creates
> a small dumpfile.
> 
> On x86_64 kernel which compiled with CONFIG_PHYSICAL_START=0x0
> and CONFIG_RELOCATABLE=y, makedumpfile fails like the following:
> 
>  # makedumpfile -d31 /proc/vmcore dumpfile
>  The kernel version is not supported.
>  The created dumpfile may be incomplete.
>  _exclude_free_page: Can't get next online node.
> 
>  makedumpfile Failed.
>  #
> 
> The cause is the lack of the symbol "phys_base" in a vmcoreinfo
> data. If the symbol "phys_base" does not exist, makedumpfile
> considers an x86_64 kernel as non relocatable. As the result,
> makedumpfile misunderstands the physical address where the kernel
> is loaded, and it cannot translate a kernel virtual address to
> physical address correctly. To fix this proble, the attached
> patch which adds the symbol "phys_base" to a vmcoreinfo data.
> 
> 
> Thanks
> Ken'ichi Ohmichi
> 
> 
> Signed-off-by: Ken'ichi Ohmichi <oomichi@mxs.nes.nec.co.jp>
> ---
> diff -rpuN linux-2.6.25-rc7.orig/arch/x86/kernel/machine_kexec_64.c linux-2.6.25-rc7/arch/x86/kernel/machine_kexec_64.c
> --- linux-2.6.25-rc7.orig/arch/x86/kernel/machine_kexec_64.c	2008-03-26 14:55:29.000000000 +0900
> +++ linux-2.6.25-rc7/arch/x86/kernel/machine_kexec_64.c	2008-03-26 14:52:52.000000000 +0900
> @@ -233,6 +233,7 @@ NORET_TYPE void machine_kexec(struct kim
>  
>  void arch_crash_save_vmcoreinfo(void)
>  {
> +	VMCOREINFO_SYMBOL(phys_base);
>  	VMCOREINFO_SYMBOL(init_level4_pgt);

CCing to LKML.

Looks good to me. Given a vmcore file, one needs to know about
the shift between compile address and run time address of kernel
to be able to do filtering. This shift (phys_base) will vary
based on kernel config options and based on where boot loader
has loaded a kernel.

Acked-by: Vivek Goyal <vgoyal@redhat.com>

Thanks
Vivek

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