Re: kexec fails to boot kernels where CONFIG_RANDOMIZE_BASE=y is set

[Vivek Goyal <vgoyal@redhat.com>]

On Fri, Aug 22, 2014 at 07:59:02PM +0800, Baoquan He wrote:

[..]
> So we have 2 choices for kexec/kdump:
> 1) kexec/kdump kernel need not randomize the kernel starting point.
> Since kexec/kdump kernel is only for testing or emergencey, its life is
> not too long.
> 
> 2) makes slots around the kernel input addr. This is only useful for
> kexec. I can't imagine why kdump need it. 
> 
> 
> 
> 
> Hi Thomas,
> Could you test below patch? 
> 
> 
> This is patch is from Lu Yinghai.
> ---
>  arch/x86/boot/compressed/misc.c |   14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> Index: linux-2.6/arch/x86/boot/compressed/misc.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/boot/compressed/misc.c
> +++ linux-2.6/arch/x86/boot/compressed/misc.c
> @@ -235,8 +235,9 @@ static void error(char *x)
>  		asm("hlt");
>  }
>  
> -#if CONFIG_X86_NEED_RELOCS
> -static void handle_relocations(void *output, unsigned long output_len)
> +#ifdef CONFIG_X86_NEED_RELOCS
> +static void handle_relocations(void *output_orig, void *output,
> +			       unsigned long output_len)
>  {
>  	int *reloc;
>  	unsigned long delta, map, ptr;
> @@ -247,7 +248,7 @@ static void handle_relocations(void *out
>  	 * Calculate the delta between where vmlinux was linked to load
>  	 * and where it was actually loaded.
>  	 */
> -	delta = min_addr - LOAD_PHYSICAL_ADDR;
> +	delta = min_addr - (unsigned long)output_orig;

So what does this patch actuall do? If I try to trace back output_orig,
it seems to be same as LOAD_PHYSICAL_ADDR. That means there should not
be any effect of this change? Or did I not understand it.

Look at head_64.S

movq    $LOAD_PHYSICAL_ADDR, %rbp
...
...
movq    %rbp, %r8               /* output target address */
call    decompress_kernel       /* returns kernel location in %rax */

Thanks
Vivek

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