[Crash-utility] [Patch] linux-2.6.22 on i386

[Dave Anderson]

Ken'ichi Ohmichi wrote:
> Hi Dave,
> 
> I found the problem that the crash utility fails during the initialization.
> This problem happened on i386 linux-2.6.22 like the following:
> 
>   $ crash vmlinux vmcore
>   
>   crash 4.0-4.4
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>   
>   crash: invalid size request: 0  type: "__per_cpu_offset"
>   $ 
> 
> The cause is that the array number of the symbol "__per_cpu_offset"
> cannot be taken. In linux-2.6.21, i386's "__per_cpu_offset" is defined
> in include/asm-generic/percpu.h like the following:
> 
>   extern unsigned long __per_cpu_offset[NR_CPUS];
> 
> But in linux-2.6.22, it is defined in include/asm-i386/percpu.h like
> the following, and the array number is not described in the debugging
> information.
> 
>   extern unsigned long __per_cpu_offset[];
> 
> 
> Here is the patch for solving the problem. If the array number is not
> taken, the crash utility assumes that it is  the defined value NR_CPUS.
> Or, should get_array_length() be fixed to get the array number from
> init/main.c ?
> 

Ken'ichi -- thanks for tracking that down.

I don't see how get_array_length() can be "fixed" in this case -- if the
vmlinux file doesn't have the info, it doesn't have it.  I'm not sure
what you mean by getting it from init/main.c?

Anyway, using NR_CPUS is probably safe, although it runs the remote
risk of reading into a non-existent section of memory or uncopied
section of dumpfile.

How about using Cliff Wickman's new get_cpus_possible() function
from his LKCD_KERNTYPES patch?  Since get_cpus_possible() returns 0
on failure, your fix below should be left in place, but it might be
worth also trying get_cpus_possible() if get_array_length() returns 0?

Dave

> 
> Thanks
> Ken'ichi Ohmichi
> 
> --- crash-4.0-4.4.org/kernel.c	2007-07-21 04:19:23.000000000 +0900
> +++ crash-4.0-4.4/kernel.c	2007-07-24 19:51:55.000000000 +0900
> @@ -170,7 +170,7 @@ kernel_init()
>  		else
>  			i = get_array_length("__per_cpu_offset", NULL, 0);
>  		get_symbol_data("__per_cpu_offset",
> -			sizeof(long)*(i <= NR_CPUS ? i : NR_CPUS),
> +			sizeof(long)*((i && (i <= NR_CPUS)) ? i : NR_CPUS),
>  			&kt->__per_cpu_offset[0]);
>                  kt->flags |= PER_CPU_OFF;
>  	}
> _
> 
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