Re: Linux 4.3 kallsyms_lookup_name not returning per_cpu symbol values

[Jeffrey Merkey]

I tracked this down and it turns out to be a page mapping problem with
one of the sound drivers on the system trashing memory.   It's a bug,
but a bug in a vendor supplied driver.

Jeff

On 11/18/15, Jeffrey Merkey <jeffmerkey@xxxxxxxxx> wrote:
> kallsyms_lookup_name is not returning per_cpu symbols when called.
> The symbols show up when you run something with the kallsyms_iter
> struct but not through the regular interface.  I have looked through
> the code and I am not able to determine with certainty if its designed
> this way or just busted.  Any help with this would be appreciated.
>
> The following code does display the per_cpu symbols, they just don't
> seem to show up when called from kallsyms_lookup_name.
>
>
> struct kallsym_iter mdb_iter;
> int mdb_kallsyms(char *str, int (*print)(char *s, ...))
> {
>     register loff_t pos = 0;
>     register struct kallsym_iter *iter = &mdb_iter;
>
>     if (!print)
>        return 0;
>
>     // set to beginning of the kallsyms list
>     reset_iter(iter, 0);
>     while (1)
>     {
>        // search the kallsyms list
>        if (!update_iter(iter, pos++))
>           break;
>
>        if (!iter->name[0])
> 	  continue;
>
>        // if an exclusion search was specified, skip non-matching entries
>        if (str && *str && !strstr(iter->name, str))
>           continue;
>
>        if (iter->module_name[0])
>        {
>           if (print("%0*lx %c %s [%s]\n", (int)(2*sizeof(void*)),
> 	      iter->value, iter->type, iter->name,
> 	      iter->module_name))
>              return 1;
>        }
>        else
>        {
>           if (print("%0*lx %c %s\n", (int)(2*sizeof(void*)),
> 	      iter->value, iter->type, iter->name))
>              return 1;
>        }
>     }
>     return 0;
> }
> EXPORT_SYMBOL_GPL(mdb_kallsyms);
>
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