Re: Linux 4.3 kallsyms_lookup_name not returning per_cpu symbol values

[Jeffrey Merkey]

Take that back, I just reproduced it again.  Seems to affect random
symbols not just per cpu.  I'll research some more.



On 11/18/15, Jeffrey Merkey <jeffmerkey@xxxxxxxxx> wrote:
> 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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