On 5/21/20 9:37 AM, Neil Horman wrote:
> On Thu, May 21, 2020 at 09:27:35AM -0400, Prarit Bhargava wrote:
>> On 5/21/20 9:18 AM, Jiri Benc wrote:
>>> On Thu, 21 May 2020 08:31:56 -0400, Prarit Bhargava wrote:
>>>> We've used it (heavily might I add) to debug the kernel. It's a convenient
>>>> place for a quick kernel module.
>>>
>>> Now I'm curious. How does such module help debugging the kernel?
>>>
>>> I'm not saying you're wrong. I'm just saying I can't think of anything.
>>> Probably just me not being imaginative enough. More details would be
>>> appreciated. It might come handy one time.
>>>
>>
>> Well it's literally everything from dumping random values to confirming
>> alignment of structs to debugging.
>>
>> What I'm doing today is attempting to break the Intel Split Lock detector by
>> running
>>
>> for (cpu = 0; cpu < nr_cpu_ids; cpu++) {
>> c = &cpu_data(cpu);
>> printk("data for cpu %d\n", cpu);
>> for (i = 0; i < (NCAPINTS + NBUGINTS * 32); i++) {
>> cpu_has(c, i);
>> }
>> }
>>
>> in a tight loop. Unfortunately that doesn't seem to kick it. I suspect that
>> the cpuinfo_x86 struct is magically aligned atm :(.
>>
>> I guess I could keep the dummy-module in it's own tree but that's just a PITA
>> when I have to quickly debug something. Let's keep it in the tree where it's
>> always been ;)
>>
> I remember using this module quite alot, and it was very helpful. I have to
> ask
> though, does systemtap offer the same level of functionality at this point for
> most of the debugging we need to do?
>
Yup! But I have had many cases when I'm digging for HW register values, etc.,
that a module has been _invaluable_.
P.
> Neil
>
>> P.
>>
>>> Thanks,
>>>
>>> Jiri
>>>
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