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?
Neil
> P.
>
> > Thanks,
> >
> > Jiri
> >
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