"Core" thread doesn't become active in kernel initialization

[Stefan Kalkowski]

Hi Bob,

On 07/01/2015 09:42 PM, Bob Stewart wrote:
> Hi,
> 
>      I'm bringing up Genode (15.05) on an TI AM437x SoC and it is 
> failing kernel initialization. The initialization appears go ok until 
> the call to init_kernel_mp_primary(). Once the Core_thread singleton is 
> created the last printf output that appears is one I inserted after the 
> call to to _become_active() in the constructor. A printf inserted into 
> the singleton method after the Core_thread creation never shows up on 
> the console. The initialization never completes.
> 
> The AM437x is a Cortex-A9MP platform with a single core. It is very 
> similar to the Panda board as far as memory mapping goes.
> 
> Any hints on how to debug this situation further would be very helpful.

Hmm, that sounds really strange. The only thing that is done between
leaving the "Core_thread" constructor, and landing within the
"Core_thread::singleton" function again, is the call of
"__cxa_guard_release", which marks the static object as being
constructed successfully. Of course, you can add printings there too.
You can apply patch [1] to your branch, then compile core, and search
for the guard variable of the Core_thread object like this:

  genode-arm-nm bin/core | sort | c++filt | grep Core_thread::singleton

Take the address of the guard variable displayed, and replace the
address "0xdeadbeef" within the patch with the address of the guard
variable you've found. Thereby you can verify whether
__cxa_guard_release is still executed successfully.

Maybe the kernel provokes a page-fault (due to some caching issues or
whatever)? To detect a kernel page-fault you can use the kernel lock,
that has no real use on a single-core system. It is used to synchronize
different cores only. Therefore, if you detect that the kernel lock is
still locked you know that the kernel was entered although you were in
kernel mode just before. The patch [2] uses this knowledge. It extends
the kernel lock by printing some exception information, when the kernel
enters its lock twice.

Regards
Stefan

[1] http://pastebin.com/C7gSVG6e
[2] http://pastebin.com/qLkuZr0f

> 
> Thanks,
>          Bob Stewart
> 
> 
> 
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-- 
Stefan Kalkowski
Genode Labs

http://www.genode-labs.com/ · http://genode.org/