In Yocto Project 5.8 kernel pycrash produces the following exception:

Loading tasks...crash-python: Failed to open /home/skamensk/oe/20201017/build/vmcore.  No method to retrieve last run from task found.
Traceback (most recent call last):
  File "<string>", line 38, in <module>
  File "./build/lib/crash/session.py", line 33, in __init__
    self.kernel.setup_tasks()
  File "./build/lib/crash/kernel.py", line 691, in setup_tasks
    ltask = LinuxTask(task)
  File "./build/lib/crash/types/task.py", line 229, in __init__
    self._init_task_types(task_struct)
  File "./build/lib/crash/types/task.py", line 269, in _init_task_types
    cls._pick_last_run()
  File "./build/lib/crash/types/task.py", line 604, in _pick_last_run
    raise RuntimeError("No method to retrieve last run from task found.")
RuntimeError: No method to retrieve last run from task found.

It turns out that Yocto Project 5.8 kernel does not enable CONFIG_TASKSTATS
and CONFIG_TASK_DELAY_ACCT as result CONFIG_SCHED_INFO is not selected,
as a result this raises the aformentioned exception because struct sched_info
does not have any fields in this case. To work around this
the raising of the RuntimeError was replaced with a print out that states
which CONFIGS must be enabled and cls._get_last was set to a function that
will always return 0.

'pyps -l' functionality is important but there are plenty of other useful
funcationality even if we cannot figure out last run time of task.

Signed-off-by: Alexander Kamensky <alexander.kamensky42@gmail.com>

In Yocto 5.8 kernel it was observed that pycrash produces the following
exception:

...
  File "/home/skamensk/crash-python/20201101/crash-python/build/lib/crash/commands/kmem.py", line 28, in <module>
    from crash.types.slab import kmem_cache_get_all, kmem_cache_from_name
...
  File "/home/skamensk/crash-python/20201101/crash-python/build/lib/crash/types/slab.py", line 328, in check_kmem_cache_type
    cls.percpu_name = find_member_variant(gdbtype, ['cpu_cache', 'array'])
  File "/home/skamensk/crash-python/20201101/crash-python/build/lib/crash/util/__init__.py", line 304, in find_member_variant
    raise TypeError("Unrecognized '{}': could not find member '{}'"
TypeError: Unrecognized 'struct kmem_cache': could not find member 'cpu_cache'

Yocto Project 5.8 Kernel configured with CONFIG_SLUB. In this case struct
kem_cache does not have field cpu_cache, so lookup of this field fails in
such configuration.

Workaround is to check kernel config if CONFIG_SLUB is enabled and skip slab
specif functionality if that is the case.

TODO: Implement slub analogs for slab operations.

Signed-off-by: Alexander Kamensky <alexander.kamensky42@gmail.com>