Freelist corruption results in the "slabinfo" module crashing. Since
this is a common symptom of use-after-free bugs, we'd rather give useful
information about this case. So don't crash the module. Catch the error
and report corruption issues at the end.

This also helps in certain cases where we are running against a live
kernel, and the freelist is not corrupt, but it changed by the time we
decoded the pointer. As a result, we print different messages at
different times: for live systems, we say this may be transient, but for
core dumps, we say it indicates a potential use-after-free bug.

To do this, we have to implement a rather sketchy workaround to use the
_SlabCacheHelperSlub from drgn. This is manually verified to work on
0.0.25 through 0.0.27, which are the only supported drgn versions. But,
we need to work on upstream tweaks to improve the slab helpers, so we
don't need to rely on the hack.

Signed-off-by: Stephen Brennan <[email protected]>

Signed-off-by: Stephen Brennan <[email protected]>