at a user mode linux image I observed it.
Created attachment 293623 [details]
old releases of libffi are never intresting unless you have a patch. try 3.0.11_rc2 (or preferably upstream git)
the discussion about libffi-3.0.11_rc2 and git test failures is going on at
"libffi-discuss" mailing list:
so they can be fixed in time for 3.0.11 release.
dev-libs/libffi-3.0.11_rc2 passes tests fine