x86emul: catch exceptions occurring in stubs

x86emul: catch exceptions occurring in stubs

Before adding more use of stubs cloned from decoded guest insns, guard
ourselves against mistakes there: Should an exception (with the
noteworthy exception of #PF) occur inside the stub, forward it to the
guest.

Since the exception fixup table entry can't encode the address of the
faulting insn itself, attach it to the return address instead. This at
once provides a convenient place to hand the exception information
back: The return address is being overwritten by it before branching to
the recovery code.

Take the opportunity and (finally!) add symbol resolution to the
respective log messages (the new one is intentionally not being coded
that way, as it covers stub addresses only, which don't have symbols
associated).

Also take the opportunity and make search_one_extable() static again.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>