Currently call gates are always treated as 32-bit gates.  In IA-32e mode
(either compatibility or 64-bit submode), system segment descriptors are
always 64-bit.  Treating them as 32-bit has the expected unfortunate
effect: only the lower 32 bits of the offset are loaded, the stack
pointer is truncated, a bad new stack pointer is loaded from the TSS (if
switching privilege levels), etc.

This change adds support for 64-bit call gate to the lcall and ljmp
instructions.  Additionally, there should be a check for non-canonical
stack pointers, but I've omitted that since there doesn't seem to be
checks for non-canonical addresses in this code elsewhere.

I've left the raise_exception_err_ra lines unwapped at 80 columns to
match the style in the rest of the file.
Signed-off-by: NAndrew Oates <aoates@google.com>
Message-Id: <20180819181725.34098-1-andrew@andrewoates.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>