kernel/userspace: Move syscall_frame field to thread struct

The syscall exception frame was stored on the CPU struct during
syscall execution, but that's not right.  System calls might "feel
like" exceptions, but they're actually perfectly normal kernel mode
code and can be preempted and migrated between CPUs at any time.

Put the field on the thread struct.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
5 files changed