Reporting delayed coprocessor exceptions to code threads having caused the exceptions by saving and restoring exception state during code thread switching

摘要

Save-Exception-State and Restore-Exception-State primitives are defined in the operating system and are used to confine the reporting of delayed asynchronous coprocessor exceptions to the respective code threads that generate the exceptions. The Save-Exception-State primitive saves the coprocessor exception state pertinent to the currently executed code thread, and the Restore-Exception-State primitive restores a selected one of the exception states having been saved. The Save- Exception-State primitive synchronizes the coprocessor, disables use of the coprocessor, saves any pending coprocessor exception state into memory, and clears the coprocessor exception state information from the coprocessor or a "thread descriptor" area of memory allocated to the current code thread. The Restore-Exception-State primitive synchronizes the coprocessor, disables use of the coprocessor, reports any pending exceptions in the coprocessor, and restores the saved exception state into a respective code thread descriptor in memory allocated to the code thread having generated the saved exception state information. The restored exception state is reported by a "Coprocessor-Disabled" exception handler that checks for any exceptions pending in the coprocessor or thread descriptor, when necessary stores the coprocessor state information from the process which last executed a coprocessor instruction, when necessary retrieves the coprocessor state information for the current process, reports any pending exceptions, and reenables use of the coprocessor.