Cross-domain call system in a capability based digital data processing system

In a digital data processing system including a calling program and an associated domain, a called program and an associated domain, and a plurality of registers, a cross-domain transfer system comprising:

• A. cross-domain stack means having a plurality of stack frames including a stack frame that corresponds to said domain of said calling program;
• B. means for identifying a subset of said registers having contents that are to be unavailable to said called program, access to said means for identifying being restricted to that said calling program and said called program cannot change said subset;
• C. cross-domain call means associated with said calling program including means for saving the contents of said subset of said registers in said stack frame that corresponds to said domain of said calling program and clearing said subset of said registers during a cross-domain call operation to said called program;
• D. cross-domain return means for retrieving the contents of said subset of registers which were previously saved by said cross-domain call means in said stack frame during a cross-domain return operation from said called program to said calling program and restoring said contents in said registers.

In a digital processing system including a calling program and an associate domain and a called program and an associated domain, and a plurality of registers available for use by said calling program and said called program, linkage means comprising:

• A. calling program inspection means for identifying said registers that are used by said calling program;
• B. called program inspection means for identifying said registers that are used by said called program;
• C. linkage information generation means responsive to identification of said registers by said calling program inspection means and said called program inspection means for generating linkage information that identifies registers having contents that will be changed when said calling program calls said called program, access to said linkage information being restricted so that said calling and said called programs cannot change said linkage information;
• and
• D. means for providing said linkage information to said calling program and said called program during cross-domain transfers and causing the contents of only said identified registers to be saved during said call, whereby other registers having contents that will not be changed during said call are not saved.

In a digital data processing system including a calling program and an associated domain and a called program and an associated domain, and a plurality of registers available for use by said calling program and said called program, linkage means comprising:

• A. calling program inspection means for identifying said registers that are used by said calling program;
• B. called program inspection means for identifying said registers that are used by said called program;
• C. linkage information generation means responsive to identification of said registers by said called program inspection means and said called program inspection means for generating linkage information that identifies registers having contents that will be changed when said calling program calls said called program, access to said linkage information being restricted so that said calling and said called programs cannot change said linkage information;
• and
• D. means for providing said linkage information to said calling program and said called program during cross-domain transfers and causing the contents of only said identified registers to be saved during said call, whereby other registers having contents that will not be changed during said call are not saved;
• wherein said calling program and said called program further have an associated trust rating, said linkage means generating said linkage information based at least in part on said trust rating so that said identified registers also include registers having contents that are to be unavailable to said called program during a cross-domain transfer from said calling program, said means for providing clearing the contents of said registers to be made unavailable during said call.