Capability-generating address calculating instruction

A data processing method for an apparatus comprising processing circuitry hardware and a plurality of capability registers including a result capability register, each capability register to store a capability comprising a pointer and constraint metadata for constraining valid use of the pointer or the capability, the capability registers including a program counter capability register for which the pointer represents a program counter address indicative of a current point of program flow;

• the data processing method comprising:
• in response to a capability-generating address calculating instruction specifying an offset value, controlling the processing circuitry hardware to:
• select a reference capability register as one of the program counter capability register and a further capability register;
• and
• write to the result capability register a result capability for which the pointer of the result capability indicates a window address identifying a selected window within an address space, where a window comprises a contiguous block of addresses of a predetermined size, the selected window is offset from a reference window by a number of windows determined based on the offset value specified by the capability-generating address calculating instruction, and the reference window comprises the window which comprises an address indicated by the pointer of the reference capability register.

A non-transitory computer-readable storage medium comprising a computer program to control a host data processing apparatus to provide an instruction execution environment for execution of target code, the computer program comprising:

• instruction decoding program logic to decode instructions of the target code to control the host data processing apparatus to perform data processing;
• and
• register maintenance program logic to maintain a data structure representing a plurality of capability registers including a result capability register, each capability register to store a capability comprising a pointer and constraint metadata for constraining valid use of the pointer or the capability, the capability registers including a program counter capability register for which the pointer represents a program counter address indicative of a current point of program flow;
• in which:
• in response to a capability-generating address calculating instruction specifying an offset value, the instruction decoding program logic is configured to control the host data processing apparatus to:
• select a reference capability register as one of the program counter capability register and a further capability register;
• and
• write to the result capability register a result capability for which the pointer of the result capability indicates a window address identifying a selected window within an address space, where a window comprises a contiguous block of addresses of a predetermined size, the selected window is offset from a reference window by a number of windows determined based on the offset value specified by the capability-generating address calculating instruction, and the reference window comprises the window which comprises an address indicated by the pointer of the reference capability register.