Apparatus and method for capability-based processing

A method comprising:

• executing program instructions stored at respective memory addresses, processing of the program instructions being constrained by a prevailing capability defining at least access permissions to a set of one or more memory addresses;
• performing a control flow change operation, the control flow change operation defining a control flow change target address indicating the address of a program instruction for execution after the control flow change operation;
• determining, in dependence on the control flow change target address, an address at which capability access permissions data is stored;
• retrieving the capability access permissions data;
• and
• generating a capability for use as a next prevailing capability in dependence upon at least the capability access permissions data, and in which:
• each capability comprises at least a pointer and data defining access permissions to the set of memory addresses;
• and
• the pointer is generated in dependence upon the control flow change target address and to generate the data defining access permissions to the set of memory addresses in dependence upon the capability access permissions data.

A computer program for controlling a host data processing apparatus to provide an instruction execution environment comprising:

• processor logic to execute program instructions stored at respective memory addresses, processing of the program instructions being constrained by a prevailing capability defining at least access permissions to a set of one or more memory addresses;
• the processor logic comprising:
• control flow change handling logic to perform a control flow change operation, the control flow change operation defining a control flow change target address indicating the address of a program instruction for execution after the control flow change operation;
• and
• capability generating logic to determine, in dependence on the control flow change target address, an address at which capability access permissions data is stored;
• the capability generating logic being configured to retrieve the capability access permissions data and to generate a capability for use as a next prevailing capability in dependence upon at least the capability access permissions data, and in which:
• each capability comprises at least a pointer and data defining access permissions to the set of memory addresses;
• and
• the pointer is generated in dependence upon the control flow change target address and to generate the data defining access permissions to the set of memory addresses in dependence upon the capability access permissions data.