Handling guard tag loss

A method comprising:

• performing a tag-guarded memory access in response to a received target address, the tag-guarded memory access comprising the steps of:
• retrieving a guard tag stored in association with a block of one or more memory locations comprising an addressed location identified by the received target address;
• and
• comparing an address tag associated with the received target address with the guard tag retrieved in the retrieving step,
• and, when the retrieving step is unsuccessful in retrieving the guard tag, causing storage of a substitute guard tag value as the guard tag stored in association with the block of one or more memory locations comprising the addressed location identified by the target address.

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

• memory access logic to perform a tag-guarded memory access in response to a received target address, the tag-guarded memory access comprising:
• a guard-tag retrieval operation to retrieve a guard tag stored in association with a block of one or more memory locations comprising an addressed location identified by the received target address;
• and
• a guard-tag check operation of comparing an address tag associated with the received target address with the guard tag retrieved by the guard-tag retrieval operation,
• wherein the memory access logic is responsive to the guard-tag retrieval operation being unsuccessful in retrieving the guard tag to cause storage of a substitute guard tag value as the guard tag stored in association with the block of one or more memory locations comprising the addressed location identified by the target address.