Tag protecting instruction

A method comprising:

• performing data processing operations in response to instructions,
• in response to a memory access instruction identifying an address pointer, issuing a memory access request comprising a request to access data stored at a memory location identified by a memory address determined based on an address portion of the address pointer;
• in response to the memory access request, comparing a tag value determined based on a tag portion of the address pointer with an allocation tag associated with the memory location identified by the memory address and, in response to the comparison indicating a given result, performing a tag error response;
• in response to a tag protecting instruction identifying an input operand, performing an operation in respect of the input operand to generate an output value;
• detecting whether the operation involved an attempt to set the value of at least one bit in an identified portion of the output value to a value other than a value in a corresponding bit position in the input operand;
• and
• in response to detecting that the operation involved the attempt to set the value of at least one bit in the identified portion of the output value to the value other than the value in a corresponding bit position in the input operand, setting at least a given portion of the output value to an error-indicating value,
• wherein the identified portion is a portion of the output value which would be used as the tag portion if the output operand was used as the address pointer for the memory access instruction.

A computer program comprising instructions which, when executed by a host data processing apparatus, control the host data processing apparatus to provide an instruction execution environment for executing target program code, the computer program comprising:

• processing program logic to perform data processing operations in response to instructions in the target program code,
• wherein the processing program logic is responsive to a memory access instruction identifying an address pointer to issue a memory access request comprising a request to access data stored at a memory location identified by a memory address determined based on an address portion of the address pointer;
• and
• access control program logic responsive to the memory access request to compare a tag value determined based on a tag portion of the address pointer with an allocation tag associated with the memory location identified by the memory address and, in response to the comparison indicating a given result, to perform a tag error response,
• wherein:
• the processing program logic is responsive to a tag protecting instruction identifying an input operand to perform an operation in respect of the input operand to generate an output value;
• the processing program logic is configured to detect whether the operation involved an attempt to set the value of at least one bit in an identified portion of the output value to a value other than a value in a corresponding bit position in the input operand;
• the processing program logic is configured to set, in response to detecting that the operation involved the attempt to set the value of at least one bit in the identified portion of the output value to the value other than the value in a corresponding bit position in the input operand, at least a given portion of the output value to an error-indicating value;
• and
• the identified portion is a portion of the output value which would be used as the tag portion if the output operand was used as the address pointer for the memory access instruction.