Exception handling in a data processing apparatus having a secure domain and a less secure domain

A data processing apparatus comprising:

• means for performing data processing operations in at least a first domain and a second domain, the processing means comprising means for controlling exception processing, wherein when operating in the first domain the means for performing data processing operations has access to data which is inaccessible to the means for performing data processing operations when operating in the second domain;
• and
• a plurality of means for storing data, the means for storing data including a first subset of means for storing data and a second subset of means for storing data;
• wherein in response to an initial exception from background processing performed by the means for performing data processing operations, the means for controlling exception processing is configured to perform state saving of data from the first subset of means for storing data before the means for performing data processing operations performs an exception handling routine corresponding to the exception, wherein the exception handling routine has responsibility for performing state saving of data from the second subset of means for storing data;
• and
• in response to a first exception causing a transition from the first domain to the second domain, where the background processing was performed by the means for performing data processing operations in the first domain, the means for controlling exception processing is configured to perform additional state saving of the data from the second subset of means for storing data before triggering the means for performing data processing operations to perform the exception handling routine in the second domain.

A data processing method for a data processing apparatus comprising processing circuitry configured to perform data processing operations in at least a first domain and a second domain, the processing circuitry comprising exception control circuitry for controlling exception processing, and a plurality of registers for storing data, the registers including a first subset of registers and a second subset of registers, wherein when operating in the first domain the processing circuitry has access to data which is inaccessible to the processing circuitry when operating in the second domain;

• the method comprising the steps of:
• in response to an initial exception from background processing performed by the processing circuitry, the exception control circuitry performing state saving of data from the first subset of registers before the processing circuitry performs an exception handling routine corresponding to the exception, wherein the exception handling routine has responsibility for performing state saving of data from the second subset of registers;
• and
• in response to a first exception causing a transition from the first domain to the second domain, where the background processing was performed by the processing circuitry in the first domain, the exception control circuitry performing additional state saving of the data from the second subset of registers before the processing circuitry performs the exception handling routine in the second domain.