Call stack sampling

A method of data processing comprising:

• performing data processing operations, wherein the data processing operations comprise subroutines;
• storing a call stack comprising subroutine information relating to subroutines which have been called during the data processing operations and have not yet returned;
• storing a stack pointer, wherein a current value of the stack pointer is indicative of an extremity of the call stack associated with a most recently called subroutine which has been called during the data processing operations and has not yet returned;
• performing a call stack sampling procedure comprising accessing the call stack with reference to the stack pointer in response to a call stack sampling trigger;
• storing a tide mark pointer, wherein a value of the tide mark pointer is indicative of a previous value which the stack point had when the call stack sampling procedure was last completed;
• modifying the tide mark pointer to match a modified value of the stack pointer in response to performance of the call stack sampling procedure;
• and
• modifying the tide mark pointer to match the current value of the stack pointer resulting from the removal of subroutine information from the call stack,
• wherein performing the call stack sampling procedure comprises retrieving subroutine information indicated between the value of the tide mark pointer and the current value of the stack pointer.

Apparatus comprising:

• means for performing data processing operations, wherein the data processing operations comprise subroutines;
• means for storing a call stack comprising subroutine information relating to subroutines which have been called during the data processing operations and have not yet returned;
• means for storing a stack pointer, wherein a current value of the stack pointer is indicative of an extremity of the call stack associated with a most recently called subroutine which has been called during the data processing operations and has not yet returned;
• means for performing a call stack sampling procedure comprising accessing the call stack with reference to the stack pointer in response to a call stack sampling trigger;
• means for storing a tide mark pointer, wherein a value of the tide mark pointer is indicative of a previous value which the stack point had when the call stack sampling procedure was last completed;
• means for modifying the tide mark pointer to match a modified value of the stack pointer in response to performance of the call stack sampling procedure;
• and
• means for modifying the tide mark pointer to match the current value of the stack pointer resulting from the removal of subroutine information from the call stack,
• wherein performing the call stack sampling procedure comprises retrieving subroutine information indicated between the value of the tide mark pointer and the current value of the stack pointer.