Operating a trace procedure for a computer program

A method comprising:

• operating a trace procedure, the trace procedure tracing execution of a computer program in a trace buffer using a program stack, the computer program using different callable modules, and the trace buffer being distinct from the program stack, wherein the trace buffer is a last-in, first-out data structure, the program stack is used to store trace buffer information and an execution error state, and the callable modules comprise calls of the trace procedure, the operating comprising:
• (i) when entering execution of a callable module on the program stack, tracing the callable module using the trace buffer, and storing in a current stack frame of the program stack a current write position of the trace buffer, the current write position indicating the write position of the trace buffer at time of entering execution of the callable module, and storing an associated execution error flag in the current frame of the stack, the associated execution error flag being stored as a cleared error flag representative of no execution error;
• (ii) in case of an execution error condition occurring during execution of the callable module, setting the associated execution error flag in the current frame of the stack to indicate the execution error condition;
• and
• (iii) when leaving execution of the callable module:
• determining if the associated execution error flag in the current frame of the stack is set based on an execution error occurring, and based on the associated execution error flag not being set, then changing the trace buffer by rewinding the trace buffer to the write position stored in the current frame of the stack, thereby removing trace of the callable module from the trace buffer;
• based on the execution error flag in the current frame not being set, further rolling back reference in the stack to the trace buffer by deleting from the stack the current write position of the trace buffer and the associated execution error flag in the current frame of the stack;
• and
• wherein when leaving execution of the callable module and the associated execution error flag is set in the current frame of the stack, leaving the write position of the trace buffer unchanged, thereby leaving trace of the callable module in the trace buffer.