Debug Privilege-Level Switching Instruction for Processor Circuitry
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Solution Overview
Problem
Debugging complex data processing apparatuses with multiple processors and operating modes becomes increasingly challenging due to the complexity of transitioning between different privilege levels, which is essential for identifying and eliminating defects.
Innovation Solution
A dedicated debug privilege-level switching instruction is introduced, allowing the processor to switch between privilege levels only in debug mode, preventing execution in non-debug mode, thereby simplifying the debugging process by avoiding branch operations and maintaining correct separation between privilege levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a dedicated debug privilege-level switching instruction is introduced, then the ability to switch between privilege levels in debug mode is improved, but the instruction set complexity increases
Solution Approach 1:
The solution segments the privilege level switching functionality by creating a dedicated instruction specifically for debug mode operations. This separates debug mode privilege switching from non-debug mode operations, allowing the instruction to be highly optimized for debugging purposes while maintaining clear functional boundaries. The dedicated instruction handles only the specific case of privilege level transitions during debugging, rather than attempting to handle all privilege switching scenarios.
Solution Approach 2:
The debug privilege-level switching instruction acts as an intermediary mechanism between the debugger and the processing circuitry. It provides a controlled interface that allows the debugger to switch privilege levels without exposing the complexities of privilege management to user-mode software. The instruction mediates between the debugger's debugging needs and the processor's security architecture, enabling efficient debugging while maintaining system integrity.
2Adaptability or versatility
If privilege level switching is enabled in non-debug mode, then operational flexibility is improved, but security and correctness of privilege separation deteriorates
Solution Approach 1:
The solution inverts the typical approach by making the debug privilege-level switching instruction unavailable in non-debug mode. Instead of allowing universal privilege switching with mode-dependent behavior, the instruction is designed to execute only in debug mode. This inversion ensures that privilege level separation is maintained in normal operation while providing full flexibility during debugging, as the instruction cannot accidentally execute or cause security issues in user mode.
Solution Approach 2:
The solution applies local quality by giving the debug privilege-level switching instruction different availability characteristics in different operational modes. The instruction has high functionality and flexibility when executed in debug mode, but is completely blocked in non-debug mode. This localized availability ensures that the security-critical property of privilege separation is maintained in normal operation while allowing full operational flexibility when debugging is actively performed.
3Reliability
If branch operations are used for privilege level switching, then correct privilege separation is improved, but debugging efficiency deteriorates
Solution Approach 1:
The solution extracts the branch operation requirement from the privilege level switching process specifically for debug mode. By creating a dedicated debug privilege-level switching instruction, the patent removes the need for branch operations that would normally be required to maintain privilege separation. This extraction allows privilege level transitions during debugging to occur without the overhead and complexity of branch instructions, significantly improving debugging efficiency while maintaining correctness through the dedicated instruction's design.
Data Source
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AI summary
A data processing apparatus is provided comprising processing circuitry and instruction decoding circuitry. The data processing apparatus is capable of operating at a plurality of different privilege. Processing circuitry of the data processing apparatus imposes on program instructions different access permissions to at least one of a memory and a set of registers at different ones of the different privilege levels. A debug privilege- level switching instruction is provided and decoding circuitry is responsive to this instruction to switch the processing circuitry from a current privilege level to a target privilege level if the processing circuitry is in a debug mode. However, if the processing circuitry is in a non-debug mode the instruction decoding circuitry prevents execution of the privilege-level switching instruction regardless of the current privilege level.