OS Debugging Method Using a Lightweight Virtual Machine Monitor

OS Debugging Method Using a Lightweight Virtual Machine Monitor Tadashi Takeuchi Hitachi Systems Development Laboratory, Japan t-takeu@sdl.hitachi.co.jp Abstract Demands for implementing original OSs that can achieve high I/O performance on PC/AT compatible hardware have recently been increasing, but conventional OS debugging environments have not been able to simultaneously assure their stability, be easily customized to new OSs and new I/O devices, and assure efficient execution of I/O operations. We therefore developed a novel OS debugging method using a lightweight virtual machine. We evaluated this debugging method experimentally and confirmed that it can transfer data about 5.4 times as fast as the conventional virtual machine monitor. 1. Introduction Many appliance servers using original real-time operating systems (OSs) and achieving high-performance I/O on PC/AT compatible hardware have been marketed recently. One result of this trend is increasing demand for efficient debugging environments for original OSs to support various I/O devices and efficient debugging mechanisms monitoring the OS status tracing even while the OS is executing high-throughput I/O operations. Because the vendors of PC/AT-compatible hardware do not provide debugging hardware such as ICE, the only debugging environments available for operating systems running on PCs are a hardware simulator working with a software debugger, a software remote debugger, and a software debugger embedded in the operating system under development. These environments, however, cannot simultaneously assure their stability when the operating system under development does not perform properly, be easily customized for different operating systems and new I/O devices, and assure efficient execution of I/O operations. We therefore developed a novel OS debugging environment and method that can satisfy the above three demands simultaneously by using a lightweight virtual machine monitor. In this paper, we describe our new environment and method and report the results of experiments comparing its performance with that of conventional debugging environments. 2. Debugging Method Our new debugging method provides the debugging environment shown in Fig. 2.1. Software remote debugger General-purpose OS Communi- cation Device Communi- cation device Remote debugging functions (Stub) Interruption controller Timer Debugging commands Interruption- controller emulator Timer emulator CPU- resources emulator Page/ interruption handling table, etc. Real Hardware Interfaces Original OS Indirect access Other I/O devices Direct access Lightweight Virtual Machine Monitor Host Machine Target Machine Software remote debugger General-purpose OS Communi- cation Device Communi- cation device Remote debugging functions (Stub) Interruption controller Timer Debugging commands Interruption- controller emulator Timer emulator CPU- resources emulator Page/ interruption handling table, etc. Real Hardware Interfaces Original OS Indirect access Other I/O devices Direct access Lightweight Virtual Machine Monitor Host Machine Target Machine Figure 2.1 Architecture of debugging environment The architecture of our debugging environment is similar to the one used for conventional remote debugging. It consists of a host machine and a target machine. A software remote debugger running on the host machine receives debugging commands (target machine memory/register reference/updating, etc.) from a user and sends the command to the target machine The target machine architecture differs from that of classical software remote debugging in that a lightweight virtual machine monitor implemented independently of original OSs is embedded in it. The monitor provides remote debugging functions such as reception and execution of the debugging commands. The monitor also provides a partial hardware emulation mechanism. It emulates only the hardware resources used by the remote debugging function (such as the interruption controller or interruption-handling table). The monitor provides the same interfaces as the real Proceedings of the Design, Automation and Test in Europe Conference and Exhibition (DATE’05) 1530-1591/05 $ 20.00 IEEE hardware, so it can work with any OSs running on PC/AT architectures. The hardware resources used by the remote debugging functions are accessed by the original OS via the lightweight virtual machine monitor, so stability of the debugging environment can be assured because the real hardware remain in normal states even if the original OS works improperly because it has bugs. The other devices, however, especially high-throughput I/O devices (such as a SCSI controller or Ethernet controller) can be accessed directly by the original OS. This direct access enables I/O operations to be executed efficiently in this debugging environment. The direct access also makes it unnecessary for the monitor to emulate the high-throughput I/O devices, so this deb

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