Liang A-lei

FATTY: A Reliable FAT File System

Most portable digital devices use the conventional FAT file system because of its compatibility. However, the FAT file system is unreliable across system crashes and power failures. This paper proposes the delayed sequential write method to improve the FAT file system s reliability. Compared to other methods such as synchronous write and logging, the DSW method is simple and effective. Simulation results show that it is also quite efficient, about 50-80% better than synchronous write.

Return Instruction Analysis and Optimization in Dynamic Binary Translation

Dynamic Binary Translation (DBT) is widely re-searched and used to support legacy binary code, pro-vide program instrumentation, improve code performance, and so on. The performance of a DBT system is always an essential issue. And a major source of over-head is the execution of the indirect branch in source code, because it requires extra instructions to resolve the target address. In this paper, we present an improved return cache scheme with relative low overhead to handle the return instruction, the most important form of indirect branch. On dealing with the source return instruction, the overhead caused by our method is only 1%~4% to the native execution for most SPEC CPU2000 INT benchmarks (2.5% on average), which is acceptable in a DBT system.

A Two-Phase Optimization Approach for Condition Codes in a Machine Adaptable Dynamic Binary Translator

Condition codes (CCs) are special architected bits that characterize instruction results. Reducing the overhead of emulating condition codes is a critical performance issue in binary translation. In this paper, we propose a two-phase optimization approach for condition codes, which has been implemented in Crossbit—a machine adaptable dynamic binary translator (DBT). First, redundant flag computing code in a basic block is reduced based on the information collected by Crossbit when the block is identified. Then, lazy evaluation technique is used inter basic blocks, which make the condition codes emulation more efficient. Experimental results show that this method works much better than the straightforward emulation method—it eliminate the code size more than 20% and have a performance gain nearly 40% in Crossbit. The data proves that the approach is effective to remove the redundant code and to increase the performance of the translated code.

The Implementation of Dynamic Linking in Dynamic Binary Translation Systems

Dynamic binary translation (DBT) is a commonly used technology in virtual machines. Most DBT systems, like Dynamo, can only translate programs statically linked but not ones dynamically linked. Statically linked programs will lead to expansion of binary codes, which is the indirect reason of loss on performance. In this paper, we propose an approach to implement dynamic linking on DBT systems. During the research, we came across some challenges related with operating systems, compilation and architecture, which will be discussed later in detail. And we have developed a module and had it tested on our DBT system, CrossBit. The statistics show that CrossBit with dynamic linking reduces the number of translated blocks and execution time.