Bugs, Compiler, Concurrency, Software, static analysis, verification

A survey of concurrency bug patterns

Humans tend to make the same mistake again and again. We, software developers, are no different. Hello everyone, in this blog post, I’m going to talk about common concurrency bug patterns. Bug patterns give good insight into developer’s psychology, specifically, the assumptions we make about the programming languages, compilers, 3rd party code, OS scheduler, and hardware architecture.

Multi-Processor Programming, Software

From Linearizability to CAP Theorem: A Brief Overview of Consistency Guarantees in Concurrent Programs

Concurrent systems, including both multiprocessor and distributed systems, often rely on object replication for improving performance and scalability. Object replication, the idea of keeping multiple local copies of shared data structures, demands another sub-system that ensures consistency between these local copies in real-time!! Network delays in distributed systems and overlapping operations on shared data structures within multiprocessor systems are some of the major challenges in ensuring consistency. To overcome these issues, without sacrificing correctness and performance, the research community has proposed various “relaxations” in the consistency requirement that I intend to cover in the next few sections. Following is the…

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Compiler, LLVM, Pass, Software

Writing Your First LLVM Pass and Registering it in the Clang Toolchain

There are several detailed tutorials[1] on writing an LLVM pass so that I won’t cover it in much detail. However, as of today(May 2020), there is no detailed guide on registering an LLVM pass within the OPT and Clang toolchains. So, this post will be mainly regarding that. Content: Introduction Types of LLVM passes Writing a basic function pass in LLVM Registering a pass within the OPT toolchain Clang toolchain Introduction LLVM is an extremely modular compiler infrastructure that provides back-end tools for code optimization and transformation. It works on an intermediate representation called LLVM IR. Clang, on the other…

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DDoS, Software

DDoS Defense Triad

Distributed Denial Of Service(DDoS) is one of the most disruptive cybercrimes that can cause substantial financial loss to its the victim. Recent DDoS attacks brought up to 1.3 Tbps of traffic with 126.9 million packets of data per second(Github, Feb 2018) and were used to serve a variety of motives ranging from financial gains to political protests, “Hacktivism.” In this post, I’ll cover three primary DDoS defense techniques that are low cost and can be easily deployed by small to medium scale businesses. Content: Intrusion prevention General Security Policy Ingress and Egress Filtering 3rd party DDoS protection services static signature…

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model checker, Software, static analysis, validation

Understanding Dependency Graphs for Program Analysis

Hi, In this blog post, I’ll briefly cover several types of dependency graphs used for program analysis, transformation, and representation. Following is the table of content: Prerequisites Reaching definition analysis Pointer analysis Dominator tree Call graphs Control flow graphs Control dependency graphs Data dependency graphs Program dependency graphs System dependency graphs Prerequisites Reaching definition analysis (RDA) RDA aims to determine the set of variable definitions (assignments) that may (or must) reach a given program point. Every program statement has an Entry set and Exit set associated with it, where the entry set is a set of all variable definitions reaching…

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model checker, Software, static analysis, validation, verification

Static Program Analysis: Motivation and Techniques

Static analysis is a method to extract specific information about the program without actually running it. In this blog post, we will first have a look at different types of information that we can obtain using static analysis. Later, we will have a comprehensive overview of different techniques for static program analysis. Motivation There are broadly two categories of information, based on their usage, that we can extract: Proscriptive information and Descriptive information[1]. Proscriptive information is obtained when we statically analyze the program behavior against a set of prescribed rules. For instance, identification, localization, and explanation of all software anomalies…

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model checker, Software, static analysis, validation, verification

Embedded Software Testing, Validation, and Verification

Embedded software, unlike general software, is highly dependent on the hardware they are developed for. Thus it became essential to create a hardware-based or hardware-like environment simultaneously with the software for effective testing. Where simulators and emulators can, up to some extent, provide a hardware-like environment for testing embedded software, they can not always be relied upon while testing for safety-critical applications like flight control system. It is this, high dependency on hardware, which makes testing, verification, and validation of embedded Softwares far more demanding than of general software. Moreover, several safety-critical embedded systems are also strictly real-time, or at…

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BTP, memristor, Software

Tutorial: CMOS-Memristor based Neural Networks

AIM: To simulate a fully functional 2 layer CMOS-Memristor-based neural network for classification of benign and malign cancer. Description: The circuit-based neural network achieved an accuracy of 94.85% compared to the 96.71% accuracy of the original network. The trained weights were programmed onto the weight blocks of the memristor bridge in this neural network. Training of neural network was done on MATLAB and then weights were extracted and accordingly memristor-bridge weight blocks were configured. In the memristor-bridge circuit, currently resistors were used but they can be replaced with memristors. For activation function, we used ReLu (Rectified Linear Unit) and in…

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OS, Software

Case Study: Symbian OS

Content Introduction Historical Development Applications Versions Type of OS Kernel in Symbian OS Architectural design of symbian OS Threads Language supported Deadlock handling File Handling Security Issues User interface User Application development environment Process synchronization Resource management INTRODUCTION Symbian is a mobile operating system developed for smartphones that were originally used for Handheld PCs. It was used by a variety of major brands like Samsung, Motorola, and most of all by Nokia. It was the most popular OS till 2010 when it was replaced by an android. Symbian consists of a variety of layers which most prominently include the User…

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