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 that statement…

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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. The extracted information can later be used for white-box testing. 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.…

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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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File system, RTEMS, RTOS, Software

Setting up YAFFS2 and JFFS2 on RTEMS with flash simulated on a RAM-disk

Hi all, In this post, we’ll look forward to setting up flash file systems namely JFFS2 and YAFFS2 on RTEMS with flash simulated on a RAM-disk. For file system benchmarking purposes, we didn’t actually use them on a real flash(as to eliminate the effect of flash driver’s performance) but implementing them on a real flash won’t be very different from the process given in the later sections of this post. So, let’s begin with JFFS2 first: JFFS2 on RTEMS First reference you will see is of testsuites/fstests/jffs2_support/fs_support.c . Configuration here works up to a large extent unless the size of…

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GSoC, RTEMS, Software

GSoC 2018: Final Report

This is the final report of the work done under GSoC’18 with the RTEMS community. I’ll begin with a summary of all the work done during this summer and will then move towards the corresponding code and documentation developed throughout the timeline.   Porting SDIO driver to RTEMS and benchmarking Student:- Udit Kumar Agarwal Mentors:- Christian Mauderer, Punit Vara Original proposal link: Here Weekly updates:- https://devel.rtems.org/wiki/GSoC/2018#UditkumarAgarwal Project tickets:-  ticket#3429, ticket#3430, ticket#3428 Github Repository:– https://github.com/madaari/GSoC-rtems-18 ABSTRACT RTEMS, being an open-source hard real-time operating system, is already supported by a vast community of developers, hobbyists, and industrialists. With its full application, it…

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ARM, Benchmark, File system, FIO, GSoC, RTEMS, Software

Benchmarking RTEMS Filesystems using FIO

Hi, In this post we will explore FIO’s RTEMS port and how it can be used to benchmark RTEMS filesystems and drivers. First, let’s have a quick look at all the RTEMS filesystems: RTEMS FILESYSTEMS RTEMS supports mainly two types of filesystems: Network and Physical fs. Benchmarking support for networking filesystems isn’t yet available. However, nearly every other physical filesystem can be benchmarked and contrasted. Heap-based file systems are those which uses malloc() for file allocation. In other words, they reside completely on heap memory. These are mainly used to provide basic directory/file management even if there is no dedicated…

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Benchmark, FIO, GSoC, RTEMS, Software

[GSoC Phase-1] Porting FIO to RTEMS

Hi all, This post covers most of my learnings during phase one of GSoC with RTEMS. My main goal of phase 1 was to port an IO benchmark to RTEMS. Towards this, various benchmarks were compared and fio was finalized for the import. FIO is a pretty much widely accepted and highly configurable IO benchmarking tool, which supports a number of large number of different OS and now RTEMS is among one of them. Following were the major considerations i learned while porting a 3rd party user-space tool to RTEMS(I’ll try to generalize as much as possible, but there will…

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