Debugging with GDB on Freebsd by John Baldwin Debuggers Are Tools Used to Inspect the State of Processes in a System
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Freebsd-And-Git.Pdf
FreeBSD and Git Ed Maste - FreeBSD Vendor Summit 2018 Purpose ● History and Context - ensure we’re starting from the same reference ● Identify next steps for more effective use / integration with Git / GitHub ● Understand what needs to be resolved for any future decision on Git as the primary repository Version control history ● CVS ○ 1993-2012 ● Subversion ○ src/ May 31 2008, r179447 ○ doc/www May 19, 2012 r38821 ○ ports July 14, 2012 r300894 ● Perforce ○ 2001-2018 ● Hg Mirror ● Git Mirror ○ 2011- Subversion Repositories svnsync repo svn Subversion & Git Repositories today svn2git git push svnsync git svn repo svn git github Repositories Today fork repo / Freebsd Downstream svn github github Repositories Today fork repo / Freebsd Downstream svn github github “Git is not a Version Control System” phk@ missive, reproduced at https://blog.feld.me/posts/2018/01/git-is-not-revision-control/ Subversion vs. Git: Myths and Facts https://svnvsgit.com/ “Git has a number of advantages in the popularity race, none of which are really to do with the technology” https://chapmanworld.com/2018/08/25/why-im-now-using-both-git-and-subversion-for-one-project/ 10 things I hate about Git https://stevebennett.me/2012/02/24/10-things-i-hate-about-git Git popularity Nobody uses Subversion anymore False. A myth. Despite all the marketing buzz related to Git, such notable open source projects as FreeBSD and LLVM continue to use Subversion as the main version control system. About 47% of other open source projects use Subversion too (while only 38% are on Git). (2016) https://svnvsgit.com/ Git popularity (2018) Git UI/UX Yes, it’s a mess. -
Introduction to Debugging the Freebsd Kernel
Introduction to Debugging the FreeBSD Kernel John H. Baldwin Yahoo!, Inc. Atlanta, GA 30327 [email protected], http://people.FreeBSD.org/˜jhb Abstract used either directly by the user or indirectly via other tools such as kgdb [3]. Just like every other piece of software, the The Kernel Debugging chapter of the FreeBSD kernel has bugs. Debugging a ker- FreeBSD Developer’s Handbook [4] covers nel is a bit different from debugging a user- several details already such as entering DDB, land program as there is nothing underneath configuring a system to save kernel crash the kernel to provide debugging facilities such dumps, and invoking kgdb on a crash dump. as ptrace() or procfs. This paper will give a This paper will not cover these topics. In- brief overview of some of the tools available stead, it will demonstrate some ways to use for investigating bugs in the FreeBSD kernel. FreeBSD’s kernel debugging tools to investi- It will cover the in-kernel debugger DDB and gate bugs. the external debugger kgdb which is used to perform post-mortem analysis on kernel crash dumps. 2 Kernel Crash Messages 1 Introduction The first debugging service the FreeBSD kernel provides is the messages the kernel prints on the console when the kernel crashes. When a userland application encounters a When the kernel encounters an invalid condi- bug the operating system provides services for tion (such as an assertion failure or a memory investigating the bug. For example, a kernel protection violation) it halts execution of the may save a copy of the a process’ memory current thread and enters a “panic” state also image on disk as a core dump. -
Process and Memory Management Commands
Process and Memory Management Commands This chapter describes the Cisco IOS XR software commands used to manage processes and memory. For more information about using the process and memory management commands to perform troubleshooting tasks, see Cisco ASR 9000 Series Aggregation Services Router Getting Started Guide. • clear context, on page 2 • dumpcore, on page 3 • exception coresize, on page 6 • exception filepath, on page 8 • exception pakmem, on page 12 • exception sparse, on page 14 • exception sprsize, on page 16 • follow, on page 18 • monitor threads, on page 25 • process, on page 29 • process core, on page 32 • process mandatory, on page 34 • show context, on page 36 • show dll, on page 39 • show exception, on page 42 • show memory, on page 44 • show memory compare, on page 47 • show memory heap, on page 50 • show processes, on page 54 Process and Memory Management Commands 1 Process and Memory Management Commands clear context clear context To clear core dump context information, use the clear context command in the appropriate mode. clear context location {node-id | all} Syntax Description location{node-id | all} (Optional) Clears core dump context information for a specified node. The node-id argument is expressed in the rack/slot/module notation. Use the all keyword to indicate all nodes. Command Default No default behavior or values Command Modes Administration EXEC EXEC mode Command History Release Modification Release 3.7.2 This command was introduced. Release 3.9.0 No modification. Usage Guidelines To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. -
Post Mortem Crash Analysis
Post Mortem Crash Analysis Johan Heander & Magnus Malmborn January 14, 2007 Abstract To improve the quality and reliability of embedded systems it is important to gather information about errors in units already sold and deployed. To achieve this, a system for transmitting error information from the customer back to the developers is needed, and the developers must also have a set of tools to analyze the error reports. The purpose of this master thesis was to develop a fully functioning demon- stration system for collection, transmission and interpretation of error reports from Axis network cameras using the Linux operating system. The system has been shown to handle both kernel and application errors and conducts automatic analysis of received data. It also uses standard HTTP protocol for all network transfers making it easy to use even on firewalled net- works. i ii Acknowledgement We would like to thank our LTH supervisor Jonas Skeppstedt for all he has taught us about computer science in general and operating systems and the C programming language in particular. We would also like to thank Mikael Starvik at Axis Communications for quickly providing us with all hardware and information we needed to complete this thesis, and for providing us with support during our implementation and writing. Finally we thank all the developers working at Axis Communications, many of whom have provided input and reflections on our work. iii iv Contents 1 Introduction 1 1.1 Problem description . 1 1.2 Problem analysis . 1 2 Background 3 2.1 Kernel crashes . 3 2.2 User space crashes . -
Getting Started With... Berkeley Software for UNIX† on the VAX‡ (The Third Berkeley Software Distribution)
Getting started with... Berkeley Software for UNIX† on the VAX‡ (The third Berkeley Software Distribution) A package of software for UNIX developed at the Computer Science Division of the University of California at Berkeley is installed on our system. This package includes a new version of the operating sys- tem kernel which supports a virtual memory, demand-paged environment. While the kernel change should be transparent to most programs, there are some things you should know if you plan to run large programs to optimize their performance in a virtual memory environment. There are also a number of other new pro- grams which are now installed on our machine; the more important of these are described below. Documentation The new software is described in two new volumes of documentation. The first is a new version of volume 1 of the UNIX programmers manual which has integrated manual pages for the distributed software and incorporates changes to the system made while introducing the virtual memory facility. The second volume of documentation is numbered volume 2c, of which this paper is a section. This volume contains papers about programs which are in the distribution package. Where are the programs? Most new programs from Berkeley reside in the directory /usr/ucb. A major exception is the C shell, csh, which lives in /bin. We will later describe how you can arrange for the programs in the distribution to be part of your normal working environment. Making use of the Virtual Memory With a virtual memory system, it is no longer necessary for running programs to be fully resident in memory. -
CS 350 Operating Systems Spring 2021
CS 350 Operating Systems Spring 2021 4. Process II Discussion 1: Question? • Why do UNIX OSes use the combination of “fork() + exec()” to create a new process (from a program)? • Can we directly call exec() to create a new process? Or, do you have better ideas/designs for creating a new process? • Hints: To answer this question: think about the possible advantages of this solution. Fork Parent process Child process Exec New program image in execution 2 Discussion 1: Background • Motived by the UNIX shell • $ echo “Hello world!” • $ Hello world! • shell figures out where in the file system the executable “echo” resides, calls fork() to create a new child process, calls exec() to run the command, and then waits for the command to complete by calling wait(). • You can see that you can use fork(), exec() and wait() to implement a shell program – our project! • But what is the benefit of separating fork() and exec() in creating a new process? 3 Discussion 1: Case study • The following program implements the command: • $ wc p3.c > p4.output # wc counts the word number in p3.c • # the result is redirected to p4.output Close default standard output (to terminal) open file p4.output 4 Discussion 1: Case study • $ wc p3.c # wc outputs the result to the default standard output, specified by STDOUT_FILENO • By default, STDOUT_FILENO points to the terminal output. • However, we close this default standard output → close(STDOUT_FILENO ); • Then, when we open the file “p4.output” • A file descriptor will be assigned to this file • UNIX systems start looking for free file descriptors from the beginning of the file descriptor table (i.e., at zero). -
The Dragonflybsd Operating System
1 The DragonFlyBSD Operating System Jeffrey M. Hsu, Member, FreeBSD and DragonFlyBSD directories with slightly over 8 million lines of code, 2 million Abstract— The DragonFlyBSD operating system is a fork of of which are in the kernel. the highly successful FreeBSD operating system. Its goals are to The project has a number of resources available to the maintain the high quality and performance of the FreeBSD 4 public, including an on-line CVS repository with mirror sites, branch, while exploiting new concepts to further improve accessible through the web as well as the cvsup service, performance and stability. In this paper, we discuss the motivation for a new BSD operating system, new concepts being mailing list forums, and a bug submission system. explored in the BSD context, the software infrastructure put in place to explore these concepts, and their application to the III. MOTIVATION network subsystem in particular. A. Technical Goals Index Terms— Message passing, Multiprocessing, Network The DragonFlyBSD operating system has several long- operating systems, Protocols, System software. range technical goals that it hopes to accomplish within the next few years. The first goal is to add lightweight threads to the BSD kernel. These threads are lightweight in the sense I. INTRODUCTION that, while user processes have an associated thread and a HE DragonFlyBSD operating system is a fork of the process context, kernel processes are pure threads with no T highly successful FreeBSD operating system. Its goals are process context. The threading model makes several to maintain the high quality and performance of the FreeBSD guarantees with respect to scheduling to ensure high 4 branch, while exploring new concepts to further improve performance and simplify reasoning about concurrency. -
Linux Core Dumps
Linux Core Dumps Kevin Grigorenko [email protected] Many Interactions with Core Dumps systemd-coredump abrtd Process Crashes Ack! 4GB File! Most Interactions with Core Dumps Poof! Process Crashes systemd-coredump Nobody abrtd Looks core kdump not Poof! Kernel configured Crashes So what? ● Crashes are problems! – May be symptoms of security vulnerabilities – May be application bugs ● Data corruption ● Memory leaks – A hard crash kills outstanding work – Without automatic process restarts, crashes lead to service unavailability ● With restarts, a hacker may continue trying. ● We shouldn't be scared of core dumps. – When a dog poops inside the house, we don't just `rm -f $poo` or let it pile up, we try to figure out why or how to avoid it again. What is a core dump? ● It's just a file that contains virtual memory contents, register values, and other meta-data. – User land core dump: Represents state of a particular process (e.g. from crash) – Kernel core dump: Represents state of the kernel (e.g. from panic) and process data ● ELF-formatted file (like a program) User Land User Land Crash core Process 1 Process N Kernel Panic vmcore What is Virtual Memory? ● Virtual Memory is an abstraction over physical memory (RAM/swap) – Simplifies programming – User land: process isolation – Kernel/processor translate virtual address references to physical memory locations 64-bit Process Virtual 8GB RAM Address Space (16EB) (Example) 0 0 16 8 EB GB How much virtual memory is used? ● Use `ps` or similar tools to query user process virtual memory usage (in KB): – $ ps -o pid,vsz,rss -p 14062 PID VSZ RSS 14062 44648 42508 Process 1 Virtual 8GB RAM Memory Usage (VSZ) (Example) 0 0 Resident Page 1 Resident Page 2 16 8 EB GB Process 2 How much virtual memory is used? ● Virtual memory is broken up into virtual memory areas (VMAs), the sum of which equal VSZ and may be printed with: – $ cat /proc/${PID}/smaps 00400000-0040b000 r-xp 00000000 fd:02 22151273 /bin/cat Size: 44 kB Rss: 20 kB Pss: 12 kB.. -
The Complete Freebsd
The Complete FreeBSD® If you find errors in this book, please report them to Greg Lehey <grog@Free- BSD.org> for inclusion in the errata list. The Complete FreeBSD® Fourth Edition Tenth anniversary version, 24 February 2006 Greg Lehey The Complete FreeBSD® by Greg Lehey <[email protected]> Copyright © 1996, 1997, 1999, 2002, 2003, 2006 by Greg Lehey. This book is licensed under the Creative Commons “Attribution-NonCommercial-ShareAlike 2.5” license. The full text is located at http://creativecommons.org/licenses/by-nc-sa/2.5/legalcode. You are free: • to copy, distribute, display, and perform the work • to make derivative works under the following conditions: • Attribution. You must attribute the work in the manner specified by the author or licensor. • Noncommercial. You may not use this work for commercial purposes. This clause is modified from the original by the provision: You may use this book for commercial purposes if you pay me the sum of USD 20 per copy printed (whether sold or not). You must also agree to allow inspection of printing records and other material necessary to confirm the royalty sums. The purpose of this clause is to make it attractive to negotiate sensible royalties before printing. • Share Alike. If you alter, transform, or build upon this work, you may distribute the resulting work only under a license identical to this one. • For any reuse or distribution, you must make clear to others the license terms of this work. • Any of these conditions can be waived if you get permission from the copyright holder. Your fair use and other rights are in no way affected by the above. -
Exniffer: Learning to Rank Crashes by Assessing the Exploitability from Memory Dump
Exniffer: Learning to Rank Crashes by Assessing the Exploitability from Memory Dump Thesis submitted in partial fulfillment of the requirements for the degree of MS in Computer Science & Engineering by Research by Shubham Tripathi 201407646 [email protected] International Institute of Information Technology Hyderabad - 500 032, INDIA March 2018 Copyright c Shubham Tripathi, March 2018 All Rights Reserved International Institute of Information Technology Hyderabad, India CERTIFICATE It is certified that the work contained in this thesis, titled “Exniffer: Learning to Rank Crashes by Assessing the Exploitability from Memory Dump” by Shubham Tripathi, has been carried out under my supervision and is not submitted elsewhere for a degree. Date Adviser: Prof. Sanjay Rawat “Contemplate and reflect upon knowledge, and you will become a benefactor to others.” To my parents Acknowledgments I would like to express my gratitude to my adviser, Dr. Sanjay Rawat. Sanjay sir helped me staying focused on problems and provided new directions to approach them. Working with him, I have devel- oped my problem solving skills, learnt about research, about life in general. I would be thankful to him for all my life, for providing me the guidance on various matters, always motivating and boosting me with confidence, which really helped me in shaping my life. I must also thank all my lab-mates who are working or have worked earlier in CSTAR - Vijayendra, Spandan, Satwik, Charu, Teja, Ishan and Lokesh. I really enjoyed working with them in the lab. I would like to thank all my friends in IIIT, for making my stay in the campus a memorable one. -
Chapter 2: Operating-System Structures
Chapter 2: Operating-System Structures Operating System Concepts – 10th Edition Silberschatz, Galvin and Gagne ©2018 Chapter 2: Operating-System Structures Operating System Services User and Operating System-Interface System Calls System Services Linkers and Loaders Why Applications are Operating System Specific Operating-System Design and Implementation Operating System Structure Building and Booting an Operating System Operating System Debugging Operating System Concepts – 10th Edition 2.2 Silberschatz, Galvin and Gagne ©2018 Objectives Identify services provided by an operating system Illustrate how system calls are used to provide operating system services Compare and contrast monolithic, layered, microkernel, modular, and hybrid strategies for designing operating systems Illustrate the process for booting an operating system Apply tools for monitoring operating system performance Design and implement kernel modules for interacting with a Linux kernel Operating System Concepts – 10th Edition 2.3 Silberschatz, Galvin and Gagne ©2018 Operating System Services Operating systems provide an environment for execution of programs and services to programs and users One set of operating-system services provides functions that are helpful to the user: User interface - Almost all operating systems have a user interface (UI). Varies between Command-Line (CLI), Graphics User Interface (GUI), touch-screen, Batch Program execution - The system must be able to load a program into memory and to run that program, end execution, either normally or abnormally (indicating error) I/O operations - A running program may require I/O, which may involve a file or an I/O device Operating System Concepts – 10th Edition 2.4 Silberschatz, Galvin and Gagne ©2018 Operating System Services (Cont.) One set of operating-system services provides functions that are helpful to the user (Cont.): File-system manipulation - The file system is of particular interest. -
Linux-Kernel
linux-kernel #linux- kernel Table of Contents About 1 Chapter 1: Getting started with linux-kernel 2 Remarks 2 Versions 2 Examples 2 Installation or Setup 2 Download extract and enter to the kernel directory 2 Build the dependencies, compile the kernel and modules. 3 Chapter 2: Creation and usage of Kernel Threads 4 Introduction 4 Examples 4 Creation of kernel threads 4 Chapter 3: Event Tracing 6 Examples 6 Tracing I2C Events 6 Chapter 4: Fork System call 7 Examples 7 fork() system call 7 Chapter 5: How to find the right person for help. 9 Introduction 9 Examples 9 Find the "likely" maintainers for the FTDI USB serial converter 9 Chapter 6: Linux Hello World Device driver 10 Examples 10 An empty kernel module 10 Building and running the module 10 Chapter 7: Linux: Named Pipes(FIFO) 12 Examples 12 What is Named Pipe (FIFO) 12 Credits 13 About You can share this PDF with anyone you feel could benefit from it, downloaded the latest version from: linux-kernel It is an unofficial and free linux-kernel ebook created for educational purposes. All the content is extracted from Stack Overflow Documentation, which is written by many hardworking individuals at Stack Overflow. It is neither affiliated with Stack Overflow nor official linux-kernel. The content is released under Creative Commons BY-SA, and the list of contributors to each chapter are provided in the credits section at the end of this book. Images may be copyright of their respective owners unless otherwise specified. All trademarks and registered trademarks are the property of their respective company owners.