Operating Systems Overview
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Questions and Answers

What does the exec() system call do in the process lifecycle?

  • Changes the currently running program (correct)
  • Creates a new process
  • Terminates the process
  • Opens a file in read mode

    • The process returns to user mode after calling a system call.

    True

    What is created when a file is opened through the open() system call?

    An inode

    The standard library for C programming language is called ______.

    <p>libc</p> Signup and view all the answers

    Match the following file operations with their corresponding actions:

    <p>open() = Creates a file descriptor write() = Writes data to a file fork() = Creates a new process exec() = Replaces the current program in a process</p> Signup and view all the answers

    Which of the following describes the purpose of shared libraries?

    <p>To allow multiple programs to use the same code</p> Signup and view all the answers

    The write() system call switches the process to user mode.

    <p>False</p> Signup and view all the answers

    What is the initial mode when a process is created?

    <p>User mode</p> Signup and view all the answers

    What is the main purpose of lazy binding in operating systems?

    <p>To resolve function addresses at runtime</p> Signup and view all the answers

    Lazy binding resolves the address of a function at compile time.

    <p>False</p> Signup and view all the answers

    What happens when a function is called using lazy binding for the first time?

    <p>It jumps to the PLT entry, which calls the relocation resolver to find the real address.</p> Signup and view all the answers

    In lazy binding, the initial call to a shared function points to the _________ resolver code.

    <p>relocation</p> Signup and view all the answers

    Match the following components of lazy binding with their roles:

    <p>PLT = Jump to the real function address GOT = Holds addresses of shared functions Relocation Resolver = Finds real addresses of functions Call to Function = Initial jump to the PLT entry</p> Signup and view all the answers

    Which of the following statements about shared libraries is true?

    <p>Shared libraries use lazy binding to optimize function calls.</p> Signup and view all the answers

    The Global Offset Table (GOT) maintains the default addresses of all functions in shared libraries.

    <p>True</p> Signup and view all the answers

    Describe the role of the Global Offset Table (GOT) in lazy binding.

    <p>The GOT holds the addresses of the shared functions, initially pointing to the relocation resolver, which updates them later.</p> Signup and view all the answers

    The performing of _________ minimizes the need to recompile code each time a library is updated.

    <p>dynamic linking</p> Signup and view all the answers

    What does the process of deferred binding primarily enhance?

    <p>Memory efficiency</p> Signup and view all the answers

    What is the main advantage of using shared libraries?

    <p>Reduces memory usage by avoiding code duplication</p> Signup and view all the answers

    Shared libraries are fixed in memory addresses across different processes.

    <p>False</p> Signup and view all the answers

    What is the role of the dynamic linker in relation to shared libraries?

    <p>To load and link shared libraries and functions into the process' virtual address space</p> Signup and view all the answers

    Shared libraries are shared among all processes using them through __________.

    <p>memory mappings</p> Signup and view all the answers

    Match the following functions with their respective roles in the context of shared libraries:

    <p>printf() = Standard output function mmap() = Memory mapping for shared libraries dynamic linker = Loads shared libraries into memory ELF format = Executable and Linkable Format for binaries</p> Signup and view all the answers

    When does the dynamic linker resolve the address of a shared function?

    <p>At run time</p> Signup and view all the answers

    Static linking improves memory usage compared to shared libraries.

    <p>False</p> Signup and view all the answers

    What is the first action taken by an executable in UNIX systems using ELF format?

    <p>Run the linker code to load the binary in memory</p> Signup and view all the answers

    The dynamic linker is tasked with __________ shared libraries needed by the program.

    <p>loading</p> Signup and view all the answers

    Which of the following statements is true regarding shared libraries?

    <p>They can be dynamically linked at run time</p> Signup and view all the answers

    What does a process control block (PCB) represent in an operating system kernel?

    <p>The data and resources allocated to a process</p> Signup and view all the answers

    The system call kill() can be used to send a signal to terminate processes.

    <p>True</p> Signup and view all the answers

    What is the purpose of shared libraries in an operating system?

    <p>To provide reusable functions and resources for programs without needing their own copy.</p> Signup and view all the answers

    In process communication, a process can send a signal using the system call kill() with the argument _____ for stopping the process.

    <p>SIGSTOP</p> Signup and view all the answers

    Match the following terms with their descriptions:

    <p>Signal = A method for process communication and control Shared Library = Collection of code and resources accessible by multiple programs System Call = A user request to the operating system for a service Process Control Block = Data structure that contains information about a process</p> Signup and view all the answers

    What does the Procedure Linkage Table (PLT) contain?

    <p>Stubs to jump to the proper address for shared library functions</p> Signup and view all the answers

    Lazy binding resolves all relocations when the program starts.

    <p>False</p> Signup and view all the answers

    What is the purpose of the Global Offset Table (GOT)?

    <p>It contains relocations between symbols in the program and addresses in shared objects.</p> Signup and view all the answers

    Eager binding also known as __________ binding, resolves all relocations when the program starts.

    <p>immediate</p> Signup and view all the answers

    Match the following components with their descriptions:

    <p>PLT = Contains stubs for function calls to shared libraries GOT = Manages symbol address relocations Eager Binding = Resolves relocations at program start Lazy Binding = Resolves relocations when needed during program execution</p> Signup and view all the answers

    Which of the following strategies requires restructuring the GOT during program start?

    <p>Eager Binding</p> Signup and view all the answers

    The dynamic linker typically uses information in the ELF header for linking operations.

    <p>True</p> Signup and view all the answers

    What information does the ELF header primarily provide for linking operations?

    <p>It provides the address of the PLT and GOT, and other related metadata.</p> Signup and view all the answers

    When a shared library function is called, it jumps to the corresponding ______ entry that directs it to the address in the GOT.

    <p>PLT</p> Signup and view all the answers

    Which of the following best describes the initial action of the dynamic linker?

    <p>It loads shared libraries into memory and resolves addresses.</p> Signup and view all the answers

    Study Notes

    File Manipulation Process

    • Process creation involves forking from a parent process, copying its PCB.
    • The exec() system call is used to replace the current process image with a new program.
    • Default file descriptors opened are stdin, stdout, and stderr.
    • The open() system call is made to access "foo.txt" in write-only mode, transitioning to supervisor mode.
    • An inode is created which allocates necessary blocks on the device.
    • A file descriptor pointing to the inode is formed, initialized with mode and offset 0, and linked to the file table in the PCB.
    • Following the write operation through write(), the kernel accesses the file descriptor and locates the appropriate block for data writing.

    Shared Libraries

    • Shared libraries prevent code duplication in memory by allowing multiple programs to use the same library simultaneously.
    • Libraries like libc for C are common, where static linking would lead to wasted memory across multiple binaries.
    • Memory mappings (via mmap()) facilitate shared usage of libraries.

    Function Resolution in Shared Libraries

    • The address of a shared function can differ across processes due to individual mappings in their virtual address spaces.
    • Dynamic linkers facilitate the loading and linking of shared libraries and functions at runtime, not at compile time.

    Dynamic Linker Operations

    • The dynamic linker is essential for loading the binary into memory, setting up the memory layout, and loading necessary shared libraries during program execution.
    • Example shows how a program using printf() translates to assembly code that accesses a shared library.

    Lazy Binding

    • Lazy binding resolves function addresses only upon the first call, utilizing the Procedure Linkage Table (PLT) and the Global Offset Table (GOT).
    • The initial call routes through the relocation resolver, which updates the GOT for subsequent calls to directly access the correct function address.
    • Linking operations rely on ELF header information, identifying necessary symbols and relocation data.

    Eager Binding

    • Eager binding resolves all relocations when a program starts, modifying entries in the GOT for functions and variables.
    • On function calls, the program jumps to the corresponding entry in PLT leading directly to the address in the GOT.

    User-Kernel Interactions

    • A process is defined within the kernel by its process control block (PCB).
    • User-space programs interact with the kernel through integer values for system calls, virtual addresses for memory management, and file descriptor tables for file operations.

    Signal Handling Example

    • Process 1 can send a STOP signal to process 2 using the kill() system call, which involves transitioning to supervisor mode and setting appropriate bits in the pending signals of process 2.

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    Description

    Explore the fundamental concepts of operating systems and file manipulation through a detailed example of process creation and management. This quiz assesses your understanding of how processes interact with files and the system. Test your knowledge of these essential software components.

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