Operating Systems Overview

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 ______.

libc Signup and view all the answers

Match the following file operations with their corresponding actions:

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

Which of the following describes the purpose of shared libraries?

To allow multiple programs to use the same code Signup and view all the answers

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

False Signup and view all the answers

What is the initial mode when a process is created?

User mode Signup and view all the answers

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

To resolve function addresses at runtime Signup and view all the answers

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

False Signup and view all the answers

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

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

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

relocation Signup and view all the answers

Match the following components of lazy binding with their roles:

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 Signup and view all the answers

Which of the following statements about shared libraries is true?

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

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

True Signup and view all the answers

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

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

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

dynamic linking Signup and view all the answers

What does the process of deferred binding primarily enhance?

Memory efficiency Signup and view all the answers

What is the main advantage of using shared libraries?

Reduces memory usage by avoiding code duplication Signup and view all the answers

Shared libraries are fixed in memory addresses across different processes.

False Signup and view all the answers

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

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

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

memory mappings Signup and view all the answers

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

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 Signup and view all the answers

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

At run time Signup and view all the answers

Static linking improves memory usage compared to shared libraries.

False Signup and view all the answers

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

Run the linker code to load the binary in memory Signup and view all the answers

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

loading Signup and view all the answers

Which of the following statements is true regarding shared libraries?

They can be dynamically linked at run time Signup and view all the answers

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

The data and resources allocated to a process Signup and view all the answers

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

True Signup and view all the answers

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

To provide reusable functions and resources for programs without needing their own copy. 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.

SIGSTOP Signup and view all the answers

Match the following terms with their descriptions:

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 Signup and view all the answers

What does the Procedure Linkage Table (PLT) contain?

Stubs to jump to the proper address for shared library functions Signup and view all the answers

Lazy binding resolves all relocations when the program starts.

False Signup and view all the answers

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

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

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

immediate Signup and view all the answers

Match the following components with their descriptions:

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 Signup and view all the answers

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

Eager Binding Signup and view all the answers

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

True Signup and view all the answers

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

It provides the address of the PLT and GOT, and other related metadata. 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.

PLT Signup and view all the answers

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

It loads shared libraries into memory and resolves addresses. 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.

Operating Systems Overview

Questions and Answers

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

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

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

The standard library for C programming language is called ______.

Match the following file operations with their corresponding actions:

Which of the following describes the purpose of shared libraries?

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

What is the initial mode when a process is created?

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

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

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

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

Match the following components of lazy binding with their roles:

Which of the following statements about shared libraries is true?

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

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

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

What does the process of deferred binding primarily enhance?

What is the main advantage of using shared libraries?

Shared libraries are fixed in memory addresses across different processes.

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

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

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

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

Static linking improves memory usage compared to shared libraries.

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

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

Which of the following statements is true regarding shared libraries?

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

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

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

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

Match the following terms with their descriptions:

What does the Procedure Linkage Table (PLT) contain?

Lazy binding resolves all relocations when the program starts.

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

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

Match the following components with their descriptions:

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

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

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

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

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

Study Notes

File Manipulation Process

Shared Libraries

Function Resolution in Shared Libraries

Dynamic Linker Operations

Lazy Binding

Eager Binding

User-Kernel Interactions

Signal Handling Example

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Description

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