CSE 421 / 521 example explanation

Time:2021-10-12

Programming Assignment – 2
CSE 421/521 – Operating Systems
Due: April 5
th and April 19
th @11:59 pm, 2019

  1. Preparation
    Before beginning your work, please read the following carefully:
    ● Chapters 8-9 from Silberschatz (9
    th edition)
    ● Lecture slides on Memory and Virtual Memory
    ● Pintos Introduction
    ● Pintos Reference Guide
    ● Complete Pintos Documentation (PDF file) — for reference only
  2. Task: Implement the User Programs of Pintos OS
    In this project, you are asked to perform “kernel” level programming of the “User
    Programs” component in the Pintos operating system. The base code already supports loading
    and running user programs, but no I/O or interactivity is possible. In this project, you will enable
    programs to interact with the OS via system calls.
    Before beginning this assignment, make sure you read these sections from Pintos
    Reference Guide: section A.1 Pintos Loading, A.2 Threads, A.3 Synchronization, A.4 Interrupt
    Handling, A.5 Memory Allocation, A.6 Virtual Addresses, and Appendix E (Debugging Tools).
    Page: 1/19
  3. Setting Up The Pintos Environment
    Project-2 does not depend on project-1. No code from project-1 is required for this
    assignment. So, we suggest that you fetch a clean copy of the Pintos source code.
    We have prepared a Virtual Machine image of Pintos which will make the
    installation/configuration process much simpler for you. This will enable you to develop your
    pintos project on any Linux, Windows, or Mac system (i.e. your own machine) without much
    hassle. You can also download the VM image from:
    https://buffalo.box.com/s/erd…
    http://ftp.cse.buffalo.edu/CS…
    After downloading the file, verify the integrity of the file by comparing the md5 hash of the
    downloaded file with:
    ecf501c3494f741f6d56f7ebe6064beb
    You will need VirtualBox software for your host OS to run this VM. You can download
    VirtualBox at the following link:
    https://www.virtualbox.org/wi…
    For the detailed instruction on how to setup this VM on your host OS, please see the
    “Environment Setup” on Piazza:
    http://www.piazza.com/class_p…
    In VirtualBox software, from the File menu, choose “Import Appliance” and point to the
    downloaded “UB-pintos.ova”. You do not need to change any other settings for this procedure.
    Choose UB-Pintos from the left pane, and click on “Start”, your virtual machine should now
    boot. Here is the login information if needed:
    Username: os-class
    Password: os-class
    To learn how to run, debug and test Pintos code, please read the Pintos Introduction.
    Page: 2/19
  4. Implementation of the Project
    You will be working primarily in the “userprog” directory of the source tree for this
    assignment. Compilation should be done in the “userprog” directory.
    4.1 Background
    Up to now, all of the code you have run under Pintos has been part of the operating
    system kernel. This means, for example, that all the test code from the last assignment ran as part
    of the kernel, with full access to privileged parts of the system. Once we start running user
    programs on top of the operating system, this is no longer true. This project deals with the
    consequences.
    We allow more than one process to run at a time. Each process has one thread
    (multi-threaded processes are not supported). User programs are written under the illusion that
    they have the entire machine. This means that when you load and run multiple processes at a
    time, you must manage memory, scheduling, and other state correctly to maintain this illusion.
    In the previous project, we compiled our test code directly into your kernel, so we had to
    require specific function interfaces within the kernel. From now on, we will test your operating
    system by running user programs. This gives you much greater freedom. You must make sure that
    the user program interface meets the specifications described here, but given that constraint you
    are free to restructure or rewrite kernel code however you wish.
    4.2 Source Files
    The easiest way to get an overview of the programming you will be doing is to simply go
    over each part you’ll be working with. In `userprog’, you’ll find a small number of files, but here is
    where the bulk of your work will be:
    `process.c’
    `process.h’
    Loads ELF binaries and starts processes.
    `pagedir.c’
    `pagedir.h’
    A simple manager for 80×86 hardware page tables. Although you probably won’t want to
    modify this code for this project, you may want to call some of its functions. See Section 4.1.2.3
    [Page Tables] from Pintos Manual, for more information.
    `syscall.c’
    `syscall.h’
    Whenever a user process wants to access some kernel functionality, it invokes a system
    call. This is a skeleton system call handler. Currently, it just prints a message and terminates the
    user process. In part 2 of this project you will add code to do everything else needed by system
    calls.
    `exception.c’
    Page: 3/19
    `exception.h’
    When a user process performs a privileged or prohibited operation, it traps into the kernel
    as an “exception” or “fault.” These files handle exceptions. Currently all exceptions simply print
    1
    a message and terminate the process. Some, but not all, solutions to project 2 require modifying
    page_fault() in this file.
    `gdt.c’
    `gdt.h’
    The 80×86 is a segmented architecture. The Global Descriptor Table (GDT) is a table that
    describes the segments in use. These files set up the GDT. You should not need to modify these
    files for any of the projects. You can read the code if you’re interested in how the GDT works.
    `tss.c’
    `tss.h’
    The Task-State Segment (TSS) is used for 80×86 architectural task switching. Pintos uses
    the TSS only for switching stacks when a user process enters an interrupt handler, as does Linux.
    You should not need to modify these files for any of the projects. You can read the code if you’re
    interested in how the TSS works.
    4.3 Using the File System
    You will need to interface to the file system code for this project, because user programs
    are loaded from the file system and many of the system calls you must implement deal with the
    file system. However, the focus of this project is not the file system, so we have provided a
    simple but complete file system in the `filesys’ directory. You will want to look over the
    filesys.h' and file.h’ interfaces to understand how to use the file system, and especially its many
    limitations.
    There is no need to modify the file system code for this project, and so we recommend
    that you do not. Working on the file system is likely to distract you from this project’s focus.
    You will have to tolerate the following limitations of the file system:
    ● No internal synchronization. Concurrent accesses will interfere with one another. You
    should use synchronization to ensure that only one process at a time is executing file
    system code.
    ● File size is fixed at creation time. The root directory is represented as a file, so the
    number of files that may be created is also limited.
    ● File data is allocated as a single extent, that is, data in a single file must occupy a
    contiguous range of sectors on disk. External fragmentation can therefore become a
    serious problem as a file system is used over time.
    ● No subdirectories.
    ● File names are limited to 14 characters.
    ● A system crash mid-operation may corrupt the disk in a way that cannot be repaired
  5. We will treat these terms as synonyms. There is no standard distinction between them, although Intel processor
    manuals make a minor distinction between them on 80×86.
    Page: 4/19
    automatically. There is no file system repair tool anyway.
    One important feature is included:
    ● Unix-like semantics for filesys_remove() are implemented. That is, if a file is open when
    it is removed, its blocks are not deallocated and it may still be accessed by any threads
    that have it open, until the last one closes it. See Section 3.4.2 FAQ [Removing an Open
    File] from Pintos Manual for more information.
    You need to be able to create a simulated disk with a file system partition. The
    pintos-mkdisk program provides this functionality. From the `userprog/build’ directory, execute
    pintos-mkdisk filesys.dsk –filesys-size=2. This command creates a simulated disk named
    `filesys.dsk’ that contains a 2 MB Pintos file system partition. Then format the file system
    partition by passing -f -q' on the kernel's command line: pintos -f -q. The -f’ option causes the
    file system to be formatted, and `-q’ causes Pintos to exit as soon as the format is done.
    You’ll need a way to copy files in and out of the simulated file system. The pintos `-p’
    (“put”) and -g' (“get") options do this. To copy file’ into the Pintos file system, use the command
    pintos -p file -- -q'. (The –‘ is needed because `-p’ is for the pintos script, not for the simulated
    kernel.) To copy it to the Pintos file system under the name newname', add -a newname’: `pintos
    -p file -a newname — -q’. The commands for copying files out of a VM are similar, but substitute
    -g' for -p’.
    Incidentally, these commands work by passing special commands extract and append on
    the kernel’s command line and copying to and from a special simulated “scratch” partition. If
    you’re very curious, you can look at the pintos script as well as `filesys/fsutil.c’ to learn the
    implementation details.
    Here’s a summary of how to create a disk with a file system partition, format the file
    system, copy the echo program into the new disk, and then run echo, passing argument x.
    (Argument passing won’t work until you implemented it.) It assumes that you’ve already built the
    examples in examples' and that the current directory is userprog/build’:
    pintos-mkdisk filesys.dsk –filesys-size=2
    pintos -f -q
    pintos -p ../../examples/echo -a echo — -q
    pintos -q run ‘echo x’
    The three final steps can actually be combined into a single command:
    pintos-mkdisk filesys.dsk –filesys-size=2
    pintos -p ../../examples/echo -a echo — -f -q run ‘echo x’
    If you don’t want to keep the file system disk around for later use or inspection, you can
    even combine all four steps into a single command. The –filesys-size=n option creates a
    temporary file system partition approximately n megabytes in size just for the duration of the
    pintos run. The Pintos automatic test suite makes extensive use of this syntax:
    pintos –filesys-size=2 -p ../../examples/echo -a echo — -f -q run ‘echo x’
    You can delete a file from the Pintos file system using the rm file kernel action, e.g.
    pintos -q rm file. Also, ls lists the files in the file system and cat file prints a file’s contents to the
    display.
    Page: 5/19
    4.4 How User Programs Work
    Pintos can run normal C programs, as long as they fit into memory and use only the
    system calls you implement. Notably, malloc() cannot be implemented because none of the
    system calls required for this project allow for memory allocation. Pintos also can’t run programs
    that use floating point operations, since the kernel doesn’t save and restore the processor’s
    floating-point unit when switching threads.
    The src/examples' directory contains a few sample user programs. The Makefile’ in this
    directory compiles the provided examples, and you can edit it to compile your own programs as
    well. Some of the example programs will only work once projects 3 or 4 have been implemented.
    Pintos can load ELF executables with the loader provided for you in `userprog/process.c’.
    ELF is a file format used by Linux, Solaris, and many other operating systems for object files,
    shared libraries, and executables. You can actually use any compiler and linker that output 80×86
    ELF executables to produce programs for Pintos. (We’ve provided compilers and linkers that
    should do just fine.)
    You should realize immediately that, until you copy a test program to the simulated file
    system, Pintos will be unable to do useful work. You won’t be able to do interesting things until
    you copy a variety of programs to the file system. You might want to create a clean reference file
    system disk and copy that over whenever you trash your `filesys.dsk’ beyond a useful state, which
    may happen occasionally while debugging.
    4.5 Virtual Memory Layout
    Virtual memory in Pintos is divided into two regions: user virtual memory and kernel
    virtual memory. User virtual memory ranges from virtual address 0 up to PHYS_BASE, which is
    defined in `threads/vaddr.h’ and defaults to 0xc0000000 (3 GB). Kernel virtual memory occupies
    the rest of the virtual address space, from PHYS_BASE up to 4 GB.
    User virtual memory is per-process. When the kernel switches from one process to
    another, it also switches user virtual address spaces by changing the processor’s page directory
    base register (see pagedir_activate() in `userprog/pagedir.c’). struct thread contains a pointer to a
    process’s page table.
    Kernel virtual memory is global. It is always mapped the same way, regardless of what
    user process or kernel thread is running. In Pintos, kernel virtual memory is mapped one-to-one to
    physical memory, starting at PHYS_BASE. That is, virtual address PHYS_BASE accesses
    physical address 0, virtual address PHYS_BASE + 0x1234 accesses physical address 0x1234, and
    so on up to the size of the machine’s physical memory.
    A user program can only access its own user virtual memory. An attempt to access kernel
    virtual memory causes a page fault, handled by page_fault() in `userprog/exception.c’, and the
    process will be terminated. Kernel threads can access both kernel virtual memory and, if a user
    process is running, the user virtual memory of the running process. However, even in the kernel,
    an attempt to access memory at an unmapped user virtual address will cause a page fault.
    Page: 6/19
    4.6 Typical Memory Layout
    Conceptually, each process is free to lay out its own user virtual memory however it
    chooses. In practice, user virtual memory is laid out like this:
    In this project, the user stack is fixed in size. Traditionally, the size of the uninitialized
    data segment can be adjusted with a system call, but you will not have to implement this.
    The code segment in Pintos starts at user virtual address 0x08048000, approximately 128
    MB from the bottom of the address space. This value is specified in [SysV-i386] and has no deep
    significance.
    The linker sets the layout of a user program in memory, as directed by a “linker script”
    that tells it the names and locations of the various program segments. You can learn more about
    linker scripts by reading the \Scripts” chapter in the linker manual, accessible via `info ld’.
    To view the layout of a particular executable, run objdump (80×86) or i386-elf-objdump
    (SPARC) with the `-p’ option.
    Page: 7/19
    4.7 Accessing User Memory
    As part of a system call, the kernel must often access memory through pointers provided
    by a user program. The kernel must be very careful about doing so, because the user can pass a
    null pointer, a pointer to unmapped virtual memory, or a pointer to kernel virtual address space
    (above PHYS_BASE). All of these types of invalid pointers must be rejected without harm to the
    kernel or other running processes, by terminating the offending process and freeing its resources.
    There are at least two reasonable ways to do this correctly. The first method is to verify
    the validity of a user-provided pointer, then dereference it. If you choose this route, you’ll want to
    look at the functions in userprog/pagedir.c' and in threads/vaddr.h’. This is the simplest way to
    handle user memory access.
    The second method is to check only that a user pointer points below PHYS_BASE, then
    dereference it. An invalid user pointer will cause a \page fault” that you can handle by modifying
    the code for page_fault() in `userprog/exception.c’. This technique is normally faster because it
    takes advantage of the processor’s MMU, so it tends to be used in real kernels (including Linux).
    In either case, you need to make sure not to “leak” resources. For example, suppose that
    your system call has acquired a lock or allocated memory with malloc(). If you encounter an
    invalid user pointer afterward, you must still be sure to release the lock or free the page of
    memory. If you choose to verify user pointers before dereferencing them, this should be
    straightforward. It’s more difficult to handle if an invalid pointer causes a page fault, because
    there’s no way to return an error code from a memory access. Therefore, for those who want to try
    the latter technique, we’ll provide a little bit of helpful code:
    /* Reads a byte at user virtual address UADDR.
    UADDR must be below PHYS_BASE.
    Returns the byte value if successful, -1 if a segfault
    occurred. */
    static int
    get_user (const uint8_t *uaddr)
    {
    int result;
    asm (“movl $1f, %0; movzbl %1, %0; 1:”
    : “=&a” (result) : “m” (*uaddr));
    return result;
    }
    /* Writes BYTE to user address UDST.
    UDST must be below PHYS_BASE.
    Returns true if successful, false if a segfault occurred.
    */
    static bool
    put_user (uint8_t *udst, uint8_t byte)
    {
    int error_code;
    asm (“movl $1f, %0; movb %b2, %1; 1:”
    Page: 8/19
    : “=&a” (error_code), “=m” (*udst) : “q” (byte));
    return error_code != -1;
    }
    4.8 Suggested Order of Implementation
    We suggest first implementing the following, which can happen in parallel:
    ● Argument passing (see Section 3.3.3 [Argument Passing] from Pintos Manual). Every
    user program will page fault immediately until argument passing is implemented.
    For now, you may simply wish to change
    *esp = PHYS_BASE;
    to
    *esp = PHYS_BASE – 12;
    in setup_stack(). That will work for any test program that doesn’t examine its arguments, although
    its name will be printed as (null). Until you implement argument passing, you should
    only run programs without passing command-line arguments. Attempting to pass
    arguments to a program will include those arguments in the name of the program, which
    will probably fail.
    ● User memory access (see Section 3.1.5 [Accessing User Memory] from Pintos Manual).
    All system calls need to read user memory. Few system calls need to write to user
    memory.
    ● System call infrastructure (see Section 3.3.4 [System Calls] from Pintos Manual).
    Implement enough code to read the system call number from the user stack and dispatch
    to a handler based on it.
    ● The exit system call. Every user program that finishes in the normal way calls exit. Even
    a program that returns from main() calls exit indirectly (see _start() in `lib/user/entry.c’).
    ● The write system call for writing to fd 1, the system console. All of our test programs
    write to the console (the user process version of printf() is implemented this way), so they
    will all malfunction until write is available.
    ● For now, change process_wait() to an infinite loop (one that waits forever). The provided
    implementation returns immediately, so Pintos will power off before any processes
    actually get to run. You will eventually need to provide a correct implementation.
    After the above are implemented, user processes should work minimally. At the very least, they
    can write to the console and exit correctly. You can then refine your implementation so that some
    of the tests start to pass.
    Page: 9/19
    4.9 Requirements
    4.9.1 Process Termination Messages
    Whenever a user process terminates, because it called exit or for any other reason, print
    the process’s name and exit code, formatted as if printed by printf (“%s: exit(%d)\n”, …);. The
    name printed should be the full name passed to process_execute(), omitting command-line
    arguments. Do not print these messages when a kernel thread that is not a user process terminates,
    or when the halt system call is invoked. The message is optional when a process fails to load.
    Aside from this, don’t print any other messages that Pintos as provided doesn’t already
    print. You may _nd extra messages useful during debugging, but they will confuse the grading
    scripts and thus lower your score.
    4.9.2 Argument Passing
    Currently, process_execute() does not support passing arguments to new processes.
    Implement this functionality, by extending process_execute() so that instead of simply taking a
    program file name as its argument, it divides it into words at spaces. The _rst word is the program
    name, the second word is the _rst argument, and so on. That is, process_execute(“grep foo bar”)
    should run grep passing two arguments foo and bar.
    Within a command line, multiple spaces are equivalent to a single space, so that
    process_execute(“grep foo bar”) is equivalent to our original example. You can impose a
    reasonable limit on the length of the command line arguments. For example, you could limit the
    arguments to those that will _t in a single page (4 kB). (There is an unrelated limit of 128 bytes on
    command-line arguments that the pintos utility can pass to the kernel.)
    You can parse argument strings any way you like. If you’re lost, look at strtok_r(),
    prototyped in lib/string.h' and implemented with thorough comments in lib/string.c’. You can
    _nd more about it by looking at the man page (run man strtok_r at the prompt).
    See Section 3.5.1 [Program Startup Details] from Pintos Manual, for information on
    exactly how you need to set up the stack.
    Page: 10/19
    4.9.3 System Calls
    Implement the system call handler in `userprog/syscall.c’. The skeleton implementation
    we provide \handles” system calls by terminating the process. It will need to retrieve the system
    call number, then any system call arguments, and carry out appropriate actions.
    Implement the following system calls. The prototypes listed are those seen by a user
    program that includes lib/user/syscall.h'. (This header, and all others in lib/user’, are for use by
    user programs only.) System call numbers for each system call are defined in `lib/syscall-nr.h’:
    [System Call] void halt (void)
    Terminates Pintos by calling shutdown_power_off() (declared in `devices/shutdown.h’).
    This should be seldom used, because you lose some information about possible deadlock
    situations, etc.
    [System Call] void exit (int status)
    Terminates the current user program, returning status to the kernel. If the process’s parent
    waits for it (see below), this is the status that will be returned. Conventionally, a status of 0
    indicates success and nonzero values indicate errors.
    [System Call] pid_t exec (const char *cmd_line)
    Runs the executable whose name is given in cmd line, passing any given arguments, and
    returns the new process’s program id (pid). Must return pid -1, which otherwise should not be a
    valid pid, if the program cannot load or run for any reason. Thus, the parent process cannot return
    from the exec until it knows whether the child process successfully loaded its executable. You
    must use appropriate synchronization to ensure this.
    [System Call] int wait (pid t pid)
    Waits for a child process pid and retrieves the child’s exit status. If pid is still alive, waits
    until it terminates. Then, returns the status that pid passed to exit. If pid did not call exit(), but was
    terminated by the kernel (e.g. killed due to an exception), wait(pid) must return -1. It is perfectly
    legal for a parent process to wait for child processes that have already terminated by the time the
    parent calls wait, but the kernel must still allow the parent to retrieve its child’s exit status, or
    learn that the child was terminated by the kernel. wait must fail and return -1 immediately if any
    of the following conditions is true:
    ● pid does not refer to a direct child of the calling process. pid is a direct child of the
    calling process if and only if the calling process received pid as a return value from a
    successful call to exec.
    Note that children are not inherited: if A spawns child B and B spawns child process C,
    then A cannot wait for C, even if B is dead. A call to wait(C) by process A must fail. Similarly,
    orphaned processes are not assigned to a new parent if their parent process exits before they do.
    ● The process that calls wait has already called wait on pid. That is, a process may wait
    for any given child at most once.
    Processes may spawn any number of children, wait for them in any order, and may even
    exit without having waited for some or all of their children. Your design should consider all the
    ways in which waits can occur. All of a process’s resources, including its struct thread, must be
    freed whether its parent ever waits for it or not, and regardless of whether the child exits before or
    Page: 11/19
    after its parent.
    You must ensure that Pintos does not terminate until the initial process exits. The
    supplied Pintos code tries to do this by calling process_wait() (in `userprog/process.c’) from
    main() (in `threads/init.c’). We suggest that you implement process_wait() according to the
    comment at the top of the function and then implement the wait system call in terms of
    process_wait(). Implementing this system call requires considerably more work than any of the
    rest.
    [System Call] bool create (const char *file, unsigned initial_size)
    Creates a new file called ‘file’ initially initial_size bytes in size. Returns true if
    successful, false otherwise. Creating a new file does not open it: opening the new file is a separate
    operation which would require a open system call.
    [System Call] bool remove (const char *file)
    Opens the file called `file’. Returns a nonnegative integer handle called a “file descriptor”
    (fd), or -1 if the file could not be opened. File descriptors numbered 0 and 1 are reserved for the
    console: fd 0 (STDIN_FILENO) is standard input, fd 1 (STDOUT_FILENO) is standard output.
    The open system call will never return either of these file descriptors, which are valid as system
    call arguments only as explicitly described below.
    Each process has an independent set of file descriptors. File descriptors are not inherited
    by child processes. When a single file is opened more than once, whether by a single process or
    different processes, each open returns a new file descriptor. Different file descriptors for a single
    file are closed independently in separate calls to close and they do not share a file position.
    [System Call] int filesize (int fd)
    Returns the size, in bytes, of the file open as fd.
    [System Call] int read (int fd, void *buffer, unsigned size)
    Reads size bytes from the file open as fd into buffer. Returns the number of bytes actually
    read (0 at end of file), or -1 if the file could not be read (due to a condition other than end of file).
    Fd 0 reads from the keyboard using input_getc().
    [System Call] int write (int fd, const void *buffer, unsigned size)
    Writes size bytes from buffer to the open file fd. Returns the number of bytes actually
    written, which may be less than size if some bytes could not be written.
    Writing past end-of-file would normally extend the file, but file growth is not
    implemented by the basic file system. The expected behavior is to write as many bytes as possible
    up to end-of-file and return the actual number written, or 0 if no bytes could be written at all.
    Fd 1 writes to the console. Your code to write to the console should write all of buffer in
    one call to putbuf(), at least as long as size is not bigger than a few hundred bytes. (It is
    reasonable to break up larger buffers.) Otherwise, lines of text output by different processes may
    end up interleaved on the console, confusing both human readers and our grading scripts.
    [System Call] void seek (int fd, unsigned position)
    Changes the next byte to be read or written in open file fd to position, expressed in bytes
    from the beginning of the file. (Thus, a position of 0 is the file’s start.) A seek past the current end
    Page: 12/19
    of a file is not an error. A later read obtains 0 bytes, indicating end of file. A later write extends
    the file, filling any unwritten gap with zeros. (However, in Pintos files have a fixed length by
    default, so writes past end of file will return an error.) These semantics are implemented in the
    file system and do not require any special effort in system call implementation.
    [System Call] unsigned tell (int fd)
    Returns the position of the next byte to be read or written in open file fd, expressed in
    bytes from the beginning of the file.
    [System Call] void close (int fd)
    Closes file descriptor fd. Exiting or terminating a process implicitly closes all its open file
    descriptors, as if by calling this function for each one.
    The file defines other syscalls, but you can ignore them for this project.
    To implement syscalls, you need to provide ways to read and write data in user virtual
    address space. You need this ability before you can even obtain the system call number, because
    the system call number is on the user’s stack in the user’s virtual address space. This can be a bit
    tricky: what if the user provides an invalid pointer, a pointer into kernel memory, or a block
    partially in one of those regions? You should handle these cases by terminating the user process.
    We recommend writing and testing this code before implementing any other system call
    functionality. See Section 3.1.5 [Accessing User Memory] from Pintos Manual, for more
    information.
    You must synchronize system calls so that any number of user processes can make them
    at once. In particular, it is not safe to call into the file system code provided in the `filesys’
    directory from multiple threads at once. Your system call implementation must treat the file
    system code as a critical section. Don’t forget that process_execute() also accesses files. For now,
    we recommend against modifying code in the `filesys’ directory.
    We have provided you a user-level function for each system call in `lib/user/syscall.c’.
    These provide a way for user processes to invoke each system call from a C program. Each uses a
    little inline assembly code to invoke the system call and (if appropriate) returns the system call’s
    return value.
    When you’re done with this part, and forevermore, Pintos should be bulletproof. Nothing
    that a user program can do should ever cause the OS to crash, panic, fail an assertion, or
    otherwise malfunction. It is important to emphasize this point: our tests will try to break your
    system calls in many, many ways. You need to think of all the corner cases and handle them. The
    sole way a user program should be able to cause the OS to halt is by invoking the halt system call.
    If a system call is passed an invalid argument, acceptable options include returning an
    error value (for those calls that return a value), returning an undefined value, or terminating the
    process.
    See Section 3.5.2 [System Call Details] from Pintos Manual, for details on how system
    calls work.
    4.9.4 Denying Writes to Executables
    Add code to deny writes to files in use as executables. Many OSes do this because of the
    Page: 13/19
    unpredictable results if a process tried to run code that was in the midst of being changed on disk.
    You can use file_deny_write() to prevent writes to an open file. Calling
    file_allow_write() on the file will re-enable them (unless the file is denied writes by another
    opener).
    Closing a file will also re-enable writes. Thus, to deny writes to a process’s executable,
    you must keep it open as long as the process is still running. Please also read Section 3.4 [FAQ]
    and Section 3.5 [80×86 Calling Convention] from Pintos manual for more information.
  6. Testing
    Your project grade will be based on our tests. Each project has several tests, each of
    which has a name beginning with “tests”. To completely test your submission, invoke “make
    check” from the project “build” directory. This will build and run each test and print a “pass” or
    “fail” message for each one. When a test fails, make check also prints some details of the reason
    for failure. After running all the tests, make check also prints a summary of the test results.
    You can also run individual tests one at a time. A given test t writes its output to
    “t.output”, then a script scores the output as “pass” or “fail” and writes the verdict to “t.result”. To
    run and grade a single test, make the “.result” file explicitly from the “build” directory, e.g. make
    tests/userprog/args-none.result. If make says that the test result is up-to-date, but
    you want to re-run it anyway, either run make clean or delete the “.output” file by hand.
    By default, each test provides feedback only at completion, not during its run. If you
    prefer, you can observe the progress of each test by specifying “VERBOSE=1” on the make
    command line, as in make check VERBOSE=1. You can also provide arbitrary options to the
    pintos run by the tests with “PINTOSOPTS=’…’”, e.g. make check PINTOSOPTS=’-j 1′ to select a
    jitter value of 1 (see Section 1.1.4 [Debugging versus Testing] from Pintos Manual).
    All of the tests and related files are in “pintos/src/tests”.
    Page: 14/19
  7. Design Document
    A copy of the Project 1 Design Document (userprog.tmpl) can be found here and
    also inside pintos/doc/. Copy the userprog.tmpl file to userprog.txt for your submission.
    Leave the header as it is. Change the “FirstName LastName mailto:[email protected]” into

    your corresponding team members details.
    CS 140
    PROJECT 2: USER PROGRAMS
    DESIGN DOCUMENT

    —- GROUP —-

    Fill in the names and email addresses of your group members.
    FirstName LastName mailto:[email protected]
    FirstName LastName mailto:[email protected]
    FirstName LastName mailto:[email protected]
    —- PRELIMINARIES —-
    If you have any preliminary comments on your submission, notes for the
    TAs, or extra credit, please give them here.
    Please cite any offline or online sources you consulted while
    preparing your submission, other than the Pintos documentation, course
    text, lecture notes, and course staff.
    We recommend that you read the design document template before you start working
    on the project. See section D. Project Documentation, for a sample design document that goes
    along with a fictitious project. You will need to decide and describe the main data structures,
    algorithms, and synchronization mechanisms that you are using / planning to use for each
    component of the project.
    Page: 15/19

  8. Grading
    The grading of the project will be done according to the following rubric :
    ● (108 points) A completely working system call implementation that passes all twenty eight
    (28) tests.
    ● (88 points) A fully code for robustness of system calls that passes all thirty-four (34) tests.
    ● (1 point) A working functionality of features that VM might break that passes one (1) test.
    ● (30 points) Passing the functionalities of the base system, passing all thirteen (13) tests.
    Run “make check” and “make grade” to see how many total points you receives from
    implementation (out of 227) and what is the grade.
    Functionality of system calls (tests/userprog/Rubric.functionality):
    3/ 3 tests/userprog/args-none
    3/ 3 tests/userprog/args-single
    3/ 3 tests/userprog/args-multiple
    3/ 3 tests/userprog/args-many
    3/ 3 tests/userprog/args-dbl-space
    3/ 3 tests/userprog/create-empty
    3/ 3 tests/userprog/create-long
    3/ 3 tests/userprog/create-normal
    3/ 3 tests/userprog/create-exists
    3/ 3 tests/userprog/open-missing
    3/ 3 tests/userprog/open-normal
    3/ 3 tests/userprog/open-twice
    3/ 3 tests/userprog/read-normal
    3/ 3 tests/userprog/read-zero
    3/ 3 tests/userprog/write-normal
    3/ 3 tests/userprog/write-zero
    3/ 3 tests/userprog/close-normal
    5/ 5 tests/userprog/exec-once
    5/ 5 tests/userprog/exec-multiple
    5/ 5 tests/userprog/exec-arg
    5/ 5 tests/userprog/wait-simple
    5/ 5 tests/userprog/wait-twice
    5/ 5 tests/userprog/exit
    3/ 3 tests/userprog/halt
    15/15 tests/userprog/multi-recurse
    3/ 3 tests/userprog/rox-simple
    3/ 3 tests/userprog/rox-child
    3/ 3 tests/userprog/rox-multichild
    Page: 16/19
    Robustness of system calls (tests/userprog/Rubric.robustness):
    2/ 2 tests/userprog/close-stdin
    2/ 2 tests/userprog/close-stdout
    2/ 2 tests/userprog/close-bad-fd
    2/ 2 tests/userprog/close-twice
    2/ 2 tests/userprog/read-bad-fd
    2/ 2 tests/userprog/read-stdout
    2/ 2 tests/userprog/write-bad-fd
    2/ 2 tests/userprog/write-stdin
    2/ 2 tests/userprog/multi-child-fd
    3/ 3 tests/userprog/create-bad-ptr
    3/ 3 tests/userprog/exec-bad-ptr
    3/ 3 tests/userprog/open-bad-ptr
    3/ 3 tests/userprog/read-bad-ptr
    3/ 3 tests/userprog/write-bad-ptr
    3/ 3 tests/userprog/create-bound
    3/ 3 tests/userprog/open-boundary
    3/ 3 tests/userprog/read-boundary
    3/ 3 tests/userprog/write-boundary
    2/ 2 tests/userprog/create-null
    2/ 2 tests/userprog/open-null
    2/ 2 tests/userprog/open-empty
    3/ 3 tests/userprog/sc-bad-arg
    3/ 3 tests/userprog/sc-bad-sp
    5/ 5 tests/userprog/sc-boundary
    5/ 5 tests/userprog/sc-boundary-2
    5/ 5 tests/userprog/exec-missing
    5/ 5 tests/userprog/wait-bad-pid
    5/ 5 tests/userprog/wait-killed
    1/ 1 tests/userprog/bad-read
    1/ 1 tests/userprog/bad-write
    1/ 1 tests/userprog/bad-jump
    1/ 1 tests/userprog/bad-read2
    1/ 1 tests/userprog/bad-write2
    1/ 1 tests/userprog/bad-jump2
    Functionality of features that VM might break (tests/userprog/no-vm/Rubric):
    1/ 1 tests/userprog/no-vm/multi-oom
    Functionality of base file system (tests/filesys/base/Rubric):
    Page: 17/19
    1/ 1 tests/filesys/base/sm-create
    2/ 2 tests/filesys/base/sm-full
    2/ 2 tests/filesys/base/sm-random
    2/ 2 tests/filesys/base/sm-seq-block
    3/ 3 tests/filesys/base/sm-seq-random
    1/ 1 tests/filesys/base/lg-create
    2/ 2 tests/filesys/base/lg-full
    2/ 2 tests/filesys/base/lg-random
    2/ 2 tests/filesys/base/lg-seq-block
    3/ 3 tests/filesys/base/lg-seq-random
    4/ 4 tests/filesys/base/syn-read
    4/ 4 tests/filesys/base/syn-write
    2/ 2 tests/filesys/base/syn-remove
    ● The source code score break down
    System Call implementation – 35%
    Robustness of system calls – 25%
    Functionality of features which VM might break – 10%
    Functionality of the base system – 30%
    ● This score is scaled down from 100% to 90% to be your “source code score”.
    ● Your “design document” is the remaining 10% of your Project-2 grade.
    ● Check autograder submission score to be consistent with what you get on your VM.
    ● You’ll have unlimited submission, submit early and re-submit.
    Page: 18/19
  9. What to Submit?
  10. You need to write a design document for your project as described in section 6. A soft copy
    of this design document (as text file) should be submitted before the source code deadline.
    The design document is due April 5
    th @11:59 pm.
    (NO LATE SUBMISSION)
  11. You need to submit the complete source tree (all source files) of your project. The whole
    package should compile when the tester simply types make in the source code directory.
    The project source code submission is due April 19
    [email protected]:59 pm.
    (NO LATE SUBMISSION)
    The submission of the design document and the project source code will be done using our
    department’s AutoLab (https://autograder.cse.buffal… system, which will allow you to see
    your grade. The detailed instructions on this will be provided later.
    REFERENCES
    ● Manual adopted from T. Kosar from University at Buffalo
    ● Pintos Reference Manual
    Please add Wx: codehelp