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#include "userprog/process.h"
#include <debug.h>
#include <inttypes.h>
#include <round.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "userprog/gdt.h"
#include "userprog/pagedir.h"
#include "userprog/tss.h"
#include "filesys/directory.h"
#include "filesys/file.h"
#include "filesys/filesys.h"
#include "threads/flags.h"
#include "threads/init.h"
#include "threads/interrupt.h"
#include "threads/malloc.h"
#include "threads/palloc.h"
#include "threads/thread.h"
#include "threads/vaddr.h"
static thread_func start_process NO_RETURN;
static bool load (const char *cmd_line, void (**eip) (void), void **esp);
/* Data structure shared between process_execute() in the
invoking thread and start_process() in the newly invoked
thread. */
struct exec_info
const char *file_name; /* Program to load. */
struct semaphore load_done; /* "Up"ed when loading complete. */
struct wait_status *wait_status; /* Child process. */
bool success; /* Program successfully loaded? */
/* Starts a new thread running a user program loaded from
FILENAME. The new thread may be scheduled (and may even exit)
before process_execute() returns. Returns the new process's
thread id, or TID_ERROR if the thread cannot be created. */
process_execute (const char *file_name)
struct exec_info exec;
char thread_name[16];
char *save_ptr;
tid_t tid;
/* Initialize exec_info. */
exec.file_name = file_name;
sema_init (&exec.load_done, 0);
/* Create a new thread to execute FILE_NAME. */
strlcpy (thread_name, file_name, sizeof thread_name);
strtok_r (thread_name, " ", &save_ptr);
tid = thread_create (thread_name, PRI_DEFAULT, start_process, &exec);
if (tid != TID_ERROR)
sema_down (&exec.load_done);
if (exec.success)
list_push_back (&thread_current ()->children, &exec.wait_status->elem);
tid = TID_ERROR;
return tid;
/* A thread function that loads a user process and starts it
running. */
static void
start_process (void *exec_)
struct exec_info *exec = exec_;
struct intr_frame if_;
bool success;
/* Initialize interrupt frame and load executable. */
memset (&if_, 0, sizeof if_); = if_.fs = = if_.ds = = SEL_UDSEG;
if_.cs = SEL_UCSEG;
if_.eflags = FLAG_IF | FLAG_MBS;
success = load (exec->file_name, &if_.eip, &if_.esp);
/* Allocate wait_status. */
if (success)
exec->wait_status = thread_current ()->wait_status
= malloc (sizeof *exec->wait_status);
success = exec->wait_status != NULL;
/* Initialize wait_status. */
if (success)
lock_init (&exec->wait_status->lock);
exec->wait_status->ref_cnt = 2;
exec->wait_status->tid = thread_current ()->tid;
exec->wait_status->exit_code = -1;
sema_init (&exec->wait_status->dead, 0);
/* Notify parent thread and clean up. */
exec->success = success;
sema_up (&exec->load_done);
if (!success)
thread_exit ();
/* Start the user process by simulating a return from an
interrupt, implemented by intr_exit (in
threads/intr-stubs.S). Because intr_exit takes all of its
arguments on the stack in the form of a `struct intr_frame',
we just point the stack pointer (%esp) to our stack frame
and jump to it. */
asm volatile ("movl %0, %%esp; jmp intr_exit" : : "g" (&if_) : "memory");
/* Releases one reference to CS and, if it is now unreferenced,
frees it. */
static void
release_child (struct wait_status *cs)
int new_ref_cnt;
lock_acquire (&cs->lock);
new_ref_cnt = --cs->ref_cnt;
lock_release (&cs->lock);
if (new_ref_cnt == 0)
free (cs);
/* Waits for thread TID to die and returns its exit status. If
it was terminated by the kernel (i.e. killed due to an
exception), returns -1. If TID is invalid or if it was not a
child of the calling process, or if process_wait() has already
been successfully called for the given TID, returns -1
immediately, without waiting. */
process_wait (tid_t child_tid)
struct list_elem * e;
struct wait_status * t = NULL;
struct thread * cur = thread_current();
for (e = list_begin (&cur->children); e != list_end (&cur->children);e = list_next (e)){
struct wait_status * t2 = list_entry (e, struct wait_status, elem);
if (t2->tid == child_tid){t = t2; break;}
if (t == NULL){return -1;}
//int temp = t->exit_code;
//t->exit_code = -1;
return t->exit_code;
/* Free the current process's resources. */
process_exit (void)
struct thread *cur = thread_current ();
struct list_elem *e, *next;
uint32_t *pd;
/* Close executable (and allow writes). */
file_close (cur->bin_file);
/* Notify parent that we're dead. */
if (cur->wait_status != NULL)
struct wait_status *cs = cur->wait_status;
/* add code */
printf ("%s: exit(0)\n", cur->name); // HACK all successful ;-)
release_child (cs);
/* Free entries of children list. */
for (e = list_begin (&cur->children); e != list_end (&cur->children);
e = next)
struct wait_status *cs = list_entry (e, struct wait_status, elem);
next = list_remove (e);
release_child (cs);
/* Destroy the current process's page directory and switch back
to the kernel-only page directory. */
pd = cur->pagedir;
if (pd != NULL)
/* Correct ordering here is crucial. We must set
cur->pagedir to NULL before switching page directories,
so that a timer interrupt can't switch back to the
process page directory. We must activate the base page
directory before destroying the process's page
directory, or our active page directory will be one
that's been freed (and cleared). */
cur->pagedir = NULL;
pagedir_activate (NULL);
pagedir_destroy (pd);
/* Sets up the CPU for running user code in the current
This function is called on every context switch. */
process_activate (void)
struct thread *t = thread_current ();
/* Activate thread's page tables. */
pagedir_activate (t->pagedir);
/* Set thread's kernel stack for use in processing
interrupts. */
tss_update ();
/* We load ELF binaries. The following definitions are taken
from the ELF specification, [ELF1], more-or-less verbatim. */
/* ELF types. See [ELF1] 1-2. */
typedef uint32_t Elf32_Word, Elf32_Addr, Elf32_Off;
typedef uint16_t Elf32_Half;
/* For use with ELF types in printf(). */
#define PE32Wx PRIx32 /* Print Elf32_Word in hexadecimal. */
#define PE32Ax PRIx32 /* Print Elf32_Addr in hexadecimal. */
#define PE32Ox PRIx32 /* Print Elf32_Off in hexadecimal. */
#define PE32Hx PRIx16 /* Print Elf32_Half in hexadecimal. */
/* Executable header. See [ELF1] 1-4 to 1-8.
This appears at the very beginning of an ELF binary. */
struct Elf32_Ehdr
unsigned char e_ident[16];
Elf32_Half e_type;
Elf32_Half e_machine;
Elf32_Word e_version;
Elf32_Addr e_entry;
Elf32_Off e_phoff;
Elf32_Off e_shoff;
Elf32_Word e_flags;
Elf32_Half e_ehsize;
Elf32_Half e_phentsize;
Elf32_Half e_phnum;
Elf32_Half e_shentsize;
Elf32_Half e_shnum;
Elf32_Half e_shstrndx;
/* Program header. See [ELF1] 2-2 to 2-4.
There are e_phnum of these, starting at file offset e_phoff
(see [ELF1] 1-6). */
struct Elf32_Phdr
Elf32_Word p_type;
Elf32_Off p_offset;
Elf32_Addr p_vaddr;
Elf32_Addr p_paddr;
Elf32_Word p_filesz;
Elf32_Word p_memsz;
Elf32_Word p_flags;
Elf32_Word p_align;
/* Values for p_type. See [ELF1] 2-3. */
#define PT_NULL 0 /* Ignore. */
#define PT_LOAD 1 /* Loadable segment. */
#define PT_DYNAMIC 2 /* Dynamic linking info. */
#define PT_INTERP 3 /* Name of dynamic loader. */
#define PT_NOTE 4 /* Auxiliary info. */
#define PT_SHLIB 5 /* Reserved. */
#define PT_PHDR 6 /* Program header table. */
#define PT_STACK 0x6474e551 /* Stack segment. */
/* Flags for p_flags. See [ELF3] 2-3 and 2-4. */
#define PF_X 1 /* Executable. */
#define PF_W 2 /* Writable. */
#define PF_R 4 /* Readable. */
static bool setup_stack (const char *cmd_line, void **esp);
static bool validate_segment (const struct Elf32_Phdr *, struct file *);
static bool load_segment (struct file *file, off_t ofs, uint8_t *upage,
uint32_t read_bytes, uint32_t zero_bytes,
bool writable);
/* Loads an ELF executable from FILE_NAME into the current thread.
Stores the executable's entry point into *EIP
and its initial stack pointer into *ESP.
Returns true if successful, false otherwise. */
load (const char *cmd_line, void (**eip) (void), void **esp)
struct thread *t = thread_current ();
char file_name[NAME_MAX + 2];
struct Elf32_Ehdr ehdr;
struct file *file = NULL;
off_t file_ofs;
bool success = false;
char *cp;
int i;
/* Allocate and activate page directory. */
t->pagedir = pagedir_create ();
if (t->pagedir == NULL)
goto done;
process_activate ();
/* Extract file_name from command line. */
while (*cmd_line == ' ')
strlcpy (file_name, cmd_line, sizeof file_name);
cp = strchr (file_name, ' ');
if (cp != NULL)
*cp = '\0';
/* Open executable file. */
t->bin_file = file = filesys_open (file_name);
if (file == NULL)
printf ("load: %s: open failed\n", file_name);
goto done;
file_deny_write (file);
/* Read and verify executable header. */
if (file_read (file, &ehdr, sizeof ehdr) != sizeof ehdr
|| memcmp (ehdr.e_ident, "\177ELF\1\1\1", 7)
|| ehdr.e_type != 2
|| ehdr.e_machine != 3
|| ehdr.e_version != 1
|| ehdr.e_phentsize != sizeof (struct Elf32_Phdr)
|| ehdr.e_phnum > 1024)
printf ("load: %s: error loading executable\n", file_name);
goto done;
/* Read program headers. */
file_ofs = ehdr.e_phoff;
for (i = 0; i < ehdr.e_phnum; i++)
struct Elf32_Phdr phdr;
if (file_ofs < 0 || file_ofs > file_length (file))
goto done;
file_seek (file, file_ofs);
if (file_read (file, &phdr, sizeof phdr) != sizeof phdr)
goto done;
file_ofs += sizeof phdr;
switch (phdr.p_type)
case PT_NULL:
case PT_NOTE:
case PT_PHDR:
case PT_STACK:
/* Ignore this segment. */
case PT_SHLIB:
goto done;
case PT_LOAD:
if (validate_segment (&phdr, file))
bool writable = (phdr.p_flags & PF_W) != 0;
uint32_t file_page = phdr.p_offset & ~PGMASK;
uint32_t mem_page = phdr.p_vaddr & ~PGMASK;
uint32_t page_offset = phdr.p_vaddr & PGMASK;
uint32_t read_bytes, zero_bytes;
if (phdr.p_filesz > 0)
/* Normal segment.
Read initial part from disk and zero the rest. */
read_bytes = page_offset + phdr.p_filesz;
zero_bytes = (ROUND_UP (page_offset + phdr.p_memsz, PGSIZE)
- read_bytes);
/* Entirely zero.
Don't read anything from disk. */
read_bytes = 0;
zero_bytes = ROUND_UP (page_offset + phdr.p_memsz, PGSIZE);
if (!load_segment (file, file_page, (void *) mem_page,
read_bytes, zero_bytes, writable))
goto done;
goto done;
/* Set up stack. */
if (!setup_stack (cmd_line, esp))
goto done;
/* Start address. */
*eip = (void (*) (void)) ehdr.e_entry;
success = true;
/* We arrive here whether the load is successful or not. */
return success;
/* load() helpers. */
static bool install_page (void *upage, void *kpage, bool writable);
/* Checks whether PHDR describes a valid, loadable segment in
FILE and returns true if so, false otherwise. */
static bool
validate_segment (const struct Elf32_Phdr *phdr, struct file *file)
/* p_offset and p_vaddr must have the same page offset. */
if ((phdr->p_offset & PGMASK) != (phdr->p_vaddr & PGMASK))
return false;
/* p_offset must point within FILE. */
if (phdr->p_offset > (Elf32_Off) file_length (file))
return false;
/* p_memsz must be at least as big as p_filesz. */
if (phdr->p_memsz < phdr->p_filesz)
return false;
/* The segment must not be empty. */
if (phdr->p_memsz == 0)
return false;
/* The virtual memory region must both start and end within the
user address space range. */
if (!is_user_vaddr ((void *) phdr->p_vaddr))
return false;
if (!is_user_vaddr ((void *) (phdr->p_vaddr + phdr->p_memsz)))
return false;
/* The region cannot "wrap around" across the kernel virtual
address space. */
if (phdr->p_vaddr + phdr->p_memsz < phdr->p_vaddr)
return false;
/* Disallow mapping page 0.
Not only is it a bad idea to map page 0, but if we allowed
it then user code that passed a null pointer to system calls
could quite likely panic the kernel by way of null pointer
assertions in memcpy(), etc. */
if (phdr->p_vaddr < PGSIZE)
return false;
/* It's okay. */
return true;
/* Loads a segment starting at offset OFS in FILE at address
UPAGE. In total, READ_BYTES + ZERO_BYTES bytes of virtual
memory are initialized, as follows:
- READ_BYTES bytes at UPAGE must be read from FILE
starting at offset OFS.
- ZERO_BYTES bytes at UPAGE + READ_BYTES must be zeroed.
The pages initialized by this function must be writable by the
user process if WRITABLE is true, read-only otherwise.
Return true if successful, false if a memory allocation error
or disk read error occurs. */
static bool
load_segment (struct file *file, off_t ofs, uint8_t *upage,
uint32_t read_bytes, uint32_t zero_bytes, bool writable)
ASSERT ((read_bytes + zero_bytes) % PGSIZE == 0);
ASSERT (pg_ofs (upage) == 0);
ASSERT (ofs % PGSIZE == 0);
file_seek (file, ofs);
while (read_bytes > 0 || zero_bytes > 0)
/* Calculate how to fill this page.
We will read PAGE_READ_BYTES bytes from FILE
and zero the final PAGE_ZERO_BYTES bytes. */
size_t page_read_bytes = read_bytes < PGSIZE ? read_bytes : PGSIZE;
size_t page_zero_bytes = PGSIZE - page_read_bytes;
/* Get a page of memory. */
uint8_t *kpage = palloc_get_page (PAL_USER);
if (kpage == NULL)
return false;
/* Load this page. */
if (file_read (file, kpage, page_read_bytes) != (int) page_read_bytes)
palloc_free_page (kpage);
return false;
memset (kpage + page_read_bytes, 0, page_zero_bytes);
/* Add the page to the process's address space. */
if (!install_page (upage, kpage, writable))
palloc_free_page (kpage);
return false;
/* Advance. */
read_bytes -= page_read_bytes;
zero_bytes -= page_zero_bytes;
upage += PGSIZE;
return true;
/* Reverse the order of the ARGC pointers to char in ARGV. */
static void
reverse (int argc, char **argv)
/* add code */
/* Pushes the SIZE bytes in BUF onto the stack in KPAGE, whose
page-relative stack pointer is *OFS, and then adjusts *OFS
appropriately. The bytes pushed are rounded to a 32-bit
If successful, returns a pointer to the newly pushed object.
On failure, returns a null pointer. */
static void *
push (uint8_t *kpage, size_t *ofs, const void *buf, size_t size)
size_t padsize = ROUND_UP (size, sizeof (uint32_t));
if (*ofs < padsize)
return NULL;
*ofs -= padsize;
memcpy (kpage + *ofs + (padsize - size), buf, size);
return kpage + *ofs + (padsize - size);
/* Sets up command line arguments in KPAGE, which will be mapped
to UPAGE in user space. The command line arguments are taken
from CMD_LINE, separated by spaces. Sets *ESP to the initial
stack pointer for the process. */
static bool
init_cmd_line (uint8_t *kpage, uint8_t *upage, const char *cmd_line,
void **esp)
size_t ofs = PGSIZE;
char *const null = NULL;
char *cmd_line_copy;
char *karg, *saveptr;
int argc;
char **argv;
/* Push a temporary working copy of the command line string. */
cmd_line_copy = push (kpage, &ofs, cmd_line, strlen (cmd_line) + 1);
if (cmd_line_copy == NULL)
return false;
if (push (kpage, &ofs, &null, sizeof null) == NULL)
return false;
/* Parse the working copy of the command line into arguments
and push them in reverse order. */
argc = 0;
for (karg = strtok_r (cmd_line_copy, " ", &saveptr); karg != NULL;
karg = strtok_r (NULL, " ", &saveptr))
void *uarg = upage + (karg - (char *) kpage);
if (push (kpage, &ofs, &uarg, sizeof uarg) == NULL)
return false;
/* Reverse the order of the command line arguments. */
argv = (char **) (upage + ofs);
reverse (argc, (char **) (kpage + ofs));
/* Push argv, argc, "return address". */
if (push (kpage, &ofs, &argv, sizeof argv) == NULL
|| push (kpage, &ofs, &argc, sizeof argc) == NULL
|| push (kpage, &ofs, &null, sizeof null) == NULL)
return false;
/* Set initial stack pointer. */
*esp = upage + ofs;
return true;
/* Create a minimal stack by mapping a page at the
top of user virtual memory. Fill in the page using CMD_LINE
and sets *ESP to the stack pointer. */
static bool
setup_stack (const char *cmd_line, void **esp)
uint8_t *kpage;
bool success = false;
kpage = palloc_get_page (PAL_USER | PAL_ZERO);
if (kpage != NULL)
uint8_t *upage = ((uint8_t *) PHYS_BASE) - PGSIZE;
success = install_page (upage, kpage, true);
if (success)
success = init_cmd_line (kpage, upage, cmd_line, esp);
palloc_free_page (kpage);
return success;
/* Adds a mapping from user virtual address UPAGE to kernel
virtual address KPAGE to the page table.
If WRITABLE is true, the user process may modify the page;
otherwise, it is read-only.
UPAGE must not already be mapped.
KPAGE should probably be a page obtained from the user pool
with palloc_get_page().
Returns true on success, false if UPAGE is already mapped or
if memory allocation fails. */
static bool
install_page (void *upage, void *kpage, bool writable)
struct thread *t = thread_current ();
/* Verify that there's not already a page at that virtual
address, then map our page there. */
return (pagedir_get_page (t->pagedir, upage) == NULL
&& pagedir_set_page (t->pagedir, upage, kpage, writable));
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