exec函数实现

SYSCALL_DEFINE3(execve,
  const char __user *, filename,
  const char __user *const __user *, argv,
  const char __user *const __user *, envp)
{
 return do_execve(getname(filename), argv, envp);
}
 
 
 
SYSCALL_DEFINE5(execveat,
  int, fd, const char __user *, filename,
  const char __user *const __user *, argv,
  const char __user *const __user *, envp,
  int, flags)
{
 int lookup_flags = (flags & AT_EMPTY_PATH) ? LOOKUP_EMPTY : 0;
 return do_execveat(fd,
      getname_flags(filename, lookup_flags, NULL),
      argv, envp, flags);
}
#ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE3(execve, const char __user *, filename,
 const compat_uptr_t __user *, argv,
 const compat_uptr_t __user *, envp)
{
 return compat_do_execve(getname(filename), argv, envp);
}
COMPAT_SYSCALL_DEFINE5(execveat, int, fd,
         const char __user *, filename,
         const compat_uptr_t __user *, argv,
         const compat_uptr_t __user *, envp,
         int,  flags)
{
 int lookup_flags = (flags & AT_EMPTY_PATH) ? LOOKUP_EMPTY : 0;
 return compat_do_execveat(fd,
      getname_flags(filename, lookup_flags, NULL),
      argv, envp, flags);
}
#endif


/*
 * sys_execve() executes a new program.
 */
static int do_execveat_common(int fd, struct filename *filename,
         struct user_arg_ptr argv,
         struct user_arg_ptr envp,
         int flags)
{
 char *pathbuf = NULL;
 struct linux_binprm *bprm;
 struct file *file;
 struct files_struct *displaced;
 int retval;
 if (IS_ERR(filename))
  return PTR_ERR(filename);
 /*
  * We move the actual failure in case of RLIMIT_NPROC excess from
  * set*uid() to execve() because too many poorly written programs
  * don't check setuid() return code.  Here we additionally recheck
  * whether NPROC limit is still exceeded.
  */
 if ((current->flags & PF_NPROC_EXCEEDED) &&
     atomic_read(¤t_user()->processes) > rlimit(RLIMIT_NPROC)) {
  retval = -EAGAIN;
  goto out_ret;
 }
 /* We're below the limit (still or again), so we don't want to make
  * further execve() calls fail. */
 current->flags &= ~PF_NPROC_EXCEEDED;
 retval = unshare_files(&displaced);
 if (retval)
  goto out_ret;
 retval = -ENOMEM;
 bprm = kzalloc(sizeof(*bprm), GFP_KERNEL);
 if (!bprm)
  goto out_files;
 retval = prepare_bprm_creds(bprm);
 if (retval)
  goto out_free;
 check_unsafe_exec(bprm);
 current->in_execve = 1;
 file = do_open_execat(fd, filename, flags);
 retval = PTR_ERR(file);
 if (IS_ERR(file))
  goto out_unmark;
 sched_exec();
 bprm->file = file;
 if (fd == AT_FDCWD || filename->name[0] == '/') {
  bprm->filename = filename->name;
 } else {
  if (filename->name[0] == '\0')
   pathbuf = kasprintf(GFP_TEMPORARY, "/dev/fd/%d", fd);
  else
   pathbuf = kasprintf(GFP_TEMPORARY, "/dev/fd/%d/%s",
         fd, filename->name);
  if (!pathbuf) {
   retval = -ENOMEM;
   goto out_unmark;
  }
  /*
   * Record that a name derived from an O_CLOEXEC fd will be
   * inaccessible after exec. Relies on having exclusive access to
   * current->files (due to unshare_files above).
   */
  if (close_on_exec(fd, rcu_dereference_raw(current->files->fdt)))
   bprm->interp_flags |= BINPRM_FLAGS_PATH_INACCESSIBLE;
  bprm->filename = pathbuf;
 }
 bprm->interp = bprm->filename;
 retval = bprm_mm_init(bprm);
 if (retval)
  goto out_unmark;
 bprm->argc = count(argv, MAX_ARG_STRINGS);
 if ((retval = bprm->argc) < 0)
  goto out;
 bprm->envc = count(envp, MAX_ARG_STRINGS);
 if ((retval = bprm->envc) < 0)
  goto out;
 retval = prepare_binprm(bprm);
 if (retval < 0)
  goto out;
 retval = copy_strings_kernel(1, &bprm->filename, bprm);
 if (retval < 0)
  goto out;
 bprm->exec = bprm->p;
 retval = copy_strings(bprm->envc, envp, bprm);
 if (retval < 0)
  goto out;
 retval = copy_strings(bprm->argc, argv, bprm);
 if (retval < 0)
  goto out;
 retval = exec_binprm(bprm);
 if (retval < 0)
  goto out;
 /* execve succeeded */
 current->fs->in_exec = 0;
 current->in_execve = 0;
 acct_update_integrals(current);
 task_numa_free(current);
 free_bprm(bprm);
 kfree(pathbuf);
 putname(filename);
 if (displaced)
  put_files_struct(displaced);
 return retval;
out:
 if (bprm->mm) {
  acct_arg_size(bprm, 0);
  mmput(bprm->mm);
 }
out_unmark:
 current->fs->in_exec = 0;
 current->in_execve = 0;
out_free:
 free_bprm(bprm);
 kfree(pathbuf);
out_files:
 if (displaced)
  reset_files_struct(displaced);
out_ret:
 putname(filename);
 return retval;
}