exec.c

Minix3.11的源码。[MINIX 3是一个为高可靠性应用而设计的自由且简洁的类UNIX系统。]

/* Allocate new memory and release the old memory.  Change the map and report
 * the new map to the kernel.  Zero the new core image's bss, gap and stack.
 */

  register struct mproc *rmp = mp;
  vir_clicks text_clicks, data_clicks, gap_clicks, stack_clicks, tot_clicks;
  phys_clicks new_base;
  phys_bytes bytes, base, bss_offset;
  int s;

  /* No need to allocate text if it can be shared. */
  if (sh_mp != NULL) text_bytes = 0;

  /* Allow the old data to be swapped out to make room.  (Which is really a
   * waste of time, because we are going to throw it away anyway.)
   */
  rmp->mp_flags |= WAITING;

  /* Acquire the new memory.  Each of the 4 parts: text, (data+bss), gap,
   * and stack occupies an integral number of clicks, starting at click
   * boundary.  The data and bss parts are run together with no space.
   */
  text_clicks = ((unsigned long) text_bytes + CLICK_SIZE - 1) >> CLICK_SHIFT;
  data_clicks = (data_bytes + bss_bytes + CLICK_SIZE - 1) >> CLICK_SHIFT;
  stack_clicks = (stk_bytes + CLICK_SIZE - 1) >> CLICK_SHIFT;
  tot_clicks = (tot_bytes + CLICK_SIZE - 1) >> CLICK_SHIFT;
  gap_clicks = tot_clicks - data_clicks - stack_clicks;
  if ( (int) gap_clicks < 0) return(ENOMEM);

  /* Try to allocate memory for the new process. */
  new_base = alloc_mem(text_clicks + tot_clicks);
  if (new_base == NO_MEM) return(ENOMEM);

  /* We've got memory for the new core image.  Release the old one. */
  rmp = mp;

  if (find_share(rmp, rmp->mp_ino, rmp->mp_dev, rmp->mp_ctime) == NULL) {
	/* No other process shares the text segment, so free it. */
	free_mem(rmp->mp_seg[T].mem_phys, rmp->mp_seg[T].mem_len);
  }
  /* Free the data and stack segments. */
  free_mem(rmp->mp_seg[D].mem_phys,
   rmp->mp_seg[S].mem_vir + rmp->mp_seg[S].mem_len - rmp->mp_seg[D].mem_vir);

  /* We have now passed the point of no return.  The old core image has been
   * forever lost, memory for a new core image has been allocated.  Set up
   * and report new map.
   */
  if (sh_mp != NULL) {
	/* Share the text segment. */
	rmp->mp_seg[T] = sh_mp->mp_seg[T];
  } else {
	rmp->mp_seg[T].mem_phys = new_base;
	rmp->mp_seg[T].mem_vir = 0;
	rmp->mp_seg[T].mem_len = text_clicks;
  }
  rmp->mp_seg[D].mem_phys = new_base + text_clicks;
  rmp->mp_seg[D].mem_vir = 0;
  rmp->mp_seg[D].mem_len = data_clicks;
  rmp->mp_seg[S].mem_phys = rmp->mp_seg[D].mem_phys + data_clicks + gap_clicks;
  rmp->mp_seg[S].mem_vir = rmp->mp_seg[D].mem_vir + data_clicks + gap_clicks;
  rmp->mp_seg[S].mem_len = stack_clicks;

#if (CHIP == M68000)
  rmp->mp_seg[T].mem_vir = 0;
  rmp->mp_seg[D].mem_vir = rmp->mp_seg[T].mem_len;
  rmp->mp_seg[S].mem_vir = rmp->mp_seg[D].mem_vir 
  	+ rmp->mp_seg[D].mem_len + gap_clicks;
#endif

  sys_newmap(who, rmp->mp_seg);   /* report new map to the kernel */

  /* The old memory may have been swapped out, but the new memory is real. */
  rmp->mp_flags &= ~(WAITING|ONSWAP|SWAPIN);

  /* Zero the bss, gap, and stack segment. */
  bytes = (phys_bytes)(data_clicks + gap_clicks + stack_clicks) << CLICK_SHIFT;
  base = (phys_bytes) rmp->mp_seg[D].mem_phys << CLICK_SHIFT;
  bss_offset = (data_bytes >> CLICK_SHIFT) << CLICK_SHIFT;
  base += bss_offset;
  bytes -= bss_offset;

  if ((s=sys_memset(0, base, bytes)) != OK) {
	panic(__FILE__,"new_mem can't zero", s);
  }

  return(OK);
}

/*===========================================================================*
 *				patch_ptr				     *
 *===========================================================================*/
PRIVATE void patch_ptr(stack, base)
char stack[ARG_MAX];		/* pointer to stack image within PM */
vir_bytes base;			/* virtual address of stack base inside user */
{
/* When doing an exec(name, argv, envp) call, the user builds up a stack
 * image with arg and env pointers relative to the start of the stack.  Now
 * these pointers must be relocated, since the stack is not positioned at
 * address 0 in the user's address space.
 */

  char **ap, flag;
  vir_bytes v;

  flag = 0;			/* counts number of 0-pointers seen */
  ap = (char **) stack;		/* points initially to 'nargs' */
  ap++;				/* now points to argv[0] */
  while (flag < 2) {
	if (ap >= (char **) &stack[ARG_MAX]) return;	/* too bad */
	if (*ap != NULL) {
		v = (vir_bytes) *ap;	/* v is relative pointer */
		v += base;		/* relocate it */
		*ap = (char *) v;	/* put it back */
	} else {
		flag++;
	}
	ap++;
  }
}

/*===========================================================================*
 *				insert_arg				     *
 *===========================================================================*/
PRIVATE int insert_arg(stack, stk_bytes, arg, replace)
char stack[ARG_MAX];		/* pointer to stack image within PM */
vir_bytes *stk_bytes;		/* size of initial stack */
char *arg;			/* argument to prepend/replace as new argv[0] */
int replace;
{
/* Patch the stack so that arg will become argv[0].  Be careful, the stack may
 * be filled with garbage, although it normally looks like this:
 *	nargs argv[0] ... argv[nargs-1] NULL envp[0] ... NULL
 * followed by the strings "pointed" to by the argv[i] and the envp[i].  The
 * pointers are really offsets from the start of stack.
 * Return true iff the operation succeeded.
 */
  int offset, a0, a1, old_bytes = *stk_bytes;

  /* Prepending arg adds at least one string and a zero byte. */
  offset = strlen(arg) + 1;

  a0 = (int) ((char **) stack)[1];	/* argv[0] */
  if (a0 < 4 * PTRSIZE || a0 >= old_bytes) return(FALSE);

  a1 = a0;			/* a1 will point to the strings to be moved */
  if (replace) {
	/* Move a1 to the end of argv[0][] (argv[1] if nargs > 1). */
	do {
		if (a1 == old_bytes) return(FALSE);
		--offset;
	} while (stack[a1++] != 0);
  } else {
	offset += PTRSIZE;	/* new argv[0] needs new pointer in argv[] */
	a0 += PTRSIZE;		/* location of new argv[0][]. */
  }

  /* stack will grow by offset bytes (or shrink by -offset bytes) */
  if ((*stk_bytes += offset) > ARG_MAX) return(FALSE);

  /* Reposition the strings by offset bytes */
  memmove(stack + a1 + offset, stack + a1, old_bytes - a1);

  strcpy(stack + a0, arg);	/* Put arg in the new space. */

  if (!replace) {
	/* Make space for a new argv[0]. */
	memmove(stack + 2 * PTRSIZE, stack + 1 * PTRSIZE, a0 - 2 * PTRSIZE);

	((char **) stack)[0]++;	/* nargs++; */
  }
  /* Now patch up argv[] and envp[] by offset. */
  patch_ptr(stack, (vir_bytes) offset);
  ((char **) stack)[1] = (char *) a0;	/* set argv[0] correctly */
  return(TRUE);
}

/*===========================================================================*
 *				patch_stack				     *
 *===========================================================================*/
PRIVATE char *patch_stack(fd, stack, stk_bytes, script)
int fd;				/* file descriptor to open script file */
char stack[ARG_MAX];		/* pointer to stack image within PM */
vir_bytes *stk_bytes;		/* size of initial stack */
char *script;			/* name of script to interpret */
{
/* Patch the argument vector to include the path name of the script to be
 * interpreted, and all strings on the #! line.  Returns the path name of
 * the interpreter.
 */
  char *sp, *interp = NULL;
  int n;
  enum { INSERT=FALSE, REPLACE=TRUE };

  /* Make script[] the new argv[0]. */
  if (!insert_arg(stack, stk_bytes, script, REPLACE)) return(NULL);

  if (lseek(fd, 2L, 0) == -1			/* just behind the #! */
    || (n= read(fd, script, PATH_MAX)) < 0	/* read line one */
    || (sp= memchr(script, '\n', n)) == NULL)	/* must be a proper line */
	return(NULL);

  /* Move sp backwards through script[], prepending each string to stack. */
  for (;;) {
	/* skip spaces behind argument. */
	while (sp > script && (*--sp == ' ' || *sp == '\t')) {}
	if (sp == script) break;

	sp[1] = 0;
	/* Move to the start of the argument. */
	while (sp > script && sp[-1] != ' ' && sp[-1] != '\t') --sp;

	interp = sp;
	if (!insert_arg(stack, stk_bytes, sp, INSERT)) return(NULL);
  }

  /* Round *stk_bytes up to the size of a pointer for alignment contraints. */
  *stk_bytes= ((*stk_bytes + PTRSIZE - 1) / PTRSIZE) * PTRSIZE;

  close(fd);
  return(interp);
}

/*===========================================================================*
 *				rw_seg					     *
 *===========================================================================*/
PUBLIC void rw_seg(rw, fd, proc, seg, seg_bytes0)
int rw;				/* 0 = read, 1 = write */
int fd;				/* file descriptor to read from / write to */
int proc;			/* process number */
int seg;			/* T, D, or S */
phys_bytes seg_bytes0;		/* how much is to be transferred? */
{
/* Transfer text or data from/to a file and copy to/from a process segment.
 * This procedure is a little bit tricky.  The logical way to transfer a
 * segment would be block by block and copying each block to/from the user
 * space one at a time.  This is too slow, so we do something dirty here,
 * namely send the user space and virtual address to the file system in the
 * upper 10 bits of the file descriptor, and pass it the user virtual address
 * instead of a PM address.  The file system extracts these parameters when 
 * gets a read or write call from the process manager, which is the only 
 * process that is permitted to use this trick.  The file system then copies 
 * the whole segment directly to/from user space, bypassing PM completely.
 *
 * The byte count on read is usually smaller than the segment count, because
 * a segment is padded out to a click multiple, and the data segment is only
 * partially initialized.
 */

  int new_fd, bytes, r;
  char *ubuf_ptr;
  struct mem_map *sp = &mproc[proc].mp_seg[seg];
  phys_bytes seg_bytes = seg_bytes0;

  new_fd = (proc << 7) | (seg << 5) | fd;
  ubuf_ptr = (char *) ((vir_bytes) sp->mem_vir << CLICK_SHIFT);

  while (seg_bytes != 0) {
#define PM_CHUNK_SIZE 8192
	bytes = MIN((INT_MAX / PM_CHUNK_SIZE) * PM_CHUNK_SIZE, seg_bytes);
	if (rw == 0) {
		r = read(new_fd, ubuf_ptr, bytes);
	} else {
		r = write(new_fd, ubuf_ptr, bytes);
	}
	if (r != bytes) break;
	ubuf_ptr += bytes;
	seg_bytes -= bytes;
  }
}

/*===========================================================================*
 *				find_share				     *
 *===========================================================================*/
PUBLIC struct mproc *find_share(mp_ign, ino, dev, ctime)
struct mproc *mp_ign;		/* process that should not be looked at */
ino_t ino;			/* parameters that uniquely identify a file */
dev_t dev;
time_t ctime;
{
/* Look for a process that is the file <ino, dev, ctime> in execution.  Don't
 * accidentally "find" mp_ign, because it is the process on whose behalf this
 * call is made.
 */
  struct mproc *sh_mp;
  for (sh_mp = &mproc[0]; sh_mp < &mproc[NR_PROCS]; sh_mp++) {

	if (!(sh_mp->mp_flags & SEPARATE)) continue;
	if (sh_mp == mp_ign) continue;
	if (sh_mp->mp_ino != ino) continue;
	if (sh_mp->mp_dev != dev) continue;
	if (sh_mp->mp_ctime != ctime) continue;
	return sh_mp;
  }
  return(NULL);
}