usr/src/cmd/sgs/rtld.4.x/zero.s

   1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License, Version 1.0 only
   6  * (the "License").  You may not use this file except in compliance
   7  * with the License.
   8  *
   9  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
  10  * or http://www.opensolaris.org/os/licensing.
  11  * See the License for the specific language governing permissions
  12  * and limitations under the License.
  13  *
  14  * When distributing Covered Code, include this CDDL HEADER in each
  15  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  16  * If applicable, add the following below this CDDL HEADER, with the
  17  * fields enclosed by brackets "[]" replaced with your own identifying
  18  * information: Portions Copyright [yyyy] [name of copyright owner]
  19  *
  20  * CDDL HEADER END
  21  */
  22 /*
  23  *      Copyright (c) 1990, 1991 Sun Microsystems, Inc.
  24  */
  25
  26 #ident  "%Z%%M% %I%     %E% SMI"
  27
  28 /*
  29  * Routine to zero out a section of memory (the tail end of the data segment
  30  * upto a page boundary).  First nibble off any bytes up to the first double
  31  * aligned word, and then clear doubles until the byte count is zero.  Note,
  32  * this assumes the count specified has been rounded to end on a double word
  33  * boundary.
  34  *
  35  *      %o0 = addr, %o1 = len
  36  */
  37
  38         .seg    "text"
  39         .global __zero
  40 __zero:
  41         tst     %o1             ! Have we any count at all?
  42         ba      3f              ! Go find out,
  43         clr     %g1             !   but prepare for long loop
  44
  45 ! Byte clearing loop
  46
  47 0:
  48         inc     %o0             ! Bump address
  49         deccc   %o1             ! Decrement count
  50 3:
  51         bz      1f              ! If no count left, exit
  52         andcc   %o0, 7, %g0     ! Is the address less than double-word aligned?
  53         bnz,a   0b              ! Branch if so
  54         clrb    [%o0]           !   but clear the current byte anyway
  55
  56 ! Double clearing loop
  57
  58 2:
  59         std     %g0, [%o0]      ! Clear next 8 bytes
  60         subcc   %o1, 8, %o1     ! Decrement count
  61         bnz     2b              ! Branch if any left
  62         inc     8, %o0          !   but always increment address by 8
  63 1:
  64         retl                    ! Go home
  65         nop