arch/ppc64/boot/crt0.S

   1 /*
   2  * Copyright (C) Paul Mackerras 1997.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License
   6  * as published by the Free Software Foundation; either version
   7  * 2 of the License, or (at your option) any later version.
   8  *
   9  * NOTE: this code runs in 32 bit mode and is packaged as ELF32.
  10  */
  11
  12 #include <asm/ppc_asm.h>
  13
  14         .text
  15         .globl  _start
  16 _start:
  17         lis     r9,_start@h
  18         lis     r8,_etext@ha
  19         addi    r8,r8,_etext@l
  20 1:      dcbf    r0,r9
  21         icbi    r0,r9
  22         addi    r9,r9,0x20
  23         cmplwi  0,r9,8
  24         blt     1b
  25         sync
  26         isync
  27
  28         ## Clear out the BSS as per ANSI C requirements
  29
  30         lis     r7,_end@ha
  31         addi    r7,r7,_end@l            # r7 = &_end
  32         lis     r8,__bss_start@ha       #
  33         addi    r8,r8,__bss_start@l     # r8 = &_bss_start
  34
  35         ## Determine how large an area, in number of words, to clear
  36
  37         subf    r7,r8,r7                # r7 = &_end - &_bss_start + 1
  38         addi    r7,r7,3                 # r7 += 3
  39         srwi.   r7,r7,2                 # r7 = size in words.
  40         beq     3f                      # If the size is zero, don't bother
  41         addi    r8,r8,-4                # r8 -= 4
  42         mtctr   r7                      # SPRN_CTR = number of words to clear
  43         li      r0,0                    # r0 = 0
  44 2:      stwu    r0,4(r8)                # Clear out a word
  45         bdnz    2b                      # Keep clearing until done
  46 3:
  47         b       start
  48