arch/ppc/boot/common/crt0.S

   1 /*    Copyright (c) 1997 Paul Mackerras <paulus@cs.anu.edu.au>
   2  *      Initial Power Macintosh COFF version.
   3  *    Copyright (c) 1999 Grant Erickson <grant@lcse.umn.edu>
   4  *      Modifications for IBM PowerPC 400-class processor evaluation
   5  *      boards.
   6  *
   7  *    Module name: crt0.S
   8  *
   9  *    Description:
  10  *      Boot loader execution entry point. Clears out .bss section as per
  11  *      ANSI C requirements. Invalidates and flushes the caches over the
  12  *      range covered by the boot loader's .text section. Sets up a stack
  13  *      below the .text section entry point.
  14  *
  15  *    This program is free software; you can redistribute it and/or
  16  *    modify it under the terms of the GNU General Public License
  17  *    as published by the Free Software Foundation; either version
  18  *    2 of the License, or (at your option) any later version.
  19  */
  20
  21 #include <linux/config.h>
  22 #include <asm/ppc_asm.h>
  23
  24         .text
  25
  26         .globl  _start
  27 _start:
  28 #ifdef XCOFF
  29         .long   __start,0,0
  30
  31         .globl  __start
  32 __start:
  33 #endif
  34
  35         ## Flush and invalidate the caches for the range in memory covering
  36         ## the .text section of the boot loader
  37
  38         lis     r9,_start@h             # r9 = &_start
  39         lis     r8,_etext@ha            #
  40         addi    r8,r8,_etext@l          # r8 = &_etext
  41 3:      dcbf    r0,r9                   # Flush the data cache
  42         icbi    r0,r9                   # Invalidate the instruction cache
  43         addi    r9,r9,0x10              # Increment by one cache line
  44         cmplw   cr0,r9,r8               # Are we at the end yet?
  45         blt     3b                      # No, keep flushing and invalidating
  46         sync                            # sync ; isync after flushing the icache
  47         isync
  48
  49         ## Clear out the BSS as per ANSI C requirements
  50
  51         lis     r7,_end@ha
  52         addi    r7,r7,_end@l            # r7 = &_end
  53         lis     r8,__bss_start@ha       #
  54         addi    r8,r8,__bss_start@l     # r8 = &_bss_start
  55
  56         ## Determine how large an area, in number of words, to clear
  57
  58         subf    r7,r8,r7                # r7 = &_end - &_bss_start + 1
  59         addi    r7,r7,3                 # r7 += 3
  60         srwi.   r7,r7,2                 # r7 = size in words.
  61         beq     2f                      # If the size is zero, do not bother
  62         addi    r8,r8,-4                # r8 -= 4
  63         mtctr   r7                      # SPRN_CTR = number of words to clear
  64         li      r0,0                    # r0 = 0
  65 1:      stwu    r0,4(r8)                # Clear out a word
  66         bdnz    1b                      # If we are not done yet, keep clearing
  67 2:
  68
  69 #ifdef CONFIG_40x
  70         ## Set up the stack
  71
  72         lis     r9,_start@h             # r9 = &_start (text section entry)
  73         ori     r9,r9,_start@l
  74         subi    r1,r9,64                # Start the stack 64 bytes below _start
  75         clrrwi  r1,r1,4                 # Make sure it is aligned on 16 bytes.
  76         li      r0,0
  77         stwu    r0,-16(r1)
  78         mtlr    r9
  79 #endif
  80
  81         b       start                   # All done, start the real work.