arch/powerpc/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, is position-independent,
  10  * and is packaged as ELF32.
  11  */
  12
  13 #include "ppc_asm.h"
  14
  15         .text
  16         /* A procedure descriptor used when booting this as a COFF file.
  17          * When making COFF, this comes first in the link and we're
  18          * linked at 0x500000.
  19          */
  20         .globl  _zimage_start_opd
  21 _zimage_start_opd:
  22         .long   0x500000, 0, 0, 0
  23
  24 p_start:        .long   _start
  25 p_etext:        .long   _etext
  26 p_bss_start:    .long   __bss_start
  27 p_end:          .long   _end
  28
  29         .weak   _platform_stack_top
  30 p_pstack:       .long   _platform_stack_top
  31
  32         .weak   _zimage_start
  33         .globl  _zimage_start
  34 _zimage_start:
  35         .globl  _zimage_start_lib
  36 _zimage_start_lib:
  37         /* Work out the offset between the address we were linked at
  38            and the address where we're running. */
  39         bl      .+4
  40 p_base: mflr    r10             /* r10 now points to runtime addr of p_base */
  41         /* grab the link address of the dynamic section in r11 */
  42         addis   r11,r10,(_GLOBAL_OFFSET_TABLE_-p_base)@ha
  43         lwz     r11,(_GLOBAL_OFFSET_TABLE_-p_base)@l(r11)
  44         cmpwi   r11,0
  45         beq     3f              /* if not linked -pie */
  46         /* get the runtime address of the dynamic section in r12 */
  47         .weak   __dynamic_start
  48         addis   r12,r10,(__dynamic_start-p_base)@ha
  49         addi    r12,r12,(__dynamic_start-p_base)@l
  50         subf    r11,r11,r12     /* runtime - linktime offset */
  51
  52         /* The dynamic section contains a series of tagged entries.
  53          * We need the RELA and RELACOUNT entries. */
  54 RELA = 7
  55 RELACOUNT = 0x6ffffff9
  56         li      r9,0
  57         li      r0,0
  58 9:      lwz     r8,0(r12)       /* get tag */
  59         cmpwi   r8,0
  60         beq     10f             /* end of list */
  61         cmpwi   r8,RELA
  62         bne     11f
  63         lwz     r9,4(r12)       /* get RELA pointer in r9 */
  64         b       12f
  65 11:     addis   r8,r8,(-RELACOUNT)@ha
  66         cmpwi   r8,RELACOUNT@l
  67         bne     12f
  68         lwz     r0,4(r12)       /* get RELACOUNT value in r0 */
  69 12:     addi    r12,r12,8
  70         b       9b
  71
  72         /* The relocation section contains a list of relocations.
  73          * We now do the R_PPC_RELATIVE ones, which point to words
  74          * which need to be initialized with addend + offset.
  75          * The R_PPC_RELATIVE ones come first and there are RELACOUNT
  76          * of them. */
  77 10:     /* skip relocation if we don't have both */
  78         cmpwi   r0,0
  79         beq     3f
  80         cmpwi   r9,0
  81         beq     3f
  82
  83         add     r9,r9,r11       /* Relocate RELA pointer */
  84         mtctr   r0
  85 2:      lbz     r0,4+3(r9)      /* ELF32_R_INFO(reloc->r_info) */
  86         cmpwi   r0,22           /* R_PPC_RELATIVE */
  87         bne     3f
  88         lwz     r12,0(r9)       /* reloc->r_offset */
  89         lwz     r0,8(r9)        /* reloc->r_addend */
  90         add     r0,r0,r11
  91         stwx    r0,r11,r12
  92         addi    r9,r9,12
  93         bdnz    2b
  94
  95         /* Do a cache flush for our text, in case the loader didn't */
  96 3:      lwz     r9,p_start-p_base(r10)  /* note: these are relocated now */
  97         lwz     r8,p_etext-p_base(r10)
  98 4:      dcbf    r0,r9
  99         icbi    r0,r9
 100         addi    r9,r9,0x20
 101         cmplw   cr0,r9,r8
 102         blt     4b
 103         sync
 104         isync
 105
 106         /* Clear the BSS */
 107         lwz     r9,p_bss_start-p_base(r10)
 108         lwz     r8,p_end-p_base(r10)
 109         li      r0,0
 110 5:      stw     r0,0(r9)
 111         addi    r9,r9,4
 112         cmplw   cr0,r9,r8
 113         blt     5b
 114
 115         /* Possibly set up a custom stack */
 116         lwz     r8,p_pstack-p_base(r10)
 117         cmpwi   r8,0
 118         beq     6f
 119         lwz     r1,0(r8)
 120         li      r0,0
 121         stwu    r0,-16(r1)      /* establish a stack frame */
 122 6:
 123
 124         /* Call platform_init() */
 125         bl      platform_init
 126
 127         /* Call start */
 128         b       start