arch/i386/boot/compressed/head.S

   1 /*
   2  *  linux/boot/head.S
   3  *
   4  *  Copyright (C) 1991, 1992, 1993  Linus Torvalds
   5  */
   6
   7 /*
   8  *  head.S contains the 32-bit startup code.
   9  *
  10  * NOTE!!! Startup happens at absolute address 0x00001000, which is also where
  11  * the page directory will exist. The startup code will be overwritten by
  12  * the page directory. [According to comments etc elsewhere on a compressed
  13  * kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC]
  14  *
  15  * Page 0 is deliberately kept safe, since System Management Mode code in
  16  * laptops may need to access the BIOS data stored there.  This is also
  17  * useful for future device drivers that either access the BIOS via VM86
  18  * mode.
  19  */
  20
  21 /*
  22  * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
  23  */
  24 .text
  25
  26 #include <linux/linkage.h>
  27 #include <asm/segment.h>
  28 #include <asm/page.h>
  29 #include <asm/boot.h>
  30
  31 .section ".text.head"
  32         .globl startup_32
  33
  34 startup_32:
  35         cld
  36         cli
  37         movl $(__BOOT_DS),%eax
  38         movl %eax,%ds
  39         movl %eax,%es
  40         movl %eax,%fs
  41         movl %eax,%gs
  42         movl %eax,%ss
  43
  44 /* Calculate the delta between where we were compiled to run
  45  * at and where we were actually loaded at.  This can only be done
  46  * with a short local call on x86.  Nothing  else will tell us what
  47  * address we are running at.  The reserved chunk of the real-mode
  48  * data at 0x34-0x3f are used as the stack for this calculation.
  49  * Only 4 bytes are needed.
  50  */
  51         leal 0x40(%esi), %esp
  52         call 1f
  53 1:      popl %ebp
  54         subl $1b, %ebp
  55
  56 /* %ebp contains the address we are loaded at by the boot loader and %ebx
  57  * contains the address where we should move the kernel image temporarily
  58  * for safe in-place decompression.
  59  */
  60
  61 #ifdef CONFIG_RELOCATABLE
  62         movl    %ebp, %ebx
  63         addl    $(CONFIG_PHYSICAL_ALIGN - 1), %ebx
  64         andl    $(~(CONFIG_PHYSICAL_ALIGN - 1)), %ebx
  65 #else
  66         movl $LOAD_PHYSICAL_ADDR, %ebx
  67 #endif
  68
  69         /* Replace the compressed data size with the uncompressed size */
  70         subl input_len(%ebp), %ebx
  71         movl output_len(%ebp), %eax
  72         addl %eax, %ebx
  73         /* Add 8 bytes for every 32K input block */
  74         shrl $12, %eax
  75         addl %eax, %ebx
  76         /* Add 32K + 18 bytes of extra slack */
  77         addl $(32768 + 18), %ebx
  78         /* Align on a 4K boundary */
  79         addl $4095, %ebx
  80         andl $~4095, %ebx
  81
  82 /* Copy the compressed kernel to the end of our buffer
  83  * where decompression in place becomes safe.
  84  */
  85         pushl %esi
  86         leal _end(%ebp), %esi
  87         leal _end(%ebx), %edi
  88         movl $(_end - startup_32), %ecx
  89         std
  90         rep
  91         movsb
  92         cld
  93         popl %esi
  94
  95 /* Compute the kernel start address.
  96  */
  97 #ifdef CONFIG_RELOCATABLE
  98         addl    $(CONFIG_PHYSICAL_ALIGN - 1), %ebp
  99         andl    $(~(CONFIG_PHYSICAL_ALIGN - 1)), %ebp
 100 #else
 101         movl    $LOAD_PHYSICAL_ADDR, %ebp
 102 #endif
 103
 104 /*
 105  * Jump to the relocated address.
 106  */
 107         leal relocated(%ebx), %eax
 108         jmp *%eax
 109 .section ".text"
 110 relocated:
 111
 112 /*
 113  * Clear BSS
 114  */
 115         xorl %eax,%eax
 116         leal _edata(%ebx),%edi
 117         leal _end(%ebx), %ecx
 118         subl %edi,%ecx
 119         cld
 120         rep
 121         stosb
 122
 123 /*
 124  * Setup the stack for the decompressor
 125  */
 126         leal stack_end(%ebx), %esp
 127
 128 /*
 129  * Do the decompression, and jump to the new kernel..
 130  */
 131         movl output_len(%ebx), %eax
 132         pushl %eax
 133         pushl %ebp      # output address
 134         movl input_len(%ebx), %eax
 135         pushl %eax      # input_len
 136         leal input_data(%ebx), %eax
 137         pushl %eax      # input_data
 138         leal _end(%ebx), %eax
 139         pushl %eax      # end of the image as third argument
 140         pushl %esi      # real mode pointer as second arg
 141         call decompress_kernel
 142         addl $20, %esp
 143         popl %ecx
 144
 145 #if CONFIG_RELOCATABLE
 146 /* Find the address of the relocations.
 147  */
 148         movl %ebp, %edi
 149         addl %ecx, %edi
 150
 151 /* Calculate the delta between where vmlinux was compiled to run
 152  * and where it was actually loaded.
 153  */
 154         movl %ebp, %ebx
 155         subl $LOAD_PHYSICAL_ADDR, %ebx
 156         jz   2f         /* Nothing to be done if loaded at compiled addr. */
 157 /*
 158  * Process relocations.
 159  */
 160
 161 1:      subl $4, %edi
 162         movl 0(%edi), %ecx
 163         testl %ecx, %ecx
 164         jz 2f
 165         addl %ebx, -__PAGE_OFFSET(%ebx, %ecx)
 166         jmp 1b
 167 2:
 168 #endif
 169
 170 /*
 171  * Jump to the decompressed kernel.
 172  */
 173         xorl %ebx,%ebx
 174         jmp *%ebp
 175
 176 .bss
 177 .balign 4
 178 stack:
 179         .fill 4096, 1, 0
 180 stack_end: