arch/x86/boot/compressed/head_32.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/init.h>
  27 #include <linux/linkage.h>
  28 #include <asm/segment.h>
  29 #include <asm/page_types.h>
  30 #include <asm/boot.h>
  31 #include <asm/asm-offsets.h>
  32
  33         __HEAD
  34 ENTRY(startup_32)
  35 #ifdef CONFIG_EFI_STUB
  36         jmp     preferred_addr
  37
  38         .balign 0x10
  39         /*
  40          * We don't need the return address, so set up the stack so
  41          * efi_main() can find its arugments.
  42          */
  43         add     $0x4, %esp
  44
  45         call    efi_main
  46         cmpl    $0, %eax
  47         movl    %eax, %esi
  48         jne     2f
  49 1:
  50         /* EFI init failed, so hang. */
  51         hlt
  52         jmp     1b
  53 2:
  54         call    3f
  55 3:
  56         popl    %eax
  57         subl    $3b, %eax
  58         subl    BP_pref_address(%esi), %eax
  59         add     BP_code32_start(%esi), %eax
  60         leal    preferred_addr(%eax), %eax
  61         jmp     *%eax
  62
  63 preferred_addr:
  64 #endif
  65         cld
  66         /*
  67          * Test KEEP_SEGMENTS flag to see if the bootloader is asking
  68          * us to not reload segments
  69          */
  70         testb   $(1<<6), BP_loadflags(%esi)
  71         jnz     1f
  72
  73         cli
  74         movl    $__BOOT_DS, %eax
  75         movl    %eax, %ds
  76         movl    %eax, %es
  77         movl    %eax, %fs
  78         movl    %eax, %gs
  79         movl    %eax, %ss
  80 1:
  81
  82 /*
  83  * Calculate the delta between where we were compiled to run
  84  * at and where we were actually loaded at.  This can only be done
  85  * with a short local call on x86.  Nothing  else will tell us what
  86  * address we are running at.  The reserved chunk of the real-mode
  87  * data at 0x1e4 (defined as a scratch field) are used as the stack
  88  * for this calculation. Only 4 bytes are needed.
  89  */
  90         leal    (BP_scratch+4)(%esi), %esp
  91         call    1f
  92 1:      popl    %ebp
  93         subl    $1b, %ebp
  94
  95 /*
  96  * %ebp contains the address we are loaded at by the boot loader and %ebx
  97  * contains the address where we should move the kernel image temporarily
  98  * for safe in-place decompression.
  99  */
 100
 101 #ifdef CONFIG_RELOCATABLE
 102         movl    %ebp, %ebx
 103         movl    BP_kernel_alignment(%esi), %eax
 104         decl    %eax
 105         addl    %eax, %ebx
 106         notl    %eax
 107         andl    %eax, %ebx
 108 #else
 109         movl    $LOAD_PHYSICAL_ADDR, %ebx
 110 #endif
 111
 112         /* Target address to relocate to for decompression */
 113         addl    $z_extract_offset, %ebx
 114
 115         /* Set up the stack */
 116         leal    boot_stack_end(%ebx), %esp
 117
 118         /* Zero EFLAGS */
 119         pushl   $0
 120         popfl
 121
 122 /*
 123  * Copy the compressed kernel to the end of our buffer
 124  * where decompression in place becomes safe.
 125  */
 126         pushl   %esi
 127         leal    (_bss-4)(%ebp), %esi
 128         leal    (_bss-4)(%ebx), %edi
 129         movl    $(_bss - startup_32), %ecx
 130         shrl    $2, %ecx
 131         std
 132         rep     movsl
 133         cld
 134         popl    %esi
 135
 136 /*
 137  * Jump to the relocated address.
 138  */
 139         leal    relocated(%ebx), %eax
 140         jmp     *%eax
 141 ENDPROC(startup_32)
 142
 143         .text
 144 relocated:
 145
 146 /*
 147  * Clear BSS (stack is currently empty)
 148  */
 149         xorl    %eax, %eax
 150         leal    _bss(%ebx), %edi
 151         leal    _ebss(%ebx), %ecx
 152         subl    %edi, %ecx
 153         shrl    $2, %ecx
 154         rep     stosl
 155
 156 /*
 157  * Adjust our own GOT
 158  */
 159         leal    _got(%ebx), %edx
 160         leal    _egot(%ebx), %ecx
 161 1:
 162         cmpl    %ecx, %edx
 163         jae     2f
 164         addl    %ebx, (%edx)
 165         addl    $4, %edx
 166         jmp     1b
 167 2:
 168
 169 /*
 170  * Do the decompression, and jump to the new kernel..
 171  */
 172         leal    z_extract_offset_negative(%ebx), %ebp
 173                                 /* push arguments for decompress_kernel: */
 174         pushl   %ebp            /* output address */
 175         pushl   $z_input_len    /* input_len */
 176         leal    input_data(%ebx), %eax
 177         pushl   %eax            /* input_data */
 178         leal    boot_heap(%ebx), %eax
 179         pushl   %eax            /* heap area */
 180         pushl   %esi            /* real mode pointer */
 181         call    decompress_kernel
 182         addl    $20, %esp
 183
 184 #if CONFIG_RELOCATABLE
 185 /*
 186  * Find the address of the relocations.
 187  */
 188         leal    z_output_len(%ebp), %edi
 189
 190 /*
 191  * Calculate the delta between where vmlinux was compiled to run
 192  * and where it was actually loaded.
 193  */
 194         movl    %ebp, %ebx
 195         subl    $LOAD_PHYSICAL_ADDR, %ebx
 196         jz      2f      /* Nothing to be done if loaded at compiled addr. */
 197 /*
 198  * Process relocations.
 199  */
 200
 201 1:      subl    $4, %edi
 202         movl    (%edi), %ecx
 203         testl   %ecx, %ecx
 204         jz      2f
 205         addl    %ebx, -__PAGE_OFFSET(%ebx, %ecx)
 206         jmp     1b
 207 2:
 208 #endif
 209
 210 /*
 211  * Jump to the decompressed kernel.
 212  */
 213         xorl    %ebx, %ebx
 214         jmp     *%ebp
 215
 216 /*
 217  * Stack and heap for uncompression
 218  */
 219         .bss
 220         .balign 4
 221 boot_heap:
 222         .fill BOOT_HEAP_SIZE, 1, 0
 223 boot_stack:
 224         .fill BOOT_STACK_SIZE, 1, 0
 225 boot_stack_end: