root/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  * In SMP mode we keep this page safe. Really we ought to shuffle things and
  16  * put the trampoline here. - AC. An SMP trampoline enters with %cx holding
  17  * the stack base.
  18  *
  19  * Page 0 is deliberately kept safe, since System Management Mode code in 
  20  * laptops may need to access the BIOS data stored there.  This is also
  21  * useful for future device drivers that either access the BIOS via VM86 
  22  * mode.
  23  */
  24 
  25 /*
  26  * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
  27  */
  28 .text
  29 
  30 #define __ASSEMBLY__
  31 #include <linux/config.h>
  32 #include <linux/linkage.h>
  33 #include <asm/segment.h>
  34 
  35         .globl startup_32
  36         
  37 startup_32:
  38         cld
  39         cli
  40         movl $(KERNEL_DS),%eax
  41         mov %ax,%ds
  42         mov %ax,%es
  43         mov %ax,%fs
  44         mov %ax,%gs
  45 #ifdef __SMP__
  46         orw %bx,%bx                     # What state are we in BX=1 for SMP
  47                                         # 0 for boot
  48         jz  2f                          # Initial boot
  49 
  50 /*
  51  *      We are trampolining an SMP processor
  52  */
  53         mov %ax,%ss
  54         xorl %eax,%eax                  # Back to 0
  55         mov  %cx,%ax                    # SP low 16 bits
  56         movl %eax,%esp
  57         pushl 0                         # Clear NT
  58         popfl
  59         ljmp $(KERNEL_CS), $0x100000    # Into C and sanity
  60 
  61 2:
  62 #endif
  63         lss SYMBOL_NAME(stack_start),%esp
  64         xorl %eax,%eax
  65 1:      incl %eax               # check that A20 really IS enabled
  66         movl %eax,0x000000      # loop forever if it isn't
  67         cmpl %eax,0x100000
  68         je 1b
  69 /*
  70  * Initialize eflags.  Some BIOS's leave bits like NT set.  This would
  71  * confuse the debugger if this code is traced.
  72  * XXX - best to initialize before switching to protected mode.
  73  */
  74         pushl $0
  75         popfl
  76 /*
  77  * Clear BSS
  78  */
  79         xorl %eax,%eax
  80         movl $ SYMBOL_NAME(_edata),%edi
  81         movl $ SYMBOL_NAME(_end),%ecx
  82         subl %edi,%ecx
  83         cld
  84         rep
  85         stosb
  86 /*
  87  * Do the decompression, and jump to the new kernel..
  88  */
  89         subl $16,%esp   # place for structure on the stack
  90         pushl %esp      # address of structure as first arg
  91         call SYMBOL_NAME(decompress_kernel)
  92         orl  %eax,%eax 
  93         jnz  3f
  94         xorl %ebx,%ebx
  95         ljmp $(KERNEL_CS), $0x100000
  96 
  97 /*
  98  * We come here, if we were loaded high.
  99  * We need to move the move-in-place routine down to 0x1000
 100  * and then start it with the buffer addresses in registers,
 101  * which we got from the stack.
 102  */
 103 3:
 104         movl $move_routine_start,%esi
 105         movl $0x1000,%edi
 106         movl $move_routine_end,%ecx
 107         subl %esi,%ecx
 108         cld
 109         rep
 110         movsb
 111 
 112         popl %esi       # discard the address
 113         popl %esi       # low_buffer_start
 114         popl %ecx       # lcount
 115         popl %edx       # high_buffer_start
 116         popl %eax       # hcount
 117         movl $0x100000,%edi
 118         cli             # make sure we don't get interrupted
 119         ljmp $(KERNEL_CS), $0x1000 # and jump to the move routine
 120 
 121 /*
 122  * Routine (template) for moving the decompressed kernel in place,
 123  * if we were high loaded. This _must_ PIC-code !
 124  */
 125 move_routine_start:
 126         rep
 127         movsb
 128         movl %edx,%esi
 129         movl %eax,%ecx  # NOTE: rep movsb won't move if %ecx == 0
 130         rep
 131         movsb
 132         xorl %ebx,%ebx
 133 /*
 134  * Well, the kernel relies on %esp pointing into low mem,
 135  * with the decompressor loaded high this is no longer true,
 136  * so we set esp here.
 137  */
 138         mov  $0x90000,%esp
 139         ljmp $(KERNEL_CS), $0x100000
 140 move_routine_end:

/* */