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/*
 *  linux/boot/head.S
 *
 *  Copyright (C) 1991, 1992, 1993  Linus Torvalds
 */

/*
 *  head.S contains the 32-bit startup code.
 *
 * NOTE!!! Startup happens at absolute address 0x00001000, which is also where
 * the page directory will exist. The startup code will be overwritten by
 * the page directory. [According to comments etc elsewhere on a compressed
 * kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC]
 *
 * In SMP mode we keep this page safe. Really we ought to shuffle things and
 * put the trampoline here. - AC. An SMP trampoline enters with %cx holding
 * the stack base.
 *
 * Page 0 is deliberately kept safe, since System Management Mode code in 
 * laptops may need to access the BIOS data stored there.  This is also
 * useful for future device drivers that either access the BIOS via VM86 
 * mode.
 */

/*
 * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
 */
.text

#define __ASSEMBLY__
#include <linux/linkage.h>
#include <asm/segment.h>

        .globl startup_32
        
startup_32:
        cld
        cli
        movl $(KERNEL_DS),%eax
        mov %ax,%ds
        mov %ax,%es
        mov %ax,%fs
        mov %ax,%gs
#ifdef __SMP__
        orw %bx,%bx                     # What state are we in BX=1 for SMP
                                        # 0 for boot
        jz  2f                          # Initial boot

/*
 *      We are trampolining an SMP processor
 */
        mov %ax,%ss
        xorl %eax,%eax                  # Back to 0
        mov  %cx,%ax                    # SP low 16 bits
        movl %eax,%esp
        pushl 0                         # Clear NT
        popfl
        ljmp $(KERNEL_CS), $0x100000    # Into C and sanity

2:
#endif
        lss SYMBOL_NAME(stack_start),%esp
        xorl %eax,%eax
1:      incl %eax               # check that A20 really IS enabled
        movl %eax,0x000000      # loop forever if it isn't
        cmpl %eax,0x100000
        je 1b
/*
 * Initialize eflags.  Some BIOS's leave bits like NT set.  This would
 * confuse the debugger if this code is traced.
 * XXX - best to initialize before switching to protected mode.
 */
        pushl $0
        popfl
/*
 * Clear BSS
 */
        xorl %eax,%eax
        movl $ SYMBOL_NAME(_edata),%edi
        movl $ SYMBOL_NAME(_end),%ecx
        subl %edi,%ecx
        cld
        rep
        stosb
/*
 * Do the decompression, and jump to the new kernel..
 */
        subl $16,%esp   # place for structure on the stack
        pushl %esp      # address of structure as first arg
        call SYMBOL_NAME(decompress_kernel)
        orl  %eax,%eax 
        jnz  3f
        xorl %ebx,%ebx
        ljmp $(KERNEL_CS), $0x100000

/*
 * We come here, if we were loaded high.
 * We need to move the move-in-place routine down to 0x1000
 * and then start it with the buffer addresses in registers,
 * which we got from the stack.
 */
3:
        movl $move_routine_start,%esi
        movl $0x1000,%edi
        movl $move_routine_end,%ecx
        subl %esi,%ecx
        cld
        rep
        movsb

        popl %esi       # discard the address
        popl %esi       # low_buffer_start
        popl %ecx       # lcount
        popl %edx       # high_buffer_start
        popl %eax       # hcount
        movl $0x100000,%edi
        cli             # make sure we don't get interrupted
        ljmp $(KERNEL_CS), $0x1000 # and jump to the move routine

/*
 * Routine (template) for moving the decompressed kernel in place,
 * if we were high loaded. This _must_ PIC-code !
 */
move_routine_start:
        rep
        movsb
        movl %edx,%esi
        movl %eax,%ecx  # NOTE: rep movsb won't move if %ecx == 0
        rep
        movsb
        xorl %ebx,%ebx
/*
 * Well, the kernel relies on %esp pointing into low mem,
 * with the decompressor loaded high this is no longer true,
 * so we set esp here.
 */
        mov  $0x90000,%esp
        ljmp $(KERNEL_CS), $0x100000
move_routine_end: