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/*
 *  linux/boot/head.S
 *
 *  Copyright (C) 1991, 1992, 1993  Linus Torvalds
 *
 *  $Id: head.S,v 1.1.1.1 2004-04-15 01:36:30 phoenix Exp $                     
 */

/*
 *  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]
 *
 * 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     
 */
.code32
.text

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

        .code32
        .globl startup_32
        
startup_32:
        cld
        cli
        movl $(__KERNEL_DS),%eax
        movl %eax,%ds
        movl %eax,%es
        movl %eax,%fs
        movl %eax,%gs

        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
        movl %esp,%eax
        pushl %esi      # real mode pointer as second arg
        pushl %eax      # address of structure as first arg
        call SYMBOL_NAME(decompress_kernel)
        orl  %eax,%eax 
        jnz  3f
        addl $8,%esp
        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 %esi,%ebx  
        movl $move_routine_start,%esi
        movl $0x1000,%edi
        movl $move_routine_end,%ecx
        subl %esi,%ecx
        addl $3,%ecx
        shrl $2,%ecx
        cld
        rep
        movsl

        popl %esi       # discard the address
        addl $4,%esp    # real mode pointer
        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:
        movl %ecx,%ebp
        shrl $2,%ecx
        rep
        movsl
        movl %ebp,%ecx
        andl $3,%ecx
        rep
        movsb
        movl %edx,%esi
        movl %eax,%ecx  # NOTE: rep movsb won't move if %ecx == 0
        addl $3,%ecx
        shrl $2,%ecx
        rep
        movsl
        movl %ebx,%esi  # Restore setup pointer
        xorl %ebx,%ebx
        ljmp $(__KERNEL_CS), $0x100000
move_routine_end:


/* Stack for uncompression */   
        .align 32
user_stack:             
        .fill 4096,4,0
stack_start:    
        .long user_stack+4096
        .word __KERNEL_DS