1 /* 1 /*
2 * This file is subject to the terms and condi !! 2 * linux/boot/head.S
3 * License. See the file "COPYING" in the mai <<
4 * for more details. <<
5 * 3 *
6 * Copyright (C) 1994, 1995 Waldorf Electronic !! 4 * Copyright (C) 1991, 1992, 1993 Linus Torvalds
7 * Written by Ralf Baechle and Andreas Busse !! 5 */
8 * Copyright (C) 1995 - 1999 Ralf Baechle <<
9 * Copyright (C) 1996 Paul M. Antoine <<
10 * Modified for DECStation and hence R3000 sup <<
11 * Further modifications by David S. Miller an <<
12 * Copyright (C) 1999 Silicon Graphics, Inc. <<
13 */ <<
14 <<
15 #include <asm/asm.h> <<
16 #include <asm/regdef.h> <<
17 <<
18 LEAF(start) <<
19 /* Save boot rom start args */ <<
20 move s0, a0 <<
21 move s1, a1 <<
22 move s2, a2 <<
23 move s3, a3 <<
24 <<
25 /* Clear BSS */ <<
26 PTR_LA a0, _edata <<
27 PTR_LA a2, _end <<
28 1: PTR_S zero, 0(a0) <<
29 PTR_ADDIU a0, a0, PTRSIZE <<
30 bne a2, a0, 1b <<
31 <<
32 PTR_LA a0, (.heap) /* heap a <<
33 PTR_LA sp, (.stack + 8192) /* stack <<
34 <<
35 PTR_LA t9, decompress_kernel <<
36 jalr t9 <<
37 <<
38 2: <<
39 move a0, s0 <<
40 move a1, s1 <<
41 move a2, s2 <<
42 move a3, s3 <<
43 PTR_LI t9, KERNEL_ENTRY <<
44 jalr t9 <<
45 6
46 3: !! 7 /*
47 b 3b !! 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
48 25
49 END(start) !! 26 #include <linux/linkage.h>
>> 27 #include <asm/segment.h>
50 28
51 .comm .heap,BOOT_HEAP_SIZE,4 !! 29 .globl startup_32
52 .comm .stack,4096*2,4 !! 30
>> 31 startup_32:
>> 32 cld
>> 33 cli
>> 34 movl $(__KERNEL_DS),%eax
>> 35 movl %eax,%ds
>> 36 movl %eax,%es
>> 37 movl %eax,%fs
>> 38 movl %eax,%gs
>> 39
>> 40 lss SYMBOL_NAME(stack_start),%esp
>> 41 xorl %eax,%eax
>> 42 1: incl %eax # check that A20 really IS enabled
>> 43 movl %eax,0x000000 # loop forever if it isn't
>> 44 cmpl %eax,0x100000
>> 45 je 1b
>> 46
>> 47 /*
>> 48 * Initialize eflags. Some BIOS's leave bits like NT set. This would
>> 49 * confuse the debugger if this code is traced.
>> 50 * XXX - best to initialize before switching to protected mode.
>> 51 */
>> 52 pushl $0
>> 53 popfl
>> 54 /*
>> 55 * Clear BSS
>> 56 */
>> 57 xorl %eax,%eax
>> 58 movl $ SYMBOL_NAME(_edata),%edi
>> 59 movl $ SYMBOL_NAME(_end),%ecx
>> 60 subl %edi,%ecx
>> 61 cld
>> 62 rep
>> 63 stosb
>> 64 /*
>> 65 * Do the decompression, and jump to the new kernel..
>> 66 */
>> 67 subl $16,%esp # place for structure on the stack
>> 68 movl %esp,%eax
>> 69 pushl %esi # real mode pointer as second arg
>> 70 pushl %eax # address of structure as first arg
>> 71 call SYMBOL_NAME(decompress_kernel)
>> 72 orl %eax,%eax
>> 73 jnz 3f
>> 74 popl %esi # discard address
>> 75 popl %esi # real mode pointer
>> 76 xorl %ebx,%ebx
>> 77 ljmp $(__KERNEL_CS), $0x100000
>> 78
>> 79 /*
>> 80 * We come here, if we were loaded high.
>> 81 * We need to move the move-in-place routine down to 0x1000
>> 82 * and then start it with the buffer addresses in registers,
>> 83 * which we got from the stack.
>> 84 */
>> 85 3:
>> 86 movl $move_routine_start,%esi
>> 87 movl $0x1000,%edi
>> 88 movl $move_routine_end,%ecx
>> 89 subl %esi,%ecx
>> 90 addl $3,%ecx
>> 91 shrl $2,%ecx
>> 92 cld
>> 93 rep
>> 94 movsl
>> 95
>> 96 popl %esi # discard the address
>> 97 popl %ebx # real mode pointer
>> 98 popl %esi # low_buffer_start
>> 99 popl %ecx # lcount
>> 100 popl %edx # high_buffer_start
>> 101 popl %eax # hcount
>> 102 movl $0x100000,%edi
>> 103 cli # make sure we don't get interrupted
>> 104 ljmp $(__KERNEL_CS), $0x1000 # and jump to the move routine
>> 105
>> 106 /*
>> 107 * Routine (template) for moving the decompressed kernel in place,
>> 108 * if we were high loaded. This _must_ PIC-code !
>> 109 */
>> 110 move_routine_start:
>> 111 movl %ecx,%ebp
>> 112 shrl $2,%ecx
>> 113 rep
>> 114 movsl
>> 115 movl %ebp,%ecx
>> 116 andl $3,%ecx
>> 117 rep
>> 118 movsb
>> 119 movl %edx,%esi
>> 120 movl %eax,%ecx # NOTE: rep movsb won't move if %ecx == 0
>> 121 addl $3,%ecx
>> 122 shrl $2,%ecx
>> 123 rep
>> 124 movsl
>> 125 movl %ebx,%esi # Restore setup pointer
>> 126 xorl %ebx,%ebx
>> 127 ljmp $(__KERNEL_CS), $0x100000
>> 128 move_routine_end:
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