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/linkage.h> 27#include <asm/segment.h> 28#include <asm/page_types.h> 29#include <asm/boot.h> 30#include <asm/asm-offsets.h> 31 32 .section ".text.head","ax",@progbits 33ENTRY(startup_32) 34 cld 35 /* 36 * Test KEEP_SEGMENTS flag to see if the bootloader is asking 37 * us to not reload segments 38 */ 39 testb $(1<<6), BP_loadflags(%esi) 40 jnz 1f 41 42 cli 43 movl $__BOOT_DS, %eax 44 movl %eax, %ds 45 movl %eax, %es 46 movl %eax, %fs 47 movl %eax, %gs 48 movl %eax, %ss 491: 50 51/* 52 * Calculate the delta between where we were compiled to run 53 * at and where we were actually loaded at. This can only be done 54 * with a short local call on x86. Nothing else will tell us what 55 * address we are running at. The reserved chunk of the real-mode 56 * data at 0x1e4 (defined as a scratch field) are used as the stack 57 * for this calculation. Only 4 bytes are needed. 58 */ 59 leal (BP_scratch+4)(%esi), %esp 60 call 1f 611: popl %ebp 62 subl $1b, %ebp 63 64/* 65 * %ebp contains the address we are loaded at by the boot loader and %ebx 66 * contains the address where we should move the kernel image temporarily 67 * for safe in-place decompression. 68 */ 69 70#ifdef CONFIG_RELOCATABLE 71 movl %ebp, %ebx 72 movl BP_kernel_alignment(%esi), %eax 73 decl %eax 74 addl %eax, %ebx 75 notl %eax 76 andl %eax, %ebx 77#else 78 movl $LOAD_PHYSICAL_ADDR, %ebx 79#endif 80 81 /* Target address to relocate to for decompression */ 82 addl $z_extract_offset, %ebx 83 84 /* Set up the stack */ 85 leal boot_stack_end(%ebx), %esp 86 87 /* Zero EFLAGS */ 88 pushl $0 89 popfl 90 91/* 92 * Copy the compressed kernel to the end of our buffer 93 * where decompression in place becomes safe. 94 */ 95 pushl %esi 96 leal (_bss-4)(%ebp), %esi 97 leal (_bss-4)(%ebx), %edi 98 movl $(_bss - startup_32), %ecx 99 shrl $2, %ecx 100 std 101 rep movsl 102 cld 103 popl %esi 104 105/* 106 * Jump to the relocated address. 107 */ 108 leal relocated(%ebx), %eax 109 jmp *%eax 110ENDPROC(startup_32) 111 112 .text 113relocated: 114 115/* 116 * Clear BSS (stack is currently empty) 117 */ 118 xorl %eax, %eax 119 leal _bss(%ebx), %edi 120 leal _ebss(%ebx), %ecx 121 subl %edi, %ecx 122 shrl $2, %ecx 123 rep stosl 124 125/* 126 * Do the decompression, and jump to the new kernel.. 127 */ 128 leal z_extract_offset_negative(%ebx), %ebp 129 /* push arguments for decompress_kernel: */ 130 pushl %ebp /* output address */ 131 pushl $z_input_len /* input_len */ 132 leal input_data(%ebx), %eax 133 pushl %eax /* input_data */ 134 leal boot_heap(%ebx), %eax 135 pushl %eax /* heap area */ 136 pushl %esi /* real mode pointer */ 137 call decompress_kernel 138 addl $20, %esp 139 140#if CONFIG_RELOCATABLE 141/* 142 * Find the address of the relocations. 143 */ 144 leal z_output_len(%ebp), %edi 145 146/* 147 * Calculate the delta between where vmlinux was compiled to run 148 * and where it was actually loaded. 149 */ 150 movl %ebp, %ebx 151 subl $LOAD_PHYSICAL_ADDR, %ebx 152 jz 2f /* Nothing to be done if loaded at compiled addr. */ 153/* 154 * Process relocations. 155 */ 156 1571: subl $4, %edi 158 movl (%edi), %ecx 159 testl %ecx, %ecx 160 jz 2f 161 addl %ebx, -__PAGE_OFFSET(%ebx, %ecx) 162 jmp 1b 1632: 164#endif 165 166/* 167 * Jump to the decompressed kernel. 168 */ 169 xorl %ebx, %ebx 170 jmp *%ebp 171 172/* 173 * Stack and heap for uncompression 174 */ 175 .bss 176 .balign 4 177boot_heap: 178 .fill BOOT_HEAP_SIZE, 1, 0 179boot_stack: 180 .fill BOOT_STACK_SIZE, 1, 0 181boot_stack_end: 182