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/init.h> 27#include <linux/linkage.h> 28#include <asm/segment.h> 29#include <asm/page_types.h> 30#include <asm/boot.h> 31#include <asm/asm-offsets.h> 32 33 __HEAD 34ENTRY(startup_32) 35#ifdef CONFIG_EFI_STUB 36 jmp preferred_addr 37 38 .balign 0x10 39 /* 40 * We don't need the return address, so set up the stack so 41 * efi_main() can find its arugments. 42 */ 43 add $0x4, %esp 44 45 call make_boot_params 46 cmpl $0, %eax 47 je 1f 48 movl 0x4(%esp), %esi 49 movl (%esp), %ecx 50 pushl %eax 51 pushl %esi 52 pushl %ecx 53 54 .org 0x30,0x90 55 call efi_main 56 cmpl $0, %eax 57 movl %eax, %esi 58 jne 2f 591: 60 /* EFI init failed, so hang. */ 61 hlt 62 jmp 1b 632: 64 call 3f 653: 66 popl %eax 67 subl $3b, %eax 68 subl BP_pref_address(%esi), %eax 69 add BP_code32_start(%esi), %eax 70 leal preferred_addr(%eax), %eax 71 jmp *%eax 72 73preferred_addr: 74#endif 75 cld 76 /* 77 * Test KEEP_SEGMENTS flag to see if the bootloader is asking 78 * us to not reload segments 79 */ 80 testb $(1<<6), BP_loadflags(%esi) 81 jnz 1f 82 83 cli 84 movl $__BOOT_DS, %eax 85 movl %eax, %ds 86 movl %eax, %es 87 movl %eax, %fs 88 movl %eax, %gs 89 movl %eax, %ss 901: 91 92/* 93 * Calculate the delta between where we were compiled to run 94 * at and where we were actually loaded at. This can only be done 95 * with a short local call on x86. Nothing else will tell us what 96 * address we are running at. The reserved chunk of the real-mode 97 * data at 0x1e4 (defined as a scratch field) are used as the stack 98 * for this calculation. Only 4 bytes are needed. 99 */ 100 leal (BP_scratch+4)(%esi), %esp 101 call 1f 1021: popl %ebp 103 subl $1b, %ebp 104 105/* 106 * %ebp contains the address we are loaded at by the boot loader and %ebx 107 * contains the address where we should move the kernel image temporarily 108 * for safe in-place decompression. 109 */ 110 111#ifdef CONFIG_RELOCATABLE 112 movl %ebp, %ebx 113 movl BP_kernel_alignment(%esi), %eax 114 decl %eax 115 addl %eax, %ebx 116 notl %eax 117 andl %eax, %ebx 118#else 119 movl $LOAD_PHYSICAL_ADDR, %ebx 120#endif 121 122 /* Target address to relocate to for decompression */ 123 addl $z_extract_offset, %ebx 124 125 /* Set up the stack */ 126 leal boot_stack_end(%ebx), %esp 127 128 /* Zero EFLAGS */ 129 pushl $0 130 popfl 131 132/* 133 * Copy the compressed kernel to the end of our buffer 134 * where decompression in place becomes safe. 135 */ 136 pushl %esi 137 leal (_bss-4)(%ebp), %esi 138 leal (_bss-4)(%ebx), %edi 139 movl $(_bss - startup_32), %ecx 140 shrl $2, %ecx 141 std 142 rep movsl 143 cld 144 popl %esi 145 146/* 147 * Jump to the relocated address. 148 */ 149 leal relocated(%ebx), %eax 150 jmp *%eax 151ENDPROC(startup_32) 152 153 .text 154relocated: 155 156/* 157 * Clear BSS (stack is currently empty) 158 */ 159 xorl %eax, %eax 160 leal _bss(%ebx), %edi 161 leal _ebss(%ebx), %ecx 162 subl %edi, %ecx 163 shrl $2, %ecx 164 rep stosl 165 166/* 167 * Adjust our own GOT 168 */ 169 leal _got(%ebx), %edx 170 leal _egot(%ebx), %ecx 1711: 172 cmpl %ecx, %edx 173 jae 2f 174 addl %ebx, (%edx) 175 addl $4, %edx 176 jmp 1b 1772: 178 179/* 180 * Do the decompression, and jump to the new kernel.. 181 */ 182 leal z_extract_offset_negative(%ebx), %ebp 183 /* push arguments for decompress_kernel: */ 184 pushl %ebp /* output address */ 185 pushl $z_input_len /* input_len */ 186 leal input_data(%ebx), %eax 187 pushl %eax /* input_data */ 188 leal boot_heap(%ebx), %eax 189 pushl %eax /* heap area */ 190 pushl %esi /* real mode pointer */ 191 call decompress_kernel 192 addl $20, %esp 193 194#if CONFIG_RELOCATABLE 195/* 196 * Find the address of the relocations. 197 */ 198 leal z_output_len(%ebp), %edi 199 200/* 201 * Calculate the delta between where vmlinux was compiled to run 202 * and where it was actually loaded. 203 */ 204 movl %ebp, %ebx 205 subl $LOAD_PHYSICAL_ADDR, %ebx 206 jz 2f /* Nothing to be done if loaded at compiled addr. */ 207/* 208 * Process relocations. 209 */ 210 2111: subl $4, %edi 212 movl (%edi), %ecx 213 testl %ecx, %ecx 214 jz 2f 215 addl %ebx, -__PAGE_OFFSET(%ebx, %ecx) 216 jmp 1b 2172: 218#endif 219 220/* 221 * Jump to the decompressed kernel. 222 */ 223 xorl %ebx, %ebx 224 jmp *%ebp 225 226/* 227 * Stack and heap for uncompression 228 */ 229 .bss 230 .balign 4 231boot_heap: 232 .fill BOOT_HEAP_SIZE, 1, 0 233boot_stack: 234 .fill BOOT_STACK_SIZE, 1, 0 235boot_stack_end: 236