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 /* 39 * We don't need the return address, so set up the stack so 40 * efi_main() can find its arguments. 41 */ 42ENTRY(efi_pe_entry) 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 sub $0x4, %esp 54 55ENTRY(efi_stub_entry) 56 add $0x4, %esp 57 call efi_main 58 cmpl $0, %eax 59 movl %eax, %esi 60 jne 2f 611: 62 /* EFI init failed, so hang. */ 63 hlt 64 jmp 1b 652: 66 call 3f 673: 68 popl %eax 69 subl $3b, %eax 70 subl BP_pref_address(%esi), %eax 71 add BP_code32_start(%esi), %eax 72 leal preferred_addr(%eax), %eax 73 jmp *%eax 74 75preferred_addr: 76#endif 77 cld 78 /* 79 * Test KEEP_SEGMENTS flag to see if the bootloader is asking 80 * us to not reload segments 81 */ 82 testb $(1<<6), BP_loadflags(%esi) 83 jnz 1f 84 85 cli 86 movl $__BOOT_DS, %eax 87 movl %eax, %ds 88 movl %eax, %es 89 movl %eax, %fs 90 movl %eax, %gs 91 movl %eax, %ss 921: 93 94/* 95 * Calculate the delta between where we were compiled to run 96 * at and where we were actually loaded at. This can only be done 97 * with a short local call on x86. Nothing else will tell us what 98 * address we are running at. The reserved chunk of the real-mode 99 * data at 0x1e4 (defined as a scratch field) are used as the stack 100 * for this calculation. Only 4 bytes are needed. 101 */ 102 leal (BP_scratch+4)(%esi), %esp 103 call 1f 1041: popl %ebp 105 subl $1b, %ebp 106 107/* 108 * %ebp contains the address we are loaded at by the boot loader and %ebx 109 * contains the address where we should move the kernel image temporarily 110 * for safe in-place decompression. 111 */ 112 113#ifdef CONFIG_RELOCATABLE 114 movl %ebp, %ebx 115 movl BP_kernel_alignment(%esi), %eax 116 decl %eax 117 addl %eax, %ebx 118 notl %eax 119 andl %eax, %ebx 120 cmpl $LOAD_PHYSICAL_ADDR, %ebx 121 jge 1f 122#endif 123 movl $LOAD_PHYSICAL_ADDR, %ebx 1241: 125 126 /* Target address to relocate to for decompression */ 127 addl $z_extract_offset, %ebx 128 129 /* Set up the stack */ 130 leal boot_stack_end(%ebx), %esp 131 132 /* Zero EFLAGS */ 133 pushl $0 134 popfl 135 136/* 137 * Copy the compressed kernel to the end of our buffer 138 * where decompression in place becomes safe. 139 */ 140 pushl %esi 141 leal (_bss-4)(%ebp), %esi 142 leal (_bss-4)(%ebx), %edi 143 movl $(_bss - startup_32), %ecx 144 shrl $2, %ecx 145 std 146 rep movsl 147 cld 148 popl %esi 149 150/* 151 * Jump to the relocated address. 152 */ 153 leal relocated(%ebx), %eax 154 jmp *%eax 155ENDPROC(startup_32) 156 157 .text 158relocated: 159 160/* 161 * Clear BSS (stack is currently empty) 162 */ 163 xorl %eax, %eax 164 leal _bss(%ebx), %edi 165 leal _ebss(%ebx), %ecx 166 subl %edi, %ecx 167 shrl $2, %ecx 168 rep stosl 169 170/* 171 * Adjust our own GOT 172 */ 173 leal _got(%ebx), %edx 174 leal _egot(%ebx), %ecx 1751: 176 cmpl %ecx, %edx 177 jae 2f 178 addl %ebx, (%edx) 179 addl $4, %edx 180 jmp 1b 1812: 182 183/* 184 * Do the decompression, and jump to the new kernel.. 185 */ 186 /* push arguments for decompress_kernel: */ 187 pushl $z_output_len /* decompressed length */ 188 leal z_extract_offset_negative(%ebx), %ebp 189 pushl %ebp /* output address */ 190 pushl $z_input_len /* input_len */ 191 leal input_data(%ebx), %eax 192 pushl %eax /* input_data */ 193 leal boot_heap(%ebx), %eax 194 pushl %eax /* heap area */ 195 pushl %esi /* real mode pointer */ 196 call decompress_kernel /* returns kernel location in %eax */ 197 addl $24, %esp 198 199/* 200 * Jump to the decompressed kernel. 201 */ 202 xorl %ebx, %ebx 203 jmp *%eax 204 205/* 206 * Stack and heap for uncompression 207 */ 208 .bss 209 .balign 4 210boot_heap: 211 .fill BOOT_HEAP_SIZE, 1, 0 212boot_stack: 213 .fill BOOT_STACK_SIZE, 1, 0 214boot_stack_end: 215