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#include <asm/bootparam.h> 33 34/* 35 * The 32-bit x86 assembler in binutils 2.26 will generate R_386_GOT32X 36 * relocation to get the symbol address in PIC. When the compressed x86 37 * kernel isn't built as PIC, the linker optimizes R_386_GOT32X 38 * relocations to their fixed symbol addresses. However, when the 39 * compressed x86 kernel is loaded at a different address, it leads 40 * to the following load failure: 41 * 42 * Failed to allocate space for phdrs 43 * 44 * during the decompression stage. 45 * 46 * If the compressed x86 kernel is relocatable at run-time, it should be 47 * compiled with -fPIE, instead of -fPIC, if possible and should be built as 48 * Position Independent Executable (PIE) so that linker won't optimize 49 * R_386_GOT32X relocation to its fixed symbol address. Older 50 * linkers generate R_386_32 relocations against locally defined symbols, 51 * _bss, _ebss, _got and _egot, in PIE. It isn't wrong, just less 52 * optimal than R_386_RELATIVE. But the x86 kernel fails to properly handle 53 * R_386_32 relocations when relocating the kernel. To generate 54 * R_386_RELATIVE relocations, we mark _bss, _ebss, _got and _egot as 55 * hidden: 56 */ 57 .hidden _bss 58 .hidden _ebss 59 .hidden _got 60 .hidden _egot 61 62 __HEAD 63ENTRY(startup_32) 64#ifdef CONFIG_EFI_STUB 65 jmp preferred_addr 66 67 /* 68 * We don't need the return address, so set up the stack so 69 * efi_main() can find its arguments. 70 */ 71ENTRY(efi_pe_entry) 72 add $0x4, %esp 73 74 call 1f 751: popl %esi 76 subl $1b, %esi 77 78 popl %ecx 79 movl %ecx, efi32_config(%esi) /* Handle */ 80 popl %ecx 81 movl %ecx, efi32_config+8(%esi) /* EFI System table pointer */ 82 83 /* Relocate efi_config->call() */ 84 leal efi32_config(%esi), %eax 85 add %esi, 88(%eax) 86 pushl %eax 87 88 call make_boot_params 89 cmpl $0, %eax 90 je fail 91 movl %esi, BP_code32_start(%eax) 92 popl %ecx 93 pushl %eax 94 pushl %ecx 95 jmp 2f /* Skip efi_config initialization */ 96 97ENTRY(efi32_stub_entry) 98 add $0x4, %esp 99 popl %ecx 100 popl %edx 101 102 call 1f 1031: popl %esi 104 subl $1b, %esi 105 106 movl %ecx, efi32_config(%esi) /* Handle */ 107 movl %edx, efi32_config+8(%esi) /* EFI System table pointer */ 108 109 /* Relocate efi_config->call() */ 110 leal efi32_config(%esi), %eax 111 add %esi, 88(%eax) 112 pushl %eax 1132: 114 call efi_main 115 cmpl $0, %eax 116 movl %eax, %esi 117 jne 2f 118fail: 119 /* EFI init failed, so hang. */ 120 hlt 121 jmp fail 1222: 123 movl BP_code32_start(%esi), %eax 124 leal preferred_addr(%eax), %eax 125 jmp *%eax 126 127preferred_addr: 128#endif 129 cld 130 /* 131 * Test KEEP_SEGMENTS flag to see if the bootloader is asking 132 * us to not reload segments 133 */ 134 testb $KEEP_SEGMENTS, BP_loadflags(%esi) 135 jnz 1f 136 137 cli 138 movl $__BOOT_DS, %eax 139 movl %eax, %ds 140 movl %eax, %es 141 movl %eax, %fs 142 movl %eax, %gs 143 movl %eax, %ss 1441: 145 146/* 147 * Calculate the delta between where we were compiled to run 148 * at and where we were actually loaded at. This can only be done 149 * with a short local call on x86. Nothing else will tell us what 150 * address we are running at. The reserved chunk of the real-mode 151 * data at 0x1e4 (defined as a scratch field) are used as the stack 152 * for this calculation. Only 4 bytes are needed. 153 */ 154 leal (BP_scratch+4)(%esi), %esp 155 call 1f 1561: popl %ebp 157 subl $1b, %ebp 158 159/* 160 * %ebp contains the address we are loaded at by the boot loader and %ebx 161 * contains the address where we should move the kernel image temporarily 162 * for safe in-place decompression. 163 */ 164 165#ifdef CONFIG_RELOCATABLE 166 movl %ebp, %ebx 167 movl BP_kernel_alignment(%esi), %eax 168 decl %eax 169 addl %eax, %ebx 170 notl %eax 171 andl %eax, %ebx 172 cmpl $LOAD_PHYSICAL_ADDR, %ebx 173 jge 1f 174#endif 175 movl $LOAD_PHYSICAL_ADDR, %ebx 1761: 177 178 /* Target address to relocate to for decompression */ 179 movl BP_init_size(%esi), %eax 180 subl $_end, %eax 181 addl %eax, %ebx 182 183 /* Set up the stack */ 184 leal boot_stack_end(%ebx), %esp 185 186 /* Zero EFLAGS */ 187 pushl $0 188 popfl 189 190/* 191 * Copy the compressed kernel to the end of our buffer 192 * where decompression in place becomes safe. 193 */ 194 pushl %esi 195 leal (_bss-4)(%ebp), %esi 196 leal (_bss-4)(%ebx), %edi 197 movl $(_bss - startup_32), %ecx 198 shrl $2, %ecx 199 std 200 rep movsl 201 cld 202 popl %esi 203 204/* 205 * Jump to the relocated address. 206 */ 207 leal relocated(%ebx), %eax 208 jmp *%eax 209ENDPROC(startup_32) 210 211 .text 212relocated: 213 214/* 215 * Clear BSS (stack is currently empty) 216 */ 217 xorl %eax, %eax 218 leal _bss(%ebx), %edi 219 leal _ebss(%ebx), %ecx 220 subl %edi, %ecx 221 shrl $2, %ecx 222 rep stosl 223 224/* 225 * Adjust our own GOT 226 */ 227 leal _got(%ebx), %edx 228 leal _egot(%ebx), %ecx 2291: 230 cmpl %ecx, %edx 231 jae 2f 232 addl %ebx, (%edx) 233 addl $4, %edx 234 jmp 1b 2352: 236 237/* 238 * Do the extraction, and jump to the new kernel.. 239 */ 240 /* push arguments for extract_kernel: */ 241 pushl $z_output_len /* decompressed length, end of relocs */ 242 243 movl BP_init_size(%esi), %eax 244 subl $_end, %eax 245 movl %ebx, %ebp 246 subl %eax, %ebp 247 pushl %ebp /* output address */ 248 249 pushl $z_input_len /* input_len */ 250 leal input_data(%ebx), %eax 251 pushl %eax /* input_data */ 252 leal boot_heap(%ebx), %eax 253 pushl %eax /* heap area */ 254 pushl %esi /* real mode pointer */ 255 call extract_kernel /* returns kernel location in %eax */ 256 addl $24, %esp 257 258/* 259 * Jump to the extracted kernel. 260 */ 261 xorl %ebx, %ebx 262 jmp *%eax 263 264#ifdef CONFIG_EFI_STUB 265 .data 266efi32_config: 267 .fill 11,8,0 268 .long efi_call_phys 269 .long 0 270 .byte 0 271#endif 272 273/* 274 * Stack and heap for uncompression 275 */ 276 .bss 277 .balign 4 278boot_heap: 279 .fill BOOT_HEAP_SIZE, 1, 0 280boot_stack: 281 .fill BOOT_STACK_SIZE, 1, 0 282boot_stack_end: 283