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 .code32 25 .text 26 27#include <linux/init.h> 28#include <linux/linkage.h> 29#include <asm/segment.h> 30#include <asm/boot.h> 31#include <asm/msr.h> 32#include <asm/processor-flags.h> 33#include <asm/asm-offsets.h> 34 35 __HEAD 36 .code32 37ENTRY(startup_32) 38 /* 39 * 32bit entry is 0 and it is ABI so immutable! 40 * If we come here directly from a bootloader, 41 * kernel(text+data+bss+brk) ramdisk, zero_page, command line 42 * all need to be under the 4G limit. 43 */ 44 cld 45 /* 46 * Test KEEP_SEGMENTS flag to see if the bootloader is asking 47 * us to not reload segments 48 */ 49 testb $(1<<6), BP_loadflags(%esi) 50 jnz 1f 51 52 cli 53 movl $(__BOOT_DS), %eax 54 movl %eax, %ds 55 movl %eax, %es 56 movl %eax, %ss 571: 58 59/* 60 * Calculate the delta between where we were compiled to run 61 * at and where we were actually loaded at. This can only be done 62 * with a short local call on x86. Nothing else will tell us what 63 * address we are running at. The reserved chunk of the real-mode 64 * data at 0x1e4 (defined as a scratch field) are used as the stack 65 * for this calculation. Only 4 bytes are needed. 66 */ 67 leal (BP_scratch+4)(%esi), %esp 68 call 1f 691: popl %ebp 70 subl $1b, %ebp 71 72/* setup a stack and make sure cpu supports long mode. */ 73 movl $boot_stack_end, %eax 74 addl %ebp, %eax 75 movl %eax, %esp 76 77 call verify_cpu 78 testl %eax, %eax 79 jnz no_longmode 80 81/* 82 * Compute the delta between where we were compiled to run at 83 * and where the code will actually run at. 84 * 85 * %ebp contains the address we are loaded at by the boot loader and %ebx 86 * contains the address where we should move the kernel image temporarily 87 * for safe in-place decompression. 88 */ 89 90#ifdef CONFIG_RELOCATABLE 91 movl %ebp, %ebx 92 movl BP_kernel_alignment(%esi), %eax 93 decl %eax 94 addl %eax, %ebx 95 notl %eax 96 andl %eax, %ebx 97#else 98 movl $LOAD_PHYSICAL_ADDR, %ebx 99#endif 100 101 /* Target address to relocate to for decompression */ 102 addl $z_extract_offset, %ebx 103 104/* 105 * Prepare for entering 64 bit mode 106 */ 107 108 /* Load new GDT with the 64bit segments using 32bit descriptor */ 109 leal gdt(%ebp), %eax 110 movl %eax, gdt+2(%ebp) 111 lgdt gdt(%ebp) 112 113 /* Enable PAE mode */ 114 movl $(X86_CR4_PAE), %eax 115 movl %eax, %cr4 116 117 /* 118 * Build early 4G boot pagetable 119 */ 120 /* Initialize Page tables to 0 */ 121 leal pgtable(%ebx), %edi 122 xorl %eax, %eax 123 movl $((4096*6)/4), %ecx 124 rep stosl 125 126 /* Build Level 4 */ 127 leal pgtable + 0(%ebx), %edi 128 leal 0x1007 (%edi), %eax 129 movl %eax, 0(%edi) 130 131 /* Build Level 3 */ 132 leal pgtable + 0x1000(%ebx), %edi 133 leal 0x1007(%edi), %eax 134 movl $4, %ecx 1351: movl %eax, 0x00(%edi) 136 addl $0x00001000, %eax 137 addl $8, %edi 138 decl %ecx 139 jnz 1b 140 141 /* Build Level 2 */ 142 leal pgtable + 0x2000(%ebx), %edi 143 movl $0x00000183, %eax 144 movl $2048, %ecx 1451: movl %eax, 0(%edi) 146 addl $0x00200000, %eax 147 addl $8, %edi 148 decl %ecx 149 jnz 1b 150 151 /* Enable the boot page tables */ 152 leal pgtable(%ebx), %eax 153 movl %eax, %cr3 154 155 /* Enable Long mode in EFER (Extended Feature Enable Register) */ 156 movl $MSR_EFER, %ecx 157 rdmsr 158 btsl $_EFER_LME, %eax 159 wrmsr 160 161 /* After gdt is loaded */ 162 xorl %eax, %eax 163 lldt %ax 164 movl $0x20, %eax 165 ltr %ax 166 167 /* 168 * Setup for the jump to 64bit mode 169 * 170 * When the jump is performend we will be in long mode but 171 * in 32bit compatibility mode with EFER.LME = 1, CS.L = 0, CS.D = 1 172 * (and in turn EFER.LMA = 1). To jump into 64bit mode we use 173 * the new gdt/idt that has __KERNEL_CS with CS.L = 1. 174 * We place all of the values on our mini stack so lret can 175 * used to perform that far jump. 176 */ 177 pushl $__KERNEL_CS 178 leal startup_64(%ebp), %eax 179 pushl %eax 180 181 /* Enter paged protected Mode, activating Long Mode */ 182 movl $(X86_CR0_PG | X86_CR0_PE), %eax /* Enable Paging and Protected mode */ 183 movl %eax, %cr0 184 185 /* Jump from 32bit compatibility mode into 64bit mode. */ 186 lret 187ENDPROC(startup_32) 188 189 .code64 190 .org 0x200 191ENTRY(startup_64) 192 /* 193 * 64bit entry is 0x200 and it is ABI so immutable! 194 * We come here either from startup_32 or directly from a 195 * 64bit bootloader. 196 * If we come here from a bootloader, kernel(text+data+bss+brk), 197 * ramdisk, zero_page, command line could be above 4G. 198 * We depend on an identity mapped page table being provided 199 * that maps our entire kernel(text+data+bss+brk), zero page 200 * and command line. 201 */ 202#ifdef CONFIG_EFI_STUB 203 /* 204 * The entry point for the PE/COFF executable is efi_pe_entry, so 205 * only legacy boot loaders will execute this jmp. 206 */ 207 jmp preferred_addr 208 209ENTRY(efi_pe_entry) 210 mov %rcx, %rdi 211 mov %rdx, %rsi 212 pushq %rdi 213 pushq %rsi 214 call make_boot_params 215 cmpq $0,%rax 216 je 1f 217 mov %rax, %rdx 218 popq %rsi 219 popq %rdi 220 221ENTRY(efi_stub_entry) 222 call efi_main 223 movq %rax,%rsi 224 cmpq $0,%rax 225 jne 2f 2261: 227 /* EFI init failed, so hang. */ 228 hlt 229 jmp 1b 2302: 231 call 3f 2323: 233 popq %rax 234 subq $3b, %rax 235 subq BP_pref_address(%rsi), %rax 236 add BP_code32_start(%esi), %eax 237 leaq preferred_addr(%rax), %rax 238 jmp *%rax 239 240preferred_addr: 241#endif 242 243 /* Setup data segments. */ 244 xorl %eax, %eax 245 movl %eax, %ds 246 movl %eax, %es 247 movl %eax, %ss 248 movl %eax, %fs 249 movl %eax, %gs 250 251 /* 252 * Compute the decompressed kernel start address. It is where 253 * we were loaded at aligned to a 2M boundary. %rbp contains the 254 * decompressed kernel start address. 255 * 256 * If it is a relocatable kernel then decompress and run the kernel 257 * from load address aligned to 2MB addr, otherwise decompress and 258 * run the kernel from LOAD_PHYSICAL_ADDR 259 * 260 * We cannot rely on the calculation done in 32-bit mode, since we 261 * may have been invoked via the 64-bit entry point. 262 */ 263 264 /* Start with the delta to where the kernel will run at. */ 265#ifdef CONFIG_RELOCATABLE 266 leaq startup_32(%rip) /* - $startup_32 */, %rbp 267 movl BP_kernel_alignment(%rsi), %eax 268 decl %eax 269 addq %rax, %rbp 270 notq %rax 271 andq %rax, %rbp 272#else 273 movq $LOAD_PHYSICAL_ADDR, %rbp 274#endif 275 276 /* Target address to relocate to for decompression */ 277 leaq z_extract_offset(%rbp), %rbx 278 279 /* Set up the stack */ 280 leaq boot_stack_end(%rbx), %rsp 281 282 /* Zero EFLAGS */ 283 pushq $0 284 popfq 285 286/* 287 * Copy the compressed kernel to the end of our buffer 288 * where decompression in place becomes safe. 289 */ 290 pushq %rsi 291 leaq (_bss-8)(%rip), %rsi 292 leaq (_bss-8)(%rbx), %rdi 293 movq $_bss /* - $startup_32 */, %rcx 294 shrq $3, %rcx 295 std 296 rep movsq 297 cld 298 popq %rsi 299 300/* 301 * Jump to the relocated address. 302 */ 303 leaq relocated(%rbx), %rax 304 jmp *%rax 305 306 .text 307relocated: 308 309/* 310 * Clear BSS (stack is currently empty) 311 */ 312 xorl %eax, %eax 313 leaq _bss(%rip), %rdi 314 leaq _ebss(%rip), %rcx 315 subq %rdi, %rcx 316 shrq $3, %rcx 317 rep stosq 318 319/* 320 * Adjust our own GOT 321 */ 322 leaq _got(%rip), %rdx 323 leaq _egot(%rip), %rcx 3241: 325 cmpq %rcx, %rdx 326 jae 2f 327 addq %rbx, (%rdx) 328 addq $8, %rdx 329 jmp 1b 3302: 331 332/* 333 * Do the decompression, and jump to the new kernel.. 334 */ 335 pushq %rsi /* Save the real mode argument */ 336 movq %rsi, %rdi /* real mode address */ 337 leaq boot_heap(%rip), %rsi /* malloc area for uncompression */ 338 leaq input_data(%rip), %rdx /* input_data */ 339 movl $z_input_len, %ecx /* input_len */ 340 movq %rbp, %r8 /* output target address */ 341 movq $z_output_len, %r9 /* decompressed length */ 342 call decompress_kernel 343 popq %rsi 344 345/* 346 * Jump to the decompressed kernel. 347 */ 348 jmp *%rbp 349 350 .code32 351no_longmode: 352 /* This isn't an x86-64 CPU so hang */ 3531: 354 hlt 355 jmp 1b 356 357#include "../../kernel/verify_cpu.S" 358 359 .data 360gdt: 361 .word gdt_end - gdt 362 .long gdt 363 .word 0 364 .quad 0x0000000000000000 /* NULL descriptor */ 365 .quad 0x00af9a000000ffff /* __KERNEL_CS */ 366 .quad 0x00cf92000000ffff /* __KERNEL_DS */ 367 .quad 0x0080890000000000 /* TS descriptor */ 368 .quad 0x0000000000000000 /* TS continued */ 369gdt_end: 370 371/* 372 * Stack and heap for uncompression 373 */ 374 .bss 375 .balign 4 376boot_heap: 377 .fill BOOT_HEAP_SIZE, 1, 0 378boot_stack: 379 .fill BOOT_STACK_SIZE, 1, 0 380boot_stack_end: 381 382/* 383 * Space for page tables (not in .bss so not zeroed) 384 */ 385 .section ".pgtable","a",@nobits 386 .balign 4096 387pgtable: 388 .fill 6*4096, 1, 0 389