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#include <asm/bootparam.h> 35 36/* 37 * Locally defined symbols should be marked hidden: 38 */ 39 .hidden _bss 40 .hidden _ebss 41 .hidden _got 42 .hidden _egot 43 44 __HEAD 45 .code32 46ENTRY(startup_32) 47 /* 48 * 32bit entry is 0 and it is ABI so immutable! 49 * If we come here directly from a bootloader, 50 * kernel(text+data+bss+brk) ramdisk, zero_page, command line 51 * all need to be under the 4G limit. 52 */ 53 cld 54 /* 55 * Test KEEP_SEGMENTS flag to see if the bootloader is asking 56 * us to not reload segments 57 */ 58 testb $KEEP_SEGMENTS, BP_loadflags(%esi) 59 jnz 1f 60 61 cli 62 movl $(__BOOT_DS), %eax 63 movl %eax, %ds 64 movl %eax, %es 65 movl %eax, %ss 661: 67 68/* 69 * Calculate the delta between where we were compiled to run 70 * at and where we were actually loaded at. This can only be done 71 * with a short local call on x86. Nothing else will tell us what 72 * address we are running at. The reserved chunk of the real-mode 73 * data at 0x1e4 (defined as a scratch field) are used as the stack 74 * for this calculation. Only 4 bytes are needed. 75 */ 76 leal (BP_scratch+4)(%esi), %esp 77 call 1f 781: popl %ebp 79 subl $1b, %ebp 80 81/* setup a stack and make sure cpu supports long mode. */ 82 movl $boot_stack_end, %eax 83 addl %ebp, %eax 84 movl %eax, %esp 85 86 call verify_cpu 87 testl %eax, %eax 88 jnz no_longmode 89 90/* 91 * Compute the delta between where we were compiled to run at 92 * and where the code will actually run at. 93 * 94 * %ebp contains the address we are loaded at by the boot loader and %ebx 95 * contains the address where we should move the kernel image temporarily 96 * for safe in-place decompression. 97 */ 98 99#ifdef CONFIG_RELOCATABLE 100 movl %ebp, %ebx 101 movl BP_kernel_alignment(%esi), %eax 102 decl %eax 103 addl %eax, %ebx 104 notl %eax 105 andl %eax, %ebx 106 cmpl $LOAD_PHYSICAL_ADDR, %ebx 107 jge 1f 108#endif 109 movl $LOAD_PHYSICAL_ADDR, %ebx 1101: 111 112 /* Target address to relocate to for decompression */ 113 movl BP_init_size(%esi), %eax 114 subl $_end, %eax 115 addl %eax, %ebx 116 117/* 118 * Prepare for entering 64 bit mode 119 */ 120 121 /* Load new GDT with the 64bit segments using 32bit descriptor */ 122 addl %ebp, gdt+2(%ebp) 123 lgdt gdt(%ebp) 124 125 /* Enable PAE mode */ 126 movl %cr4, %eax 127 orl $X86_CR4_PAE, %eax 128 movl %eax, %cr4 129 130 /* 131 * Build early 4G boot pagetable 132 */ 133 /* Initialize Page tables to 0 */ 134 leal pgtable(%ebx), %edi 135 xorl %eax, %eax 136 movl $(BOOT_INIT_PGT_SIZE/4), %ecx 137 rep stosl 138 139 /* Build Level 4 */ 140 leal pgtable + 0(%ebx), %edi 141 leal 0x1007 (%edi), %eax 142 movl %eax, 0(%edi) 143 144 /* Build Level 3 */ 145 leal pgtable + 0x1000(%ebx), %edi 146 leal 0x1007(%edi), %eax 147 movl $4, %ecx 1481: movl %eax, 0x00(%edi) 149 addl $0x00001000, %eax 150 addl $8, %edi 151 decl %ecx 152 jnz 1b 153 154 /* Build Level 2 */ 155 leal pgtable + 0x2000(%ebx), %edi 156 movl $0x00000183, %eax 157 movl $2048, %ecx 1581: movl %eax, 0(%edi) 159 addl $0x00200000, %eax 160 addl $8, %edi 161 decl %ecx 162 jnz 1b 163 164 /* Enable the boot page tables */ 165 leal pgtable(%ebx), %eax 166 movl %eax, %cr3 167 168 /* Enable Long mode in EFER (Extended Feature Enable Register) */ 169 movl $MSR_EFER, %ecx 170 rdmsr 171 btsl $_EFER_LME, %eax 172 wrmsr 173 174 /* After gdt is loaded */ 175 xorl %eax, %eax 176 lldt %ax 177 movl $__BOOT_TSS, %eax 178 ltr %ax 179 180 /* 181 * Setup for the jump to 64bit mode 182 * 183 * When the jump is performend we will be in long mode but 184 * in 32bit compatibility mode with EFER.LME = 1, CS.L = 0, CS.D = 1 185 * (and in turn EFER.LMA = 1). To jump into 64bit mode we use 186 * the new gdt/idt that has __KERNEL_CS with CS.L = 1. 187 * We place all of the values on our mini stack so lret can 188 * used to perform that far jump. 189 */ 190 pushl $__KERNEL_CS 191 leal startup_64(%ebp), %eax 192#ifdef CONFIG_EFI_MIXED 193 movl efi32_config(%ebp), %ebx 194 cmp $0, %ebx 195 jz 1f 196 leal handover_entry(%ebp), %eax 1971: 198#endif 199 pushl %eax 200 201 /* Enter paged protected Mode, activating Long Mode */ 202 movl $(X86_CR0_PG | X86_CR0_PE), %eax /* Enable Paging and Protected mode */ 203 movl %eax, %cr0 204 205 /* Jump from 32bit compatibility mode into 64bit mode. */ 206 lret 207ENDPROC(startup_32) 208 209#ifdef CONFIG_EFI_MIXED 210 .org 0x190 211ENTRY(efi32_stub_entry) 212 add $0x4, %esp /* Discard return address */ 213 popl %ecx 214 popl %edx 215 popl %esi 216 217 leal (BP_scratch+4)(%esi), %esp 218 call 1f 2191: pop %ebp 220 subl $1b, %ebp 221 222 movl %ecx, efi32_config(%ebp) 223 movl %edx, efi32_config+8(%ebp) 224 sgdtl efi32_boot_gdt(%ebp) 225 226 leal efi32_config(%ebp), %eax 227 movl %eax, efi_config(%ebp) 228 229 jmp startup_32 230ENDPROC(efi32_stub_entry) 231#endif 232 233 .code64 234 .org 0x200 235ENTRY(startup_64) 236 /* 237 * 64bit entry is 0x200 and it is ABI so immutable! 238 * We come here either from startup_32 or directly from a 239 * 64bit bootloader. 240 * If we come here from a bootloader, kernel(text+data+bss+brk), 241 * ramdisk, zero_page, command line could be above 4G. 242 * We depend on an identity mapped page table being provided 243 * that maps our entire kernel(text+data+bss+brk), zero page 244 * and command line. 245 */ 246#ifdef CONFIG_EFI_STUB 247 /* 248 * The entry point for the PE/COFF executable is efi_pe_entry, so 249 * only legacy boot loaders will execute this jmp. 250 */ 251 jmp preferred_addr 252 253ENTRY(efi_pe_entry) 254 movq %rcx, efi64_config(%rip) /* Handle */ 255 movq %rdx, efi64_config+8(%rip) /* EFI System table pointer */ 256 257 leaq efi64_config(%rip), %rax 258 movq %rax, efi_config(%rip) 259 260 call 1f 2611: popq %rbp 262 subq $1b, %rbp 263 264 /* 265 * Relocate efi_config->call(). 266 */ 267 addq %rbp, efi64_config+40(%rip) 268 269 movq %rax, %rdi 270 call make_boot_params 271 cmpq $0,%rax 272 je fail 273 mov %rax, %rsi 274 leaq startup_32(%rip), %rax 275 movl %eax, BP_code32_start(%rsi) 276 jmp 2f /* Skip the relocation */ 277 278handover_entry: 279 call 1f 2801: popq %rbp 281 subq $1b, %rbp 282 283 /* 284 * Relocate efi_config->call(). 285 */ 286 movq efi_config(%rip), %rax 287 addq %rbp, 40(%rax) 2882: 289 movq efi_config(%rip), %rdi 290 call efi_main 291 movq %rax,%rsi 292 cmpq $0,%rax 293 jne 2f 294fail: 295 /* EFI init failed, so hang. */ 296 hlt 297 jmp fail 2982: 299 movl BP_code32_start(%esi), %eax 300 leaq preferred_addr(%rax), %rax 301 jmp *%rax 302 303preferred_addr: 304#endif 305 306 /* Setup data segments. */ 307 xorl %eax, %eax 308 movl %eax, %ds 309 movl %eax, %es 310 movl %eax, %ss 311 movl %eax, %fs 312 movl %eax, %gs 313 314 /* 315 * Compute the decompressed kernel start address. It is where 316 * we were loaded at aligned to a 2M boundary. %rbp contains the 317 * decompressed kernel start address. 318 * 319 * If it is a relocatable kernel then decompress and run the kernel 320 * from load address aligned to 2MB addr, otherwise decompress and 321 * run the kernel from LOAD_PHYSICAL_ADDR 322 * 323 * We cannot rely on the calculation done in 32-bit mode, since we 324 * may have been invoked via the 64-bit entry point. 325 */ 326 327 /* Start with the delta to where the kernel will run at. */ 328#ifdef CONFIG_RELOCATABLE 329 leaq startup_32(%rip) /* - $startup_32 */, %rbp 330 movl BP_kernel_alignment(%rsi), %eax 331 decl %eax 332 addq %rax, %rbp 333 notq %rax 334 andq %rax, %rbp 335 cmpq $LOAD_PHYSICAL_ADDR, %rbp 336 jge 1f 337#endif 338 movq $LOAD_PHYSICAL_ADDR, %rbp 3391: 340 341 /* Target address to relocate to for decompression */ 342 movl BP_init_size(%rsi), %ebx 343 subl $_end, %ebx 344 addq %rbp, %rbx 345 346 /* Set up the stack */ 347 leaq boot_stack_end(%rbx), %rsp 348 349#ifdef CONFIG_X86_5LEVEL 350 /* Check if 5-level paging has already enabled */ 351 movq %cr4, %rax 352 testl $X86_CR4_LA57, %eax 353 jnz lvl5 354 355 /* 356 * At this point we are in long mode with 4-level paging enabled, 357 * but we want to enable 5-level paging. 358 * 359 * The problem is that we cannot do it directly. Setting LA57 in 360 * long mode would trigger #GP. So we need to switch off long mode 361 * first. 362 * 363 * NOTE: This is not going to work if bootloader put us above 4G 364 * limit. 365 * 366 * The first step is go into compatibility mode. 367 */ 368 369 /* Clear additional page table */ 370 leaq lvl5_pgtable(%rbx), %rdi 371 xorq %rax, %rax 372 movq $(PAGE_SIZE/8), %rcx 373 rep stosq 374 375 /* 376 * Setup current CR3 as the first and only entry in a new top level 377 * page table. 378 */ 379 movq %cr3, %rdi 380 leaq 0x7 (%rdi), %rax 381 movq %rax, lvl5_pgtable(%rbx) 382 383 /* Switch to compatibility mode (CS.L = 0 CS.D = 1) via far return */ 384 pushq $__KERNEL32_CS 385 leaq compatible_mode(%rip), %rax 386 pushq %rax 387 lretq 388lvl5: 389#endif 390 391 /* Zero EFLAGS */ 392 pushq $0 393 popfq 394 395/* 396 * Copy the compressed kernel to the end of our buffer 397 * where decompression in place becomes safe. 398 */ 399 pushq %rsi 400 leaq (_bss-8)(%rip), %rsi 401 leaq (_bss-8)(%rbx), %rdi 402 movq $_bss /* - $startup_32 */, %rcx 403 shrq $3, %rcx 404 std 405 rep movsq 406 cld 407 popq %rsi 408 409/* 410 * Jump to the relocated address. 411 */ 412 leaq relocated(%rbx), %rax 413 jmp *%rax 414 415#ifdef CONFIG_EFI_STUB 416 .org 0x390 417ENTRY(efi64_stub_entry) 418 movq %rdi, efi64_config(%rip) /* Handle */ 419 movq %rsi, efi64_config+8(%rip) /* EFI System table pointer */ 420 421 leaq efi64_config(%rip), %rax 422 movq %rax, efi_config(%rip) 423 424 movq %rdx, %rsi 425 jmp handover_entry 426ENDPROC(efi64_stub_entry) 427#endif 428 429 .text 430relocated: 431 432/* 433 * Clear BSS (stack is currently empty) 434 */ 435 xorl %eax, %eax 436 leaq _bss(%rip), %rdi 437 leaq _ebss(%rip), %rcx 438 subq %rdi, %rcx 439 shrq $3, %rcx 440 rep stosq 441 442/* 443 * Adjust our own GOT 444 */ 445 leaq _got(%rip), %rdx 446 leaq _egot(%rip), %rcx 4471: 448 cmpq %rcx, %rdx 449 jae 2f 450 addq %rbx, (%rdx) 451 addq $8, %rdx 452 jmp 1b 4532: 454 455/* 456 * Do the extraction, and jump to the new kernel.. 457 */ 458 pushq %rsi /* Save the real mode argument */ 459 movq %rsi, %rdi /* real mode address */ 460 leaq boot_heap(%rip), %rsi /* malloc area for uncompression */ 461 leaq input_data(%rip), %rdx /* input_data */ 462 movl $z_input_len, %ecx /* input_len */ 463 movq %rbp, %r8 /* output target address */ 464 movq $z_output_len, %r9 /* decompressed length, end of relocs */ 465 call extract_kernel /* returns kernel location in %rax */ 466 popq %rsi 467 468/* 469 * Jump to the decompressed kernel. 470 */ 471 jmp *%rax 472 473 .code32 474#ifdef CONFIG_X86_5LEVEL 475compatible_mode: 476 /* Setup data and stack segments */ 477 movl $__KERNEL_DS, %eax 478 movl %eax, %ds 479 movl %eax, %ss 480 481 /* Disable paging */ 482 movl %cr0, %eax 483 btrl $X86_CR0_PG_BIT, %eax 484 movl %eax, %cr0 485 486 /* Point CR3 to 5-level paging */ 487 leal lvl5_pgtable(%ebx), %eax 488 movl %eax, %cr3 489 490 /* Enable PAE and LA57 mode */ 491 movl %cr4, %eax 492 orl $(X86_CR4_PAE | X86_CR4_LA57), %eax 493 movl %eax, %cr4 494 495 /* Calculate address we are running at */ 496 call 1f 4971: popl %edi 498 subl $1b, %edi 499 500 /* Prepare stack for far return to Long Mode */ 501 pushl $__KERNEL_CS 502 leal lvl5(%edi), %eax 503 push %eax 504 505 /* Enable paging back */ 506 movl $(X86_CR0_PG | X86_CR0_PE), %eax 507 movl %eax, %cr0 508 509 lret 510#endif 511 512no_longmode: 513 /* This isn't an x86-64 CPU so hang */ 5141: 515 hlt 516 jmp 1b 517 518#include "../../kernel/verify_cpu.S" 519 520 .data 521gdt: 522 .word gdt_end - gdt 523 .long gdt 524 .word 0 525 .quad 0x00cf9a000000ffff /* __KERNEL32_CS */ 526 .quad 0x00af9a000000ffff /* __KERNEL_CS */ 527 .quad 0x00cf92000000ffff /* __KERNEL_DS */ 528 .quad 0x0080890000000000 /* TS descriptor */ 529 .quad 0x0000000000000000 /* TS continued */ 530gdt_end: 531 532#ifdef CONFIG_EFI_STUB 533efi_config: 534 .quad 0 535 536#ifdef CONFIG_EFI_MIXED 537 .global efi32_config 538efi32_config: 539 .fill 5,8,0 540 .quad efi64_thunk 541 .byte 0 542#endif 543 544 .global efi64_config 545efi64_config: 546 .fill 5,8,0 547 .quad efi_call 548 .byte 1 549#endif /* CONFIG_EFI_STUB */ 550 551/* 552 * Stack and heap for uncompression 553 */ 554 .bss 555 .balign 4 556boot_heap: 557 .fill BOOT_HEAP_SIZE, 1, 0 558boot_stack: 559 .fill BOOT_STACK_SIZE, 1, 0 560boot_stack_end: 561 562/* 563 * Space for page tables (not in .bss so not zeroed) 564 */ 565 .section ".pgtable","a",@nobits 566 .balign 4096 567pgtable: 568 .fill BOOT_PGT_SIZE, 1, 0 569#ifdef CONFIG_X86_5LEVEL 570lvl5_pgtable: 571 .fill PAGE_SIZE, 1, 0 572#endif 573