1/* 2 * 3 * Copyright (C) 1991, 1992 Linus Torvalds 4 * 5 * Enhanced CPU detection and feature setting code by Mike Jagdis 6 * and Martin Mares, November 1997. 7 */ 8 9.text 10#include <linux/threads.h> 11#include <linux/init.h> 12#include <linux/linkage.h> 13#include <asm/segment.h> 14#include <asm/page.h> 15#include <asm/pgtable.h> 16#include <asm/desc.h> 17#include <asm/cache.h> 18#include <asm/thread_info.h> 19#include <asm/asm-offsets.h> 20#include <asm/setup.h> 21#include <asm/processor-flags.h> 22 23/* Physical address */ 24#define pa(X) ((X) - __PAGE_OFFSET) 25 26/* 27 * References to members of the new_cpu_data structure. 28 */ 29 30#define X86 new_cpu_data+CPUINFO_x86 31#define X86_VENDOR new_cpu_data+CPUINFO_x86_vendor 32#define X86_MODEL new_cpu_data+CPUINFO_x86_model 33#define X86_MASK new_cpu_data+CPUINFO_x86_mask 34#define X86_HARD_MATH new_cpu_data+CPUINFO_hard_math 35#define X86_CPUID new_cpu_data+CPUINFO_cpuid_level 36#define X86_CAPABILITY new_cpu_data+CPUINFO_x86_capability 37#define X86_VENDOR_ID new_cpu_data+CPUINFO_x86_vendor_id 38 39/* 40 * This is how much memory *in addition to the memory covered up to 41 * and including _end* we need mapped initially. 42 * We need: 43 * - one bit for each possible page, but only in low memory, which means 44 * 2^32/4096/8 = 128K worst case (4G/4G split.) 45 * - enough space to map all low memory, which means 46 * (2^32/4096) / 1024 pages (worst case, non PAE) 47 * (2^32/4096) / 512 + 4 pages (worst case for PAE) 48 * - a few pages for allocator use before the kernel pagetable has 49 * been set up 50 * 51 * Modulo rounding, each megabyte assigned here requires a kilobyte of 52 * memory, which is currently unreclaimed. 53 * 54 * This should be a multiple of a page. 55 */ 56LOW_PAGES = 1<<(32-PAGE_SHIFT_asm) 57 58/* 59 * To preserve the DMA pool in PAGEALLOC kernels, we'll allocate 60 * pagetables from above the 16MB DMA limit, so we'll have to set 61 * up pagetables 16MB more (worst-case): 62 */ 63#ifdef CONFIG_DEBUG_PAGEALLOC 64LOW_PAGES = LOW_PAGES + 0x1000000 65#endif 66 67#if PTRS_PER_PMD > 1 68PAGE_TABLE_SIZE = (LOW_PAGES / PTRS_PER_PMD) + PTRS_PER_PGD 69#else 70PAGE_TABLE_SIZE = (LOW_PAGES / PTRS_PER_PGD) 71#endif 72BOOTBITMAP_SIZE = LOW_PAGES / 8 73ALLOCATOR_SLOP = 4 74 75INIT_MAP_BEYOND_END = BOOTBITMAP_SIZE + (PAGE_TABLE_SIZE + ALLOCATOR_SLOP)*PAGE_SIZE_asm 76 77/* 78 * 32-bit kernel entrypoint; only used by the boot CPU. On entry, 79 * %esi points to the real-mode code as a 32-bit pointer. 80 * CS and DS must be 4 GB flat segments, but we don't depend on 81 * any particular GDT layout, because we load our own as soon as we 82 * can. 83 */ 84.section .text.head,"ax",@progbits 85ENTRY(startup_32) 86 /* test KEEP_SEGMENTS flag to see if the bootloader is asking 87 us to not reload segments */ 88 testb $(1<<6), BP_loadflags(%esi) 89 jnz 2f 90 91/* 92 * Set segments to known values. 93 */ 94 lgdt pa(boot_gdt_descr) 95 movl $(__BOOT_DS),%eax 96 movl %eax,%ds 97 movl %eax,%es 98 movl %eax,%fs 99 movl %eax,%gs 1002: 101 102/* 103 * Clear BSS first so that there are no surprises... 104 */ 105 cld 106 xorl %eax,%eax 107 movl $pa(__bss_start),%edi 108 movl $pa(__bss_stop),%ecx 109 subl %edi,%ecx 110 shrl $2,%ecx 111 rep ; stosl 112/* 113 * Copy bootup parameters out of the way. 114 * Note: %esi still has the pointer to the real-mode data. 115 * With the kexec as boot loader, parameter segment might be loaded beyond 116 * kernel image and might not even be addressable by early boot page tables. 117 * (kexec on panic case). Hence copy out the parameters before initializing 118 * page tables. 119 */ 120 movl $pa(boot_params),%edi 121 movl $(PARAM_SIZE/4),%ecx 122 cld 123 rep 124 movsl 125 movl pa(boot_params) + NEW_CL_POINTER,%esi 126 andl %esi,%esi 127 jz 1f # No comand line 128 movl $pa(boot_command_line),%edi 129 movl $(COMMAND_LINE_SIZE/4),%ecx 130 rep 131 movsl 1321: 133 134#ifdef CONFIG_PARAVIRT 135 /* This is can only trip for a broken bootloader... */ 136 cmpw $0x207, pa(boot_params + BP_version) 137 jb default_entry 138 139 /* Paravirt-compatible boot parameters. Look to see what architecture 140 we're booting under. */ 141 movl pa(boot_params + BP_hardware_subarch), %eax 142 cmpl $num_subarch_entries, %eax 143 jae bad_subarch 144 145 movl pa(subarch_entries)(,%eax,4), %eax 146 subl $__PAGE_OFFSET, %eax 147 jmp *%eax 148 149bad_subarch: 150WEAK(lguest_entry) 151WEAK(xen_entry) 152 /* Unknown implementation; there's really 153 nothing we can do at this point. */ 154 ud2a 155 156 __INITDATA 157 158subarch_entries: 159 .long default_entry /* normal x86/PC */ 160 .long lguest_entry /* lguest hypervisor */ 161 .long xen_entry /* Xen hypervisor */ 162num_subarch_entries = (. - subarch_entries) / 4 163.previous 164#endif /* CONFIG_PARAVIRT */ 165 166/* 167 * Initialize page tables. This creates a PDE and a set of page 168 * tables, which are located immediately beyond _end. The variable 169 * init_pg_tables_end is set up to point to the first "safe" location. 170 * Mappings are created both at virtual address 0 (identity mapping) 171 * and PAGE_OFFSET for up to _end+sizeof(page tables)+INIT_MAP_BEYOND_END. 172 * 173 * Note that the stack is not yet set up! 174 */ 175#define PTE_ATTR 0x007 /* PRESENT+RW+USER */ 176#define PDE_ATTR 0x067 /* PRESENT+RW+USER+DIRTY+ACCESSED */ 177#define PGD_ATTR 0x001 /* PRESENT (no other attributes) */ 178 179default_entry: 180#ifdef CONFIG_X86_PAE 181 182 /* 183 * In PAE mode swapper_pg_dir is statically defined to contain enough 184 * entries to cover the VMSPLIT option (that is the top 1, 2 or 3 185 * entries). The identity mapping is handled by pointing two PGD 186 * entries to the first kernel PMD. 187 * 188 * Note the upper half of each PMD or PTE are always zero at 189 * this stage. 190 */ 191 192#define KPMDS (((-__PAGE_OFFSET) >> 30) & 3) /* Number of kernel PMDs */ 193 194 xorl %ebx,%ebx /* %ebx is kept at zero */ 195 196 movl $pa(pg0), %edi 197 movl %edi, pa(init_pg_tables_start) 198 movl $pa(swapper_pg_pmd), %edx 199 movl $PTE_ATTR, %eax 20010: 201 leal PDE_ATTR(%edi),%ecx /* Create PMD entry */ 202 movl %ecx,(%edx) /* Store PMD entry */ 203 /* Upper half already zero */ 204 addl $8,%edx 205 movl $512,%ecx 20611: 207 stosl 208 xchgl %eax,%ebx 209 stosl 210 xchgl %eax,%ebx 211 addl $0x1000,%eax 212 loop 11b 213 214 /* 215 * End condition: we must map up to and including INIT_MAP_BEYOND_END 216 * bytes beyond the end of our own page tables. 217 */ 218 leal (INIT_MAP_BEYOND_END+PTE_ATTR)(%edi),%ebp 219 cmpl %ebp,%eax 220 jb 10b 2211: 222 movl %edi,pa(init_pg_tables_end) 223 shrl $12, %eax 224 movl %eax, pa(max_pfn_mapped) 225 226 /* Do early initialization of the fixmap area */ 227 movl $pa(swapper_pg_fixmap)+PDE_ATTR,%eax 228 movl %eax,pa(swapper_pg_pmd+0x1000*KPMDS-8) 229#else /* Not PAE */ 230 231page_pde_offset = (__PAGE_OFFSET >> 20); 232 233 movl $pa(pg0), %edi 234 movl %edi, pa(init_pg_tables_start) 235 movl $pa(swapper_pg_dir), %edx 236 movl $PTE_ATTR, %eax 23710: 238 leal PDE_ATTR(%edi),%ecx /* Create PDE entry */ 239 movl %ecx,(%edx) /* Store identity PDE entry */ 240 movl %ecx,page_pde_offset(%edx) /* Store kernel PDE entry */ 241 addl $4,%edx 242 movl $1024, %ecx 24311: 244 stosl 245 addl $0x1000,%eax 246 loop 11b 247 /* 248 * End condition: we must map up to and including INIT_MAP_BEYOND_END 249 * bytes beyond the end of our own page tables; the +0x007 is 250 * the attribute bits 251 */ 252 leal (INIT_MAP_BEYOND_END+PTE_ATTR)(%edi),%ebp 253 cmpl %ebp,%eax 254 jb 10b 255 movl %edi,pa(init_pg_tables_end) 256 shrl $12, %eax 257 movl %eax, pa(max_pfn_mapped) 258 259 /* Do early initialization of the fixmap area */ 260 movl $pa(swapper_pg_fixmap)+PDE_ATTR,%eax 261 movl %eax,pa(swapper_pg_dir+0xffc) 262#endif 263 jmp 3f 264/* 265 * Non-boot CPU entry point; entered from trampoline.S 266 * We can't lgdt here, because lgdt itself uses a data segment, but 267 * we know the trampoline has already loaded the boot_gdt for us. 268 * 269 * If cpu hotplug is not supported then this code can go in init section 270 * which will be freed later 271 */ 272 273#ifndef CONFIG_HOTPLUG_CPU 274.section .init.text,"ax",@progbits 275#endif 276 277#ifdef CONFIG_SMP 278ENTRY(startup_32_smp) 279 cld 280 movl $(__BOOT_DS),%eax 281 movl %eax,%ds 282 movl %eax,%es 283 movl %eax,%fs 284 movl %eax,%gs 285#endif /* CONFIG_SMP */ 2863: 287 288/* 289 * New page tables may be in 4Mbyte page mode and may 290 * be using the global pages. 291 * 292 * NOTE! If we are on a 486 we may have no cr4 at all! 293 * So we do not try to touch it unless we really have 294 * some bits in it to set. This won't work if the BSP 295 * implements cr4 but this AP does not -- very unlikely 296 * but be warned! The same applies to the pse feature 297 * if not equally supported. --macro 298 * 299 * NOTE! We have to correct for the fact that we're 300 * not yet offset PAGE_OFFSET.. 301 */ 302#define cr4_bits pa(mmu_cr4_features) 303 movl cr4_bits,%edx 304 andl %edx,%edx 305 jz 6f 306 movl %cr4,%eax # Turn on paging options (PSE,PAE,..) 307 orl %edx,%eax 308 movl %eax,%cr4 309 310 btl $5, %eax # check if PAE is enabled 311 jnc 6f 312 313 /* Check if extended functions are implemented */ 314 movl $0x80000000, %eax 315 cpuid 316 cmpl $0x80000000, %eax 317 jbe 6f 318 mov $0x80000001, %eax 319 cpuid 320 /* Execute Disable bit supported? */ 321 btl $20, %edx 322 jnc 6f 323 324 /* Setup EFER (Extended Feature Enable Register) */ 325 movl $0xc0000080, %ecx 326 rdmsr 327 328 btsl $11, %eax 329 /* Make changes effective */ 330 wrmsr 331 3326: 333 334/* 335 * Enable paging 336 */ 337 movl $pa(swapper_pg_dir),%eax 338 movl %eax,%cr3 /* set the page table pointer.. */ 339 movl %cr0,%eax 340 orl $X86_CR0_PG,%eax 341 movl %eax,%cr0 /* ..and set paging (PG) bit */ 342 ljmp $__BOOT_CS,$1f /* Clear prefetch and normalize %eip */ 3431: 344 /* Set up the stack pointer */ 345 lss stack_start,%esp 346 347/* 348 * Initialize eflags. Some BIOS's leave bits like NT set. This would 349 * confuse the debugger if this code is traced. 350 * XXX - best to initialize before switching to protected mode. 351 */ 352 pushl $0 353 popfl 354 355#ifdef CONFIG_SMP 356 cmpb $0, ready 357 jz 1f /* Initial CPU cleans BSS */ 358 jmp checkCPUtype 3591: 360#endif /* CONFIG_SMP */ 361 362/* 363 * start system 32-bit setup. We need to re-do some of the things done 364 * in 16-bit mode for the "real" operations. 365 */ 366 call setup_idt 367 368checkCPUtype: 369 370 movl $-1,X86_CPUID # -1 for no CPUID initially 371 372/* check if it is 486 or 386. */ 373/* 374 * XXX - this does a lot of unnecessary setup. Alignment checks don't 375 * apply at our cpl of 0 and the stack ought to be aligned already, and 376 * we don't need to preserve eflags. 377 */ 378 379 movb $3,X86 # at least 386 380 pushfl # push EFLAGS 381 popl %eax # get EFLAGS 382 movl %eax,%ecx # save original EFLAGS 383 xorl $0x240000,%eax # flip AC and ID bits in EFLAGS 384 pushl %eax # copy to EFLAGS 385 popfl # set EFLAGS 386 pushfl # get new EFLAGS 387 popl %eax # put it in eax 388 xorl %ecx,%eax # change in flags 389 pushl %ecx # restore original EFLAGS 390 popfl 391 testl $0x40000,%eax # check if AC bit changed 392 je is386 393 394 movb $4,X86 # at least 486 395 testl $0x200000,%eax # check if ID bit changed 396 je is486 397 398 /* get vendor info */ 399 xorl %eax,%eax # call CPUID with 0 -> return vendor ID 400 cpuid 401 movl %eax,X86_CPUID # save CPUID level 402 movl %ebx,X86_VENDOR_ID # lo 4 chars 403 movl %edx,X86_VENDOR_ID+4 # next 4 chars 404 movl %ecx,X86_VENDOR_ID+8 # last 4 chars 405 406 orl %eax,%eax # do we have processor info as well? 407 je is486 408 409 movl $1,%eax # Use the CPUID instruction to get CPU type 410 cpuid 411 movb %al,%cl # save reg for future use 412 andb $0x0f,%ah # mask processor family 413 movb %ah,X86 414 andb $0xf0,%al # mask model 415 shrb $4,%al 416 movb %al,X86_MODEL 417 andb $0x0f,%cl # mask mask revision 418 movb %cl,X86_MASK 419 movl %edx,X86_CAPABILITY 420 421is486: movl $0x50022,%ecx # set AM, WP, NE and MP 422 jmp 2f 423 424is386: movl $2,%ecx # set MP 4252: movl %cr0,%eax 426 andl $0x80000011,%eax # Save PG,PE,ET 427 orl %ecx,%eax 428 movl %eax,%cr0 429 430 call check_x87 431 lgdt early_gdt_descr 432 lidt idt_descr 433 ljmp $(__KERNEL_CS),$1f 4341: movl $(__KERNEL_DS),%eax # reload all the segment registers 435 movl %eax,%ss # after changing gdt. 436 movl %eax,%fs # gets reset once there's real percpu 437 438 movl $(__USER_DS),%eax # DS/ES contains default USER segment 439 movl %eax,%ds 440 movl %eax,%es 441 442 xorl %eax,%eax # Clear GS and LDT 443 movl %eax,%gs 444 lldt %ax 445 446 cld # gcc2 wants the direction flag cleared at all times 447 pushl $0 # fake return address for unwinder 448#ifdef CONFIG_SMP 449 movb ready, %cl 450 movb $1, ready 451 cmpb $0,%cl # the first CPU calls start_kernel 452 je 1f 453 movl $(__KERNEL_PERCPU), %eax 454 movl %eax,%fs # set this cpu's percpu 455 movl (stack_start), %esp 4561: 457#endif /* CONFIG_SMP */ 458 jmp *(initial_code) 459.align 4 460ENTRY(initial_code) 461 .long i386_start_kernel 462 463/* 464 * We depend on ET to be correct. This checks for 287/387. 465 */ 466check_x87: 467 movb $0,X86_HARD_MATH 468 clts 469 fninit 470 fstsw %ax 471 cmpb $0,%al 472 je 1f 473 movl %cr0,%eax /* no coprocessor: have to set bits */ 474 xorl $4,%eax /* set EM */ 475 movl %eax,%cr0 476 ret 477 ALIGN 4781: movb $1,X86_HARD_MATH 479 .byte 0xDB,0xE4 /* fsetpm for 287, ignored by 387 */ 480 ret 481 482/* 483 * setup_idt 484 * 485 * sets up a idt with 256 entries pointing to 486 * ignore_int, interrupt gates. It doesn't actually load 487 * idt - that can be done only after paging has been enabled 488 * and the kernel moved to PAGE_OFFSET. Interrupts 489 * are enabled elsewhere, when we can be relatively 490 * sure everything is ok. 491 * 492 * Warning: %esi is live across this function. 493 */ 494setup_idt: 495 lea ignore_int,%edx 496 movl $(__KERNEL_CS << 16),%eax 497 movw %dx,%ax /* selector = 0x0010 = cs */ 498 movw $0x8E00,%dx /* interrupt gate - dpl=0, present */ 499 500 lea idt_table,%edi 501 mov $256,%ecx 502rp_sidt: 503 movl %eax,(%edi) 504 movl %edx,4(%edi) 505 addl $8,%edi 506 dec %ecx 507 jne rp_sidt 508 509.macro set_early_handler handler,trapno 510 lea \handler,%edx 511 movl $(__KERNEL_CS << 16),%eax 512 movw %dx,%ax 513 movw $0x8E00,%dx /* interrupt gate - dpl=0, present */ 514 lea idt_table,%edi 515 movl %eax,8*\trapno(%edi) 516 movl %edx,8*\trapno+4(%edi) 517.endm 518 519 set_early_handler handler=early_divide_err,trapno=0 520 set_early_handler handler=early_illegal_opcode,trapno=6 521 set_early_handler handler=early_protection_fault,trapno=13 522 set_early_handler handler=early_page_fault,trapno=14 523 524 ret 525 526early_divide_err: 527 xor %edx,%edx 528 pushl $0 /* fake errcode */ 529 jmp early_fault 530 531early_illegal_opcode: 532 movl $6,%edx 533 pushl $0 /* fake errcode */ 534 jmp early_fault 535 536early_protection_fault: 537 movl $13,%edx 538 jmp early_fault 539 540early_page_fault: 541 movl $14,%edx 542 jmp early_fault 543 544early_fault: 545 cld 546#ifdef CONFIG_PRINTK 547 pusha 548 movl $(__KERNEL_DS),%eax 549 movl %eax,%ds 550 movl %eax,%es 551 cmpl $2,early_recursion_flag 552 je hlt_loop 553 incl early_recursion_flag 554 movl %cr2,%eax 555 pushl %eax 556 pushl %edx /* trapno */ 557 pushl $fault_msg 558#ifdef CONFIG_EARLY_PRINTK 559 call early_printk 560#else 561 call printk 562#endif 563#endif 564 call dump_stack 565hlt_loop: 566 hlt 567 jmp hlt_loop 568 569/* This is the default interrupt "handler" :-) */ 570 ALIGN 571ignore_int: 572 cld 573#ifdef CONFIG_PRINTK 574 pushl %eax 575 pushl %ecx 576 pushl %edx 577 pushl %es 578 pushl %ds 579 movl $(__KERNEL_DS),%eax 580 movl %eax,%ds 581 movl %eax,%es 582 cmpl $2,early_recursion_flag 583 je hlt_loop 584 incl early_recursion_flag 585 pushl 16(%esp) 586 pushl 24(%esp) 587 pushl 32(%esp) 588 pushl 40(%esp) 589 pushl $int_msg 590#ifdef CONFIG_EARLY_PRINTK 591 call early_printk 592#else 593 call printk 594#endif 595 addl $(5*4),%esp 596 popl %ds 597 popl %es 598 popl %edx 599 popl %ecx 600 popl %eax 601#endif 602 iret 603 604.section .text 605/* 606 * Real beginning of normal "text" segment 607 */ 608ENTRY(stext) 609ENTRY(_stext) 610 611/* 612 * BSS section 613 */ 614.section ".bss.page_aligned","wa" 615 .align PAGE_SIZE_asm 616#ifdef CONFIG_X86_PAE 617swapper_pg_pmd: 618 .fill 1024*KPMDS,4,0 619#else 620ENTRY(swapper_pg_dir) 621 .fill 1024,4,0 622#endif 623swapper_pg_fixmap: 624 .fill 1024,4,0 625ENTRY(empty_zero_page) 626 .fill 4096,1,0 627/* 628 * This starts the data section. 629 */ 630#ifdef CONFIG_X86_PAE 631.section ".data.page_aligned","wa" 632 /* Page-aligned for the benefit of paravirt? */ 633 .align PAGE_SIZE_asm 634ENTRY(swapper_pg_dir) 635 .long pa(swapper_pg_pmd+PGD_ATTR),0 /* low identity map */ 636# if KPMDS == 3 637 .long pa(swapper_pg_pmd+PGD_ATTR),0 638 .long pa(swapper_pg_pmd+PGD_ATTR+0x1000),0 639 .long pa(swapper_pg_pmd+PGD_ATTR+0x2000),0 640# elif KPMDS == 2 641 .long 0,0 642 .long pa(swapper_pg_pmd+PGD_ATTR),0 643 .long pa(swapper_pg_pmd+PGD_ATTR+0x1000),0 644# elif KPMDS == 1 645 .long 0,0 646 .long 0,0 647 .long pa(swapper_pg_pmd+PGD_ATTR),0 648# else 649# error "Kernel PMDs should be 1, 2 or 3" 650# endif 651 .align PAGE_SIZE_asm /* needs to be page-sized too */ 652#endif 653 654.data 655ENTRY(stack_start) 656 .long init_thread_union+THREAD_SIZE 657 .long __BOOT_DS 658 659ready: .byte 0 660 661early_recursion_flag: 662 .long 0 663 664int_msg: 665 .asciz "Unknown interrupt or fault at EIP %p %p %p\n" 666 667fault_msg: 668/* fault info: */ 669 .ascii "BUG: Int %d: CR2 %p\n" 670/* pusha regs: */ 671 .ascii " EDI %p ESI %p EBP %p ESP %p\n" 672 .ascii " EBX %p EDX %p ECX %p EAX %p\n" 673/* fault frame: */ 674 .ascii " err %p EIP %p CS %p flg %p\n" 675 .ascii "Stack: %p %p %p %p %p %p %p %p\n" 676 .ascii " %p %p %p %p %p %p %p %p\n" 677 .asciz " %p %p %p %p %p %p %p %p\n" 678 679#include "../../x86/xen/xen-head.S" 680 681/* 682 * The IDT and GDT 'descriptors' are a strange 48-bit object 683 * only used by the lidt and lgdt instructions. They are not 684 * like usual segment descriptors - they consist of a 16-bit 685 * segment size, and 32-bit linear address value: 686 */ 687 688.globl boot_gdt_descr 689.globl idt_descr 690 691 ALIGN 692# early boot GDT descriptor (must use 1:1 address mapping) 693 .word 0 # 32 bit align gdt_desc.address 694boot_gdt_descr: 695 .word __BOOT_DS+7 696 .long boot_gdt - __PAGE_OFFSET 697 698 .word 0 # 32-bit align idt_desc.address 699idt_descr: 700 .word IDT_ENTRIES*8-1 # idt contains 256 entries 701 .long idt_table 702 703# boot GDT descriptor (later on used by CPU#0): 704 .word 0 # 32 bit align gdt_desc.address 705ENTRY(early_gdt_descr) 706 .word GDT_ENTRIES*8-1 707 .long per_cpu__gdt_page /* Overwritten for secondary CPUs */ 708 709/* 710 * The boot_gdt must mirror the equivalent in setup.S and is 711 * used only for booting. 712 */ 713 .align L1_CACHE_BYTES 714ENTRY(boot_gdt) 715 .fill GDT_ENTRY_BOOT_CS,8,0 716 .quad 0x00cf9a000000ffff /* kernel 4GB code at 0x00000000 */ 717 .quad 0x00cf92000000ffff /* kernel 4GB data at 0x00000000 */ 718