arch/x86/kernel/head_32.S

   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_types.h>
  15 #include <asm/pgtable_types.h>
  16 #include <asm/cache.h>
  17 #include <asm/thread_info.h>
  18 #include <asm/asm-offsets.h>
  19 #include <asm/setup.h>
  20 #include <asm/processor-flags.h>
  21 #include <asm/msr-index.h>
  22 #include <asm/cpufeatures.h>
  23 #include <asm/percpu.h>
  24 #include <asm/nops.h>
  25 #include <asm/bootparam.h>
  26 #include <asm/export.h>
  27 #include <asm/pgtable_32.h>
  28 #include <asm/nospec-branch.h>
  29
  30 /* Physical address */
  31 #define pa(X) ((X) - __PAGE_OFFSET)
  32
  33 /*
  34  * References to members of the new_cpu_data structure.
  35  */
  36
  37 #define X86             new_cpu_data+CPUINFO_x86
  38 #define X86_VENDOR      new_cpu_data+CPUINFO_x86_vendor
  39 #define X86_MODEL       new_cpu_data+CPUINFO_x86_model
  40 #define X86_MASK        new_cpu_data+CPUINFO_x86_mask
  41 #define X86_HARD_MATH   new_cpu_data+CPUINFO_hard_math
  42 #define X86_CPUID       new_cpu_data+CPUINFO_cpuid_level
  43 #define X86_CAPABILITY  new_cpu_data+CPUINFO_x86_capability
  44 #define X86_VENDOR_ID   new_cpu_data+CPUINFO_x86_vendor_id
  45
  46
  47 #define SIZEOF_PTREGS 17*4
  48
  49 /*
  50  * Worst-case size of the kernel mapping we need to make:
  51  * a relocatable kernel can live anywhere in lowmem, so we need to be able
  52  * to map all of lowmem.
  53  */
  54 KERNEL_PAGES = LOWMEM_PAGES
  55
  56 INIT_MAP_SIZE = PAGE_TABLE_SIZE(KERNEL_PAGES) * PAGE_SIZE
  57 RESERVE_BRK(pagetables, INIT_MAP_SIZE)
  58
  59 /*
  60  * 32-bit kernel entrypoint; only used by the boot CPU.  On entry,
  61  * %esi points to the real-mode code as a 32-bit pointer.
  62  * CS and DS must be 4 GB flat segments, but we don't depend on
  63  * any particular GDT layout, because we load our own as soon as we
  64  * can.
  65  */
  66 __HEAD
  67 ENTRY(startup_32)
  68         movl pa(initial_stack),%ecx
  69
  70         /* test KEEP_SEGMENTS flag to see if the bootloader is asking
  71                 us to not reload segments */
  72         testb $KEEP_SEGMENTS, BP_loadflags(%esi)
  73         jnz 2f
  74
  75 /*
  76  * Set segments to known values.
  77  */
  78         lgdt pa(boot_gdt_descr)
  79         movl $(__BOOT_DS),%eax
  80         movl %eax,%ds
  81         movl %eax,%es
  82         movl %eax,%fs
  83         movl %eax,%gs
  84         movl %eax,%ss
  85 2:
  86         leal -__PAGE_OFFSET(%ecx),%esp
  87
  88 /*
  89  * Clear BSS first so that there are no surprises...
  90  */
  91         cld
  92         xorl %eax,%eax
  93         movl $pa(__bss_start),%edi
  94         movl $pa(__bss_stop),%ecx
  95         subl %edi,%ecx
  96         shrl $2,%ecx
  97         rep ; stosl
  98 /*
  99  * Copy bootup parameters out of the way.
 100  * Note: %esi still has the pointer to the real-mode data.
 101  * With the kexec as boot loader, parameter segment might be loaded beyond
 102  * kernel image and might not even be addressable by early boot page tables.
 103  * (kexec on panic case). Hence copy out the parameters before initializing
 104  * page tables.
 105  */
 106         movl $pa(boot_params),%edi
 107         movl $(PARAM_SIZE/4),%ecx
 108         cld
 109         rep
 110         movsl
 111         movl pa(boot_params) + NEW_CL_POINTER,%esi
 112         andl %esi,%esi
 113         jz 1f                   # No command line
 114         movl $pa(boot_command_line),%edi
 115         movl $(COMMAND_LINE_SIZE/4),%ecx
 116         rep
 117         movsl
 118 1:
 119
 120 #ifdef CONFIG_OLPC
 121         /* save OFW's pgdir table for later use when calling into OFW */
 122         movl %cr3, %eax
 123         movl %eax, pa(olpc_ofw_pgd)
 124 #endif
 125
 126 #ifdef CONFIG_MICROCODE
 127         /* Early load ucode on BSP. */
 128         call load_ucode_bsp
 129 #endif
 130
 131         /* Create early pagetables. */
 132         call  mk_early_pgtbl_32
 133
 134         /* Do early initialization of the fixmap area */
 135         movl $pa(initial_pg_fixmap)+PDE_IDENT_ATTR,%eax
 136 #ifdef  CONFIG_X86_PAE
 137 #define KPMDS (((-__PAGE_OFFSET) >> 30) & 3) /* Number of kernel PMDs */
 138         movl %eax,pa(initial_pg_pmd+0x1000*KPMDS-8)
 139 #else
 140         movl %eax,pa(initial_page_table+0xffc)
 141 #endif
 142
 143 #ifdef CONFIG_PARAVIRT
 144         /* This is can only trip for a broken bootloader... */
 145         cmpw $0x207, pa(boot_params + BP_version)
 146         jb .Ldefault_entry
 147
 148         /* Paravirt-compatible boot parameters.  Look to see what architecture
 149                 we're booting under. */
 150         movl pa(boot_params + BP_hardware_subarch), %eax
 151         cmpl $num_subarch_entries, %eax
 152         jae .Lbad_subarch
 153
 154         movl pa(subarch_entries)(,%eax,4), %eax
 155         subl $__PAGE_OFFSET, %eax
 156         ANNOTATE_RETPOLINE_SAFE
 157         jmp *%eax
 158
 159 .Lbad_subarch:
 160 WEAK(lguest_entry)
 161 WEAK(xen_entry)
 162         /* Unknown implementation; there's really
 163            nothing we can do at this point. */
 164         ud2a
 165
 166         __INITDATA
 167
 168 subarch_entries:
 169         .long .Ldefault_entry           /* normal x86/PC */
 170         .long lguest_entry              /* lguest hypervisor */
 171         .long xen_entry                 /* Xen hypervisor */
 172         .long .Ldefault_entry           /* Moorestown MID */
 173 num_subarch_entries = (. - subarch_entries) / 4
 174 .previous
 175 #else
 176         jmp .Ldefault_entry
 177 #endif /* CONFIG_PARAVIRT */
 178
 179 #ifdef CONFIG_HOTPLUG_CPU
 180 /*
 181  * Boot CPU0 entry point. It's called from play_dead(). Everything has been set
 182  * up already except stack. We just set up stack here. Then call
 183  * start_secondary().
 184  */
 185 ENTRY(start_cpu0)
 186         movl initial_stack, %ecx
 187         movl %ecx, %esp
 188         call *(initial_code)
 189 1:      jmp 1b
 190 ENDPROC(start_cpu0)
 191 #endif
 192
 193 /*
 194  * Non-boot CPU entry point; entered from trampoline.S
 195  * We can't lgdt here, because lgdt itself uses a data segment, but
 196  * we know the trampoline has already loaded the boot_gdt for us.
 197  *
 198  * If cpu hotplug is not supported then this code can go in init section
 199  * which will be freed later
 200  */
 201 ENTRY(startup_32_smp)
 202         cld
 203         movl $(__BOOT_DS),%eax
 204         movl %eax,%ds
 205         movl %eax,%es
 206         movl %eax,%fs
 207         movl %eax,%gs
 208         movl pa(initial_stack),%ecx
 209         movl %eax,%ss
 210         leal -__PAGE_OFFSET(%ecx),%esp
 211
 212 #ifdef CONFIG_MICROCODE
 213         /* Early load ucode on AP. */
 214         call load_ucode_ap
 215 #endif
 216
 217 .Ldefault_entry:
 218         movl $(CR0_STATE & ~X86_CR0_PG),%eax
 219         movl %eax,%cr0
 220
 221 /*
 222  * We want to start out with EFLAGS unambiguously cleared. Some BIOSes leave
 223  * bits like NT set. This would confuse the debugger if this code is traced. So
 224  * initialize them properly now before switching to protected mode. That means
 225  * DF in particular (even though we have cleared it earlier after copying the
 226  * command line) because GCC expects it.
 227  */
 228         pushl $0
 229         popfl
 230
 231 /*
 232  * New page tables may be in 4Mbyte page mode and may be using the global pages.
 233  *
 234  * NOTE! If we are on a 486 we may have no cr4 at all! Specifically, cr4 exists
 235  * if and only if CPUID exists and has flags other than the FPU flag set.
 236  */
 237         movl $-1,pa(X86_CPUID)          # preset CPUID level
 238         movl $X86_EFLAGS_ID,%ecx
 239         pushl %ecx
 240         popfl                           # set EFLAGS=ID
 241         pushfl
 242         popl %eax                       # get EFLAGS
 243         testl $X86_EFLAGS_ID,%eax       # did EFLAGS.ID remained set?
 244         jz .Lenable_paging              # hw disallowed setting of ID bit
 245                                         # which means no CPUID and no CR4
 246
 247         xorl %eax,%eax
 248         cpuid
 249         movl %eax,pa(X86_CPUID)         # save largest std CPUID function
 250
 251         movl $1,%eax
 252         cpuid
 253         andl $~1,%edx                   # Ignore CPUID.FPU
 254         jz .Lenable_paging              # No flags or only CPUID.FPU = no CR4
 255
 256         movl pa(mmu_cr4_features),%eax
 257         movl %eax,%cr4
 258
 259         testb $X86_CR4_PAE, %al         # check if PAE is enabled
 260         jz .Lenable_paging
 261
 262         /* Check if extended functions are implemented */
 263         movl $0x80000000, %eax
 264         cpuid
 265         /* Value must be in the range 0x80000001 to 0x8000ffff */
 266         subl $0x80000001, %eax
 267         cmpl $(0x8000ffff-0x80000001), %eax
 268         ja .Lenable_paging
 269
 270         /* Clear bogus XD_DISABLE bits */
 271         call verify_cpu
 272
 273         mov $0x80000001, %eax
 274         cpuid
 275         /* Execute Disable bit supported? */
 276         btl $(X86_FEATURE_NX & 31), %edx
 277         jnc .Lenable_paging
 278
 279         /* Setup EFER (Extended Feature Enable Register) */
 280         movl $MSR_EFER, %ecx
 281         rdmsr
 282
 283         btsl $_EFER_NX, %eax
 284         /* Make changes effective */
 285         wrmsr
 286
 287 .Lenable_paging:
 288
 289 /*
 290  * Enable paging
 291  */
 292         movl $pa(initial_page_table), %eax
 293         movl %eax,%cr3          /* set the page table pointer.. */
 294         movl $CR0_STATE,%eax
 295         movl %eax,%cr0          /* ..and set paging (PG) bit */
 296         ljmp $__BOOT_CS,$1f     /* Clear prefetch and normalize %eip */
 297 1:
 298         /* Shift the stack pointer to a virtual address */
 299         addl $__PAGE_OFFSET, %esp
 300
 301 /*
 302  * start system 32-bit setup. We need to re-do some of the things done
 303  * in 16-bit mode for the "real" operations.
 304  */
 305         movl setup_once_ref,%eax
 306         andl %eax,%eax
 307         jz 1f                           # Did we do this already?
 308         ANNOTATE_RETPOLINE_SAFE
 309         call *%eax
 310 1:
 311
 312 /*
 313  * Check if it is 486
 314  */
 315         movb $4,X86                     # at least 486
 316         cmpl $-1,X86_CPUID
 317         je .Lis486
 318
 319         /* get vendor info */
 320         xorl %eax,%eax                  # call CPUID with 0 -> return vendor ID
 321         cpuid
 322         movl %eax,X86_CPUID             # save CPUID level
 323         movl %ebx,X86_VENDOR_ID         # lo 4 chars
 324         movl %edx,X86_VENDOR_ID+4       # next 4 chars
 325         movl %ecx,X86_VENDOR_ID+8       # last 4 chars
 326
 327         orl %eax,%eax                   # do we have processor info as well?
 328         je .Lis486
 329
 330         movl $1,%eax            # Use the CPUID instruction to get CPU type
 331         cpuid
 332         movb %al,%cl            # save reg for future use
 333         andb $0x0f,%ah          # mask processor family
 334         movb %ah,X86
 335         andb $0xf0,%al          # mask model
 336         shrb $4,%al
 337         movb %al,X86_MODEL
 338         andb $0x0f,%cl          # mask mask revision
 339         movb %cl,X86_MASK
 340         movl %edx,X86_CAPABILITY
 341
 342 .Lis486:
 343         movl $0x50022,%ecx      # set AM, WP, NE and MP
 344         movl %cr0,%eax
 345         andl $0x80000011,%eax   # Save PG,PE,ET
 346         orl %ecx,%eax
 347         movl %eax,%cr0
 348
 349         lgdt early_gdt_descr
 350         lidt idt_descr
 351         ljmp $(__KERNEL_CS),$1f
 352 1:      movl $(__KERNEL_DS),%eax        # reload all the segment registers
 353         movl %eax,%ss                   # after changing gdt.
 354
 355         movl $(__USER_DS),%eax          # DS/ES contains default USER segment
 356         movl %eax,%ds
 357         movl %eax,%es
 358
 359         movl $(__KERNEL_PERCPU), %eax
 360         movl %eax,%fs                   # set this cpu's percpu
 361
 362         movl $(__KERNEL_STACK_CANARY),%eax
 363         movl %eax,%gs
 364
 365         xorl %eax,%eax                  # Clear LDT
 366         lldt %ax
 367
 368         call *(initial_code)
 369 1:      jmp 1b
 370 ENDPROC(startup_32_smp)
 371
 372 #include "verify_cpu.S"
 373
 374 /*
 375  *  setup_once
 376  *
 377  *  The setup work we only want to run on the BSP.
 378  *
 379  *  Warning: %esi is live across this function.
 380  */
 381 __INIT
 382 setup_once:
 383         /*
 384          * Set up a idt with 256 interrupt gates that push zero if there
 385          * is no error code and then jump to early_idt_handler_common.
 386          * It doesn't actually load the idt - that needs to be done on
 387          * each CPU. Interrupts are enabled elsewhere, when we can be
 388          * relatively sure everything is ok.
 389          */
 390
 391         movl $idt_table,%edi
 392         movl $early_idt_handler_array,%eax
 393         movl $NUM_EXCEPTION_VECTORS,%ecx
 394 1:
 395         movl %eax,(%edi)
 396         movl %eax,4(%edi)
 397         /* interrupt gate, dpl=0, present */
 398         movl $(0x8E000000 + __KERNEL_CS),2(%edi)
 399         addl $EARLY_IDT_HANDLER_SIZE,%eax
 400         addl $8,%edi
 401         loop 1b
 402
 403         movl $256 - NUM_EXCEPTION_VECTORS,%ecx
 404         movl $ignore_int,%edx
 405         movl $(__KERNEL_CS << 16),%eax
 406         movw %dx,%ax            /* selector = 0x0010 = cs */
 407         movw $0x8E00,%dx        /* interrupt gate - dpl=0, present */
 408 2:
 409         movl %eax,(%edi)
 410         movl %edx,4(%edi)
 411         addl $8,%edi
 412         loop 2b
 413
 414 #ifdef CONFIG_CC_STACKPROTECTOR
 415         /*
 416          * Configure the stack canary. The linker can't handle this by
 417          * relocation.  Manually set base address in stack canary
 418          * segment descriptor.
 419          */
 420         movl $gdt_page,%eax
 421         movl $stack_canary,%ecx
 422         movw %cx, 8 * GDT_ENTRY_STACK_CANARY + 2(%eax)
 423         shrl $16, %ecx
 424         movb %cl, 8 * GDT_ENTRY_STACK_CANARY + 4(%eax)
 425         movb %ch, 8 * GDT_ENTRY_STACK_CANARY + 7(%eax)
 426 #endif
 427
 428         andl $0,setup_once_ref  /* Once is enough, thanks */
 429         ret
 430
 431 ENTRY(early_idt_handler_array)
 432         # 36(%esp) %eflags
 433         # 32(%esp) %cs
 434         # 28(%esp) %eip
 435         # 24(%rsp) error code
 436         i = 0
 437         .rept NUM_EXCEPTION_VECTORS
 438         .if ((EXCEPTION_ERRCODE_MASK >> i) & 1) == 0
 439         pushl $0                # Dummy error code, to make stack frame uniform
 440         .endif
 441         pushl $i                # 20(%esp) Vector number
 442         jmp early_idt_handler_common
 443         i = i + 1
 444         .fill early_idt_handler_array + i*EARLY_IDT_HANDLER_SIZE - ., 1, 0xcc
 445         .endr
 446 ENDPROC(early_idt_handler_array)
 447
 448 early_idt_handler_common:
 449         /*
 450          * The stack is the hardware frame, an error code or zero, and the
 451          * vector number.
 452          */
 453         cld
 454
 455         incl %ss:early_recursion_flag
 456
 457         /* The vector number is in pt_regs->gs */
 458
 459         cld
 460         pushl   %fs             /* pt_regs->fs */
 461         movw    $0, 2(%esp)     /* clear high bits (some CPUs leave garbage) */
 462         pushl   %es             /* pt_regs->es */
 463         movw    $0, 2(%esp)     /* clear high bits (some CPUs leave garbage) */
 464         pushl   %ds             /* pt_regs->ds */
 465         movw    $0, 2(%esp)     /* clear high bits (some CPUs leave garbage) */
 466         pushl   %eax            /* pt_regs->ax */
 467         pushl   %ebp            /* pt_regs->bp */
 468         pushl   %edi            /* pt_regs->di */
 469         pushl   %esi            /* pt_regs->si */
 470         pushl   %edx            /* pt_regs->dx */
 471         pushl   %ecx            /* pt_regs->cx */
 472         pushl   %ebx            /* pt_regs->bx */
 473
 474         /* Fix up DS and ES */
 475         movl    $(__KERNEL_DS), %ecx
 476         movl    %ecx, %ds
 477         movl    %ecx, %es
 478
 479         /* Load the vector number into EDX */
 480         movl    PT_GS(%esp), %edx
 481
 482         /* Load GS into pt_regs->gs and clear high bits */
 483         movw    %gs, PT_GS(%esp)
 484         movw    $0, PT_GS+2(%esp)
 485
 486         movl    %esp, %eax      /* args are pt_regs (EAX), trapnr (EDX) */
 487         call    early_fixup_exception
 488
 489         popl    %ebx            /* pt_regs->bx */
 490         popl    %ecx            /* pt_regs->cx */
 491         popl    %edx            /* pt_regs->dx */
 492         popl    %esi            /* pt_regs->si */
 493         popl    %edi            /* pt_regs->di */
 494         popl    %ebp            /* pt_regs->bp */
 495         popl    %eax            /* pt_regs->ax */
 496         popl    %ds             /* pt_regs->ds */
 497         popl    %es             /* pt_regs->es */
 498         popl    %fs             /* pt_regs->fs */
 499         popl    %gs             /* pt_regs->gs */
 500         decl    %ss:early_recursion_flag
 501         addl    $4, %esp        /* pop pt_regs->orig_ax */
 502         iret
 503 ENDPROC(early_idt_handler_common)
 504
 505 /* This is the default interrupt "handler" :-) */
 506         ALIGN
 507 ignore_int:
 508         cld
 509 #ifdef CONFIG_PRINTK
 510         pushl %eax
 511         pushl %ecx
 512         pushl %edx
 513         pushl %es
 514         pushl %ds
 515         movl $(__KERNEL_DS),%eax
 516         movl %eax,%ds
 517         movl %eax,%es
 518         cmpl $2,early_recursion_flag
 519         je hlt_loop
 520         incl early_recursion_flag
 521         pushl 16(%esp)
 522         pushl 24(%esp)
 523         pushl 32(%esp)
 524         pushl 40(%esp)
 525         pushl $int_msg
 526         call printk
 527
 528         call dump_stack
 529
 530         addl $(5*4),%esp
 531         popl %ds
 532         popl %es
 533         popl %edx
 534         popl %ecx
 535         popl %eax
 536 #endif
 537         iret
 538
 539 hlt_loop:
 540         hlt
 541         jmp hlt_loop
 542 ENDPROC(ignore_int)
 543 __INITDATA
 544         .align 4
 545 GLOBAL(early_recursion_flag)
 546         .long 0
 547
 548 __REFDATA
 549         .align 4
 550 ENTRY(initial_code)
 551         .long i386_start_kernel
 552 ENTRY(setup_once_ref)
 553         .long setup_once
 554
 555 /*
 556  * BSS section
 557  */
 558 __PAGE_ALIGNED_BSS
 559         .align PAGE_SIZE
 560 #ifdef CONFIG_X86_PAE
 561 .globl initial_pg_pmd
 562 initial_pg_pmd:
 563         .fill 1024*KPMDS,4,0
 564 #else
 565 .globl initial_page_table
 566 initial_page_table:
 567         .fill 1024,4,0
 568 #endif
 569 initial_pg_fixmap:
 570         .fill 1024,4,0
 571 .globl empty_zero_page
 572 empty_zero_page:
 573         .fill 4096,1,0
 574 .globl swapper_pg_dir
 575 swapper_pg_dir:
 576         .fill 1024,4,0
 577 EXPORT_SYMBOL(empty_zero_page)
 578
 579 /*
 580  * This starts the data section.
 581  */
 582 #ifdef CONFIG_X86_PAE
 583 __PAGE_ALIGNED_DATA
 584         /* Page-aligned for the benefit of paravirt? */
 585         .align PAGE_SIZE
 586 ENTRY(initial_page_table)
 587         .long   pa(initial_pg_pmd+PGD_IDENT_ATTR),0     /* low identity map */
 588 # if KPMDS == 3
 589         .long   pa(initial_pg_pmd+PGD_IDENT_ATTR),0
 590         .long   pa(initial_pg_pmd+PGD_IDENT_ATTR+0x1000),0
 591         .long   pa(initial_pg_pmd+PGD_IDENT_ATTR+0x2000),0
 592 # elif KPMDS == 2
 593         .long   0,0
 594         .long   pa(initial_pg_pmd+PGD_IDENT_ATTR),0
 595         .long   pa(initial_pg_pmd+PGD_IDENT_ATTR+0x1000),0
 596 # elif KPMDS == 1
 597         .long   0,0
 598         .long   0,0
 599         .long   pa(initial_pg_pmd+PGD_IDENT_ATTR),0
 600 # else
 601 #  error "Kernel PMDs should be 1, 2 or 3"
 602 # endif
 603         .align PAGE_SIZE                /* needs to be page-sized too */
 604 #endif
 605
 606 .data
 607 .balign 4
 608 ENTRY(initial_stack)
 609         /*
 610          * The SIZEOF_PTREGS gap is a convention which helps the in-kernel
 611          * unwinder reliably detect the end of the stack.
 612          */
 613         .long init_thread_union + THREAD_SIZE - SIZEOF_PTREGS - \
 614               TOP_OF_KERNEL_STACK_PADDING;
 615
 616 __INITRODATA
 617 int_msg:
 618         .asciz "Unknown interrupt or fault at: %p %p %p\n"
 619
 620 #include "../../x86/xen/xen-head.S"
 621
 622 /*
 623  * The IDT and GDT 'descriptors' are a strange 48-bit object
 624  * only used by the lidt and lgdt instructions. They are not
 625  * like usual segment descriptors - they consist of a 16-bit
 626  * segment size, and 32-bit linear address value:
 627  */
 628
 629         .data
 630 .globl boot_gdt_descr
 631 .globl idt_descr
 632
 633         ALIGN
 634 # early boot GDT descriptor (must use 1:1 address mapping)
 635         .word 0                         # 32 bit align gdt_desc.address
 636 boot_gdt_descr:
 637         .word __BOOT_DS+7
 638         .long boot_gdt - __PAGE_OFFSET
 639
 640         .word 0                         # 32-bit align idt_desc.address
 641 idt_descr:
 642         .word IDT_ENTRIES*8-1           # idt contains 256 entries
 643         .long idt_table
 644
 645 # boot GDT descriptor (later on used by CPU#0):
 646         .word 0                         # 32 bit align gdt_desc.address
 647 ENTRY(early_gdt_descr)
 648         .word GDT_ENTRIES*8-1
 649         .long gdt_page                  /* Overwritten for secondary CPUs */
 650
 651 /*
 652  * The boot_gdt must mirror the equivalent in setup.S and is
 653  * used only for booting.
 654  */
 655         .align L1_CACHE_BYTES
 656 ENTRY(boot_gdt)
 657         .fill GDT_ENTRY_BOOT_CS,8,0
 658         .quad 0x00cf9a000000ffff        /* kernel 4GB code at 0x00000000 */
 659         .quad 0x00cf92000000ffff        /* kernel 4GB data at 0x00000000 */