xref: /openbmc/linux/arch/x86/kernel/head_32.S (revision e7065e20) 
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/cpufeature.h>
23#include <asm/percpu.h>
24
25/* Physical address */
26#define pa(X) ((X) - __PAGE_OFFSET)
27
28/*
29 * References to members of the new_cpu_data structure.
30 */
31
32#define X86		new_cpu_data+CPUINFO_x86
33#define X86_VENDOR	new_cpu_data+CPUINFO_x86_vendor
34#define X86_MODEL	new_cpu_data+CPUINFO_x86_model
35#define X86_MASK	new_cpu_data+CPUINFO_x86_mask
36#define X86_HARD_MATH	new_cpu_data+CPUINFO_hard_math
37#define X86_CPUID	new_cpu_data+CPUINFO_cpuid_level
38#define X86_CAPABILITY	new_cpu_data+CPUINFO_x86_capability
39#define X86_VENDOR_ID	new_cpu_data+CPUINFO_x86_vendor_id
40
41/*
42 * This is how much memory in addition to the memory covered up to
43 * and including _end we need mapped initially.
44 * We need:
45 *     (KERNEL_IMAGE_SIZE/4096) / 1024 pages (worst case, non PAE)
46 *     (KERNEL_IMAGE_SIZE/4096) / 512 + 4 pages (worst case for PAE)
47 *
48 * Modulo rounding, each megabyte assigned here requires a kilobyte of
49 * memory, which is currently unreclaimed.
50 *
51 * This should be a multiple of a page.
52 *
53 * KERNEL_IMAGE_SIZE should be greater than pa(_end)
54 * and small than max_low_pfn, otherwise will waste some page table entries
55 */
56
57#if PTRS_PER_PMD > 1
58#define PAGE_TABLE_SIZE(pages) (((pages) / PTRS_PER_PMD) + PTRS_PER_PGD)
59#else
60#define PAGE_TABLE_SIZE(pages) ((pages) / PTRS_PER_PGD)
61#endif
62
63/* Number of possible pages in the lowmem region */
64LOWMEM_PAGES = (((1<<32) - __PAGE_OFFSET) >> PAGE_SHIFT)
65
66/* Enough space to fit pagetables for the low memory linear map */
67MAPPING_BEYOND_END = PAGE_TABLE_SIZE(LOWMEM_PAGES) << PAGE_SHIFT
68
69/*
70 * Worst-case size of the kernel mapping we need to make:
71 * a relocatable kernel can live anywhere in lowmem, so we need to be able
72 * to map all of lowmem.
73 */
74KERNEL_PAGES = LOWMEM_PAGES
75
76INIT_MAP_SIZE = PAGE_TABLE_SIZE(KERNEL_PAGES) * PAGE_SIZE
77RESERVE_BRK(pagetables, INIT_MAP_SIZE)
78
79/*
80 * 32-bit kernel entrypoint; only used by the boot CPU.  On entry,
81 * %esi points to the real-mode code as a 32-bit pointer.
82 * CS and DS must be 4 GB flat segments, but we don't depend on
83 * any particular GDT layout, because we load our own as soon as we
84 * can.
85 */
86__HEAD
87ENTRY(startup_32)
88	movl pa(stack_start),%ecx
89
90	/* test KEEP_SEGMENTS flag to see if the bootloader is asking
91		us to not reload segments */
92	testb $(1<<6), BP_loadflags(%esi)
93	jnz 2f
94
95/*
96 * Set segments to known values.
97 */
98	lgdt pa(boot_gdt_descr)
99	movl $(__BOOT_DS),%eax
100	movl %eax,%ds
101	movl %eax,%es
102	movl %eax,%fs
103	movl %eax,%gs
104	movl %eax,%ss
1052:
106	leal -__PAGE_OFFSET(%ecx),%esp
107
108/*
109 * Clear BSS first so that there are no surprises...
110 */
111	cld
112	xorl %eax,%eax
113	movl $pa(__bss_start),%edi
114	movl $pa(__bss_stop),%ecx
115	subl %edi,%ecx
116	shrl $2,%ecx
117	rep ; stosl
118/*
119 * Copy bootup parameters out of the way.
120 * Note: %esi still has the pointer to the real-mode data.
121 * With the kexec as boot loader, parameter segment might be loaded beyond
122 * kernel image and might not even be addressable by early boot page tables.
123 * (kexec on panic case). Hence copy out the parameters before initializing
124 * page tables.
125 */
126	movl $pa(boot_params),%edi
127	movl $(PARAM_SIZE/4),%ecx
128	cld
129	rep
130	movsl
131	movl pa(boot_params) + NEW_CL_POINTER,%esi
132	andl %esi,%esi
133	jz 1f			# No command line
134	movl $pa(boot_command_line),%edi
135	movl $(COMMAND_LINE_SIZE/4),%ecx
136	rep
137	movsl
1381:
139
140#ifdef CONFIG_OLPC
141	/* save OFW's pgdir table for later use when calling into OFW */
142	movl %cr3, %eax
143	movl %eax, pa(olpc_ofw_pgd)
144#endif
145
146/*
147 * Initialize page tables.  This creates a PDE and a set of page
148 * tables, which are located immediately beyond __brk_base.  The variable
149 * _brk_end is set up to point to the first "safe" location.
150 * Mappings are created both at virtual address 0 (identity mapping)
151 * and PAGE_OFFSET for up to _end.
152 */
153#ifdef CONFIG_X86_PAE
154
155	/*
156	 * In PAE mode initial_page_table is statically defined to contain
157	 * enough entries to cover the VMSPLIT option (that is the top 1, 2 or 3
158	 * entries). The identity mapping is handled by pointing two PGD entries
159	 * to the first kernel PMD.
160	 *
161	 * Note the upper half of each PMD or PTE are always zero at this stage.
162	 */
163
164#define KPMDS (((-__PAGE_OFFSET) >> 30) & 3) /* Number of kernel PMDs */
165
166	xorl %ebx,%ebx				/* %ebx is kept at zero */
167
168	movl $pa(__brk_base), %edi
169	movl $pa(initial_pg_pmd), %edx
170	movl $PTE_IDENT_ATTR, %eax
17110:
172	leal PDE_IDENT_ATTR(%edi),%ecx		/* Create PMD entry */
173	movl %ecx,(%edx)			/* Store PMD entry */
174						/* Upper half already zero */
175	addl $8,%edx
176	movl $512,%ecx
17711:
178	stosl
179	xchgl %eax,%ebx
180	stosl
181	xchgl %eax,%ebx
182	addl $0x1000,%eax
183	loop 11b
184
185	/*
186	 * End condition: we must map up to the end + MAPPING_BEYOND_END.
187	 */
188	movl $pa(_end) + MAPPING_BEYOND_END + PTE_IDENT_ATTR, %ebp
189	cmpl %ebp,%eax
190	jb 10b
1911:
192	addl $__PAGE_OFFSET, %edi
193	movl %edi, pa(_brk_end)
194	shrl $12, %eax
195	movl %eax, pa(max_pfn_mapped)
196
197	/* Do early initialization of the fixmap area */
198	movl $pa(initial_pg_fixmap)+PDE_IDENT_ATTR,%eax
199	movl %eax,pa(initial_pg_pmd+0x1000*KPMDS-8)
200#else	/* Not PAE */
201
202page_pde_offset = (__PAGE_OFFSET >> 20);
203
204	movl $pa(__brk_base), %edi
205	movl $pa(initial_page_table), %edx
206	movl $PTE_IDENT_ATTR, %eax
20710:
208	leal PDE_IDENT_ATTR(%edi),%ecx		/* Create PDE entry */
209	movl %ecx,(%edx)			/* Store identity PDE entry */
210	movl %ecx,page_pde_offset(%edx)		/* Store kernel PDE entry */
211	addl $4,%edx
212	movl $1024, %ecx
21311:
214	stosl
215	addl $0x1000,%eax
216	loop 11b
217	/*
218	 * End condition: we must map up to the end + MAPPING_BEYOND_END.
219	 */
220	movl $pa(_end) + MAPPING_BEYOND_END + PTE_IDENT_ATTR, %ebp
221	cmpl %ebp,%eax
222	jb 10b
223	addl $__PAGE_OFFSET, %edi
224	movl %edi, pa(_brk_end)
225	shrl $12, %eax
226	movl %eax, pa(max_pfn_mapped)
227
228	/* Do early initialization of the fixmap area */
229	movl $pa(initial_pg_fixmap)+PDE_IDENT_ATTR,%eax
230	movl %eax,pa(initial_page_table+0xffc)
231#endif
232
233#ifdef CONFIG_PARAVIRT
234	/* This is can only trip for a broken bootloader... */
235	cmpw $0x207, pa(boot_params + BP_version)
236	jb default_entry
237
238	/* Paravirt-compatible boot parameters.  Look to see what architecture
239		we're booting under. */
240	movl pa(boot_params + BP_hardware_subarch), %eax
241	cmpl $num_subarch_entries, %eax
242	jae bad_subarch
243
244	movl pa(subarch_entries)(,%eax,4), %eax
245	subl $__PAGE_OFFSET, %eax
246	jmp *%eax
247
248bad_subarch:
249WEAK(lguest_entry)
250WEAK(xen_entry)
251	/* Unknown implementation; there's really
252	   nothing we can do at this point. */
253	ud2a
254
255	__INITDATA
256
257subarch_entries:
258	.long default_entry		/* normal x86/PC */
259	.long lguest_entry		/* lguest hypervisor */
260	.long xen_entry			/* Xen hypervisor */
261	.long default_entry		/* Moorestown MID */
262num_subarch_entries = (. - subarch_entries) / 4
263.previous
264#else
265	jmp default_entry
266#endif /* CONFIG_PARAVIRT */
267
268/*
269 * Non-boot CPU entry point; entered from trampoline.S
270 * We can't lgdt here, because lgdt itself uses a data segment, but
271 * we know the trampoline has already loaded the boot_gdt for us.
272 *
273 * If cpu hotplug is not supported then this code can go in init section
274 * which will be freed later
275 */
276
277__CPUINIT
278
279#ifdef CONFIG_SMP
280ENTRY(startup_32_smp)
281	cld
282	movl $(__BOOT_DS),%eax
283	movl %eax,%ds
284	movl %eax,%es
285	movl %eax,%fs
286	movl %eax,%gs
287	movl pa(stack_start),%ecx
288	movl %eax,%ss
289	leal -__PAGE_OFFSET(%ecx),%esp
290#endif /* CONFIG_SMP */
291default_entry:
292
293/*
294 *	New page tables may be in 4Mbyte page mode and may
295 *	be using the global pages.
296 *
297 *	NOTE! If we are on a 486 we may have no cr4 at all!
298 *	So we do not try to touch it unless we really have
299 *	some bits in it to set.  This won't work if the BSP
300 *	implements cr4 but this AP does not -- very unlikely
301 *	but be warned!  The same applies to the pse feature
302 *	if not equally supported. --macro
303 *
304 *	NOTE! We have to correct for the fact that we're
305 *	not yet offset PAGE_OFFSET..
306 */
307#define cr4_bits pa(mmu_cr4_features)
308	movl cr4_bits,%edx
309	andl %edx,%edx
310	jz 6f
311	movl %cr4,%eax		# Turn on paging options (PSE,PAE,..)
312	orl %edx,%eax
313	movl %eax,%cr4
314
315	testb $X86_CR4_PAE, %al		# check if PAE is enabled
316	jz 6f
317
318	/* Check if extended functions are implemented */
319	movl $0x80000000, %eax
320	cpuid
321	/* Value must be in the range 0x80000001 to 0x8000ffff */
322	subl $0x80000001, %eax
323	cmpl $(0x8000ffff-0x80000001), %eax
324	ja 6f
325
326	/* Clear bogus XD_DISABLE bits */
327	call verify_cpu
328
329	mov $0x80000001, %eax
330	cpuid
331	/* Execute Disable bit supported? */
332	btl $(X86_FEATURE_NX & 31), %edx
333	jnc 6f
334
335	/* Setup EFER (Extended Feature Enable Register) */
336	movl $MSR_EFER, %ecx
337	rdmsr
338
339	btsl $_EFER_NX, %eax
340	/* Make changes effective */
341	wrmsr
342
3436:
344
345/*
346 * Enable paging
347 */
348	movl $pa(initial_page_table), %eax
349	movl %eax,%cr3		/* set the page table pointer.. */
350	movl %cr0,%eax
351	orl  $X86_CR0_PG,%eax
352	movl %eax,%cr0		/* ..and set paging (PG) bit */
353	ljmp $__BOOT_CS,$1f	/* Clear prefetch and normalize %eip */
3541:
355	/* Shift the stack pointer to a virtual address */
356	addl $__PAGE_OFFSET, %esp
357
358/*
359 * Initialize eflags.  Some BIOS's leave bits like NT set.  This would
360 * confuse the debugger if this code is traced.
361 * XXX - best to initialize before switching to protected mode.
362 */
363	pushl $0
364	popfl
365
366#ifdef CONFIG_SMP
367	cmpb $0, ready
368	jnz checkCPUtype
369#endif /* CONFIG_SMP */
370
371/*
372 * start system 32-bit setup. We need to re-do some of the things done
373 * in 16-bit mode for the "real" operations.
374 */
375	call setup_idt
376
377checkCPUtype:
378
379	movl $-1,X86_CPUID		#  -1 for no CPUID initially
380
381/* check if it is 486 or 386. */
382/*
383 * XXX - this does a lot of unnecessary setup.  Alignment checks don't
384 * apply at our cpl of 0 and the stack ought to be aligned already, and
385 * we don't need to preserve eflags.
386 */
387
388	movb $3,X86		# at least 386
389	pushfl			# push EFLAGS
390	popl %eax		# get EFLAGS
391	movl %eax,%ecx		# save original EFLAGS
392	xorl $0x240000,%eax	# flip AC and ID bits in EFLAGS
393	pushl %eax		# copy to EFLAGS
394	popfl			# set EFLAGS
395	pushfl			# get new EFLAGS
396	popl %eax		# put it in eax
397	xorl %ecx,%eax		# change in flags
398	pushl %ecx		# restore original EFLAGS
399	popfl
400	testl $0x40000,%eax	# check if AC bit changed
401	je is386
402
403	movb $4,X86		# at least 486
404	testl $0x200000,%eax	# check if ID bit changed
405	je is486
406
407	/* get vendor info */
408	xorl %eax,%eax			# call CPUID with 0 -> return vendor ID
409	cpuid
410	movl %eax,X86_CPUID		# save CPUID level
411	movl %ebx,X86_VENDOR_ID		# lo 4 chars
412	movl %edx,X86_VENDOR_ID+4	# next 4 chars
413	movl %ecx,X86_VENDOR_ID+8	# last 4 chars
414
415	orl %eax,%eax			# do we have processor info as well?
416	je is486
417
418	movl $1,%eax		# Use the CPUID instruction to get CPU type
419	cpuid
420	movb %al,%cl		# save reg for future use
421	andb $0x0f,%ah		# mask processor family
422	movb %ah,X86
423	andb $0xf0,%al		# mask model
424	shrb $4,%al
425	movb %al,X86_MODEL
426	andb $0x0f,%cl		# mask mask revision
427	movb %cl,X86_MASK
428	movl %edx,X86_CAPABILITY
429
430is486:	movl $0x50022,%ecx	# set AM, WP, NE and MP
431	jmp 2f
432
433is386:	movl $2,%ecx		# set MP
4342:	movl %cr0,%eax
435	andl $0x80000011,%eax	# Save PG,PE,ET
436	orl %ecx,%eax
437	movl %eax,%cr0
438
439	call check_x87
440	lgdt early_gdt_descr
441	lidt idt_descr
442	ljmp $(__KERNEL_CS),$1f
4431:	movl $(__KERNEL_DS),%eax	# reload all the segment registers
444	movl %eax,%ss			# after changing gdt.
445
446	movl $(__USER_DS),%eax		# DS/ES contains default USER segment
447	movl %eax,%ds
448	movl %eax,%es
449
450	movl $(__KERNEL_PERCPU), %eax
451	movl %eax,%fs			# set this cpu's percpu
452
453#ifdef CONFIG_CC_STACKPROTECTOR
454	/*
455	 * The linker can't handle this by relocation.  Manually set
456	 * base address in stack canary segment descriptor.
457	 */
458	cmpb $0,ready
459	jne 1f
460	movl $gdt_page,%eax
461	movl $stack_canary,%ecx
462	movw %cx, 8 * GDT_ENTRY_STACK_CANARY + 2(%eax)
463	shrl $16, %ecx
464	movb %cl, 8 * GDT_ENTRY_STACK_CANARY + 4(%eax)
465	movb %ch, 8 * GDT_ENTRY_STACK_CANARY + 7(%eax)
4661:
467#endif
468	movl $(__KERNEL_STACK_CANARY),%eax
469	movl %eax,%gs
470
471	xorl %eax,%eax			# Clear LDT
472	lldt %ax
473
474	cld			# gcc2 wants the direction flag cleared at all times
475	pushl $0		# fake return address for unwinder
476	movb $1, ready
477	jmp *(initial_code)
478
479/*
480 * We depend on ET to be correct. This checks for 287/387.
481 */
482check_x87:
483	movb $0,X86_HARD_MATH
484	clts
485	fninit
486	fstsw %ax
487	cmpb $0,%al
488	je 1f
489	movl %cr0,%eax		/* no coprocessor: have to set bits */
490	xorl $4,%eax		/* set EM */
491	movl %eax,%cr0
492	ret
493	ALIGN
4941:	movb $1,X86_HARD_MATH
495	.byte 0xDB,0xE4		/* fsetpm for 287, ignored by 387 */
496	ret
497
498/*
499 *  setup_idt
500 *
501 *  sets up a idt with 256 entries pointing to
502 *  ignore_int, interrupt gates. It doesn't actually load
503 *  idt - that can be done only after paging has been enabled
504 *  and the kernel moved to PAGE_OFFSET. Interrupts
505 *  are enabled elsewhere, when we can be relatively
506 *  sure everything is ok.
507 *
508 *  Warning: %esi is live across this function.
509 */
510setup_idt:
511	lea ignore_int,%edx
512	movl $(__KERNEL_CS << 16),%eax
513	movw %dx,%ax		/* selector = 0x0010 = cs */
514	movw $0x8E00,%dx	/* interrupt gate - dpl=0, present */
515
516	lea idt_table,%edi
517	mov $256,%ecx
518rp_sidt:
519	movl %eax,(%edi)
520	movl %edx,4(%edi)
521	addl $8,%edi
522	dec %ecx
523	jne rp_sidt
524
525.macro	set_early_handler handler,trapno
526	lea \handler,%edx
527	movl $(__KERNEL_CS << 16),%eax
528	movw %dx,%ax
529	movw $0x8E00,%dx	/* interrupt gate - dpl=0, present */
530	lea idt_table,%edi
531	movl %eax,8*\trapno(%edi)
532	movl %edx,8*\trapno+4(%edi)
533.endm
534
535	set_early_handler handler=early_divide_err,trapno=0
536	set_early_handler handler=early_illegal_opcode,trapno=6
537	set_early_handler handler=early_protection_fault,trapno=13
538	set_early_handler handler=early_page_fault,trapno=14
539
540	ret
541
542early_divide_err:
543	xor %edx,%edx
544	pushl $0	/* fake errcode */
545	jmp early_fault
546
547early_illegal_opcode:
548	movl $6,%edx
549	pushl $0	/* fake errcode */
550	jmp early_fault
551
552early_protection_fault:
553	movl $13,%edx
554	jmp early_fault
555
556early_page_fault:
557	movl $14,%edx
558	jmp early_fault
559
560early_fault:
561	cld
562#ifdef CONFIG_PRINTK
563	pusha
564	movl $(__KERNEL_DS),%eax
565	movl %eax,%ds
566	movl %eax,%es
567	cmpl $2,early_recursion_flag
568	je hlt_loop
569	incl early_recursion_flag
570	movl %cr2,%eax
571	pushl %eax
572	pushl %edx		/* trapno */
573	pushl $fault_msg
574	call printk
575#endif
576	call dump_stack
577hlt_loop:
578	hlt
579	jmp hlt_loop
580
581/* This is the default interrupt "handler" :-) */
582	ALIGN
583ignore_int:
584	cld
585#ifdef CONFIG_PRINTK
586	pushl %eax
587	pushl %ecx
588	pushl %edx
589	pushl %es
590	pushl %ds
591	movl $(__KERNEL_DS),%eax
592	movl %eax,%ds
593	movl %eax,%es
594	cmpl $2,early_recursion_flag
595	je hlt_loop
596	incl early_recursion_flag
597	pushl 16(%esp)
598	pushl 24(%esp)
599	pushl 32(%esp)
600	pushl 40(%esp)
601	pushl $int_msg
602	call printk
603
604	call dump_stack
605
606	addl $(5*4),%esp
607	popl %ds
608	popl %es
609	popl %edx
610	popl %ecx
611	popl %eax
612#endif
613	iret
614
615#include "verify_cpu.S"
616
617	__REFDATA
618.align 4
619ENTRY(initial_code)
620	.long i386_start_kernel
621
622/*
623 * BSS section
624 */
625__PAGE_ALIGNED_BSS
626	.align PAGE_SIZE
627#ifdef CONFIG_X86_PAE
628initial_pg_pmd:
629	.fill 1024*KPMDS,4,0
630#else
631ENTRY(initial_page_table)
632	.fill 1024,4,0
633#endif
634initial_pg_fixmap:
635	.fill 1024,4,0
636ENTRY(empty_zero_page)
637	.fill 4096,1,0
638ENTRY(swapper_pg_dir)
639	.fill 1024,4,0
640
641/*
642 * This starts the data section.
643 */
644#ifdef CONFIG_X86_PAE
645__PAGE_ALIGNED_DATA
646	/* Page-aligned for the benefit of paravirt? */
647	.align PAGE_SIZE
648ENTRY(initial_page_table)
649	.long	pa(initial_pg_pmd+PGD_IDENT_ATTR),0	/* low identity map */
650# if KPMDS == 3
651	.long	pa(initial_pg_pmd+PGD_IDENT_ATTR),0
652	.long	pa(initial_pg_pmd+PGD_IDENT_ATTR+0x1000),0
653	.long	pa(initial_pg_pmd+PGD_IDENT_ATTR+0x2000),0
654# elif KPMDS == 2
655	.long	0,0
656	.long	pa(initial_pg_pmd+PGD_IDENT_ATTR),0
657	.long	pa(initial_pg_pmd+PGD_IDENT_ATTR+0x1000),0
658# elif KPMDS == 1
659	.long	0,0
660	.long	0,0
661	.long	pa(initial_pg_pmd+PGD_IDENT_ATTR),0
662# else
663#  error "Kernel PMDs should be 1, 2 or 3"
664# endif
665	.align PAGE_SIZE		/* needs to be page-sized too */
666#endif
667
668.data
669.balign 4
670ENTRY(stack_start)
671	.long init_thread_union+THREAD_SIZE
672
673early_recursion_flag:
674	.long 0
675
676ready:	.byte 0
677
678int_msg:
679	.asciz "Unknown interrupt or fault at: %p %p %p\n"
680
681fault_msg:
682/* fault info: */
683	.ascii "BUG: Int %d: CR2 %p\n"
684/* pusha regs: */
685	.ascii "     EDI %p  ESI %p  EBP %p  ESP %p\n"
686	.ascii "     EBX %p  EDX %p  ECX %p  EAX %p\n"
687/* fault frame: */
688	.ascii "     err %p  EIP %p   CS %p  flg %p\n"
689	.ascii "Stack: %p %p %p %p %p %p %p %p\n"
690	.ascii "       %p %p %p %p %p %p %p %p\n"
691	.asciz "       %p %p %p %p %p %p %p %p\n"
692
693#include "../../x86/xen/xen-head.S"
694
695/*
696 * The IDT and GDT 'descriptors' are a strange 48-bit object
697 * only used by the lidt and lgdt instructions. They are not
698 * like usual segment descriptors - they consist of a 16-bit
699 * segment size, and 32-bit linear address value:
700 */
701
702.globl boot_gdt_descr
703.globl idt_descr
704
705	ALIGN
706# early boot GDT descriptor (must use 1:1 address mapping)
707	.word 0				# 32 bit align gdt_desc.address
708boot_gdt_descr:
709	.word __BOOT_DS+7
710	.long boot_gdt - __PAGE_OFFSET
711
712	.word 0				# 32-bit align idt_desc.address
713idt_descr:
714	.word IDT_ENTRIES*8-1		# idt contains 256 entries
715	.long idt_table
716
717# boot GDT descriptor (later on used by CPU#0):
718	.word 0				# 32 bit align gdt_desc.address
719ENTRY(early_gdt_descr)
720	.word GDT_ENTRIES*8-1
721	.long gdt_page			/* Overwritten for secondary CPUs */
722
723/*
724 * The boot_gdt must mirror the equivalent in setup.S and is
725 * used only for booting.
726 */
727	.align L1_CACHE_BYTES
728ENTRY(boot_gdt)
729	.fill GDT_ENTRY_BOOT_CS,8,0
730	.quad 0x00cf9a000000ffff	/* kernel 4GB code at 0x00000000 */
731	.quad 0x00cf92000000ffff	/* kernel 4GB data at 0x00000000 */
732