xref: /openbmc/linux/arch/powerpc/kernel/head_44x.S (revision 9ac8d3fb) 
1/*
2 * Kernel execution entry point code.
3 *
4 *    Copyright (c) 1995-1996 Gary Thomas <gdt@linuxppc.org>
5 *      Initial PowerPC version.
6 *    Copyright (c) 1996 Cort Dougan <cort@cs.nmt.edu>
7 *      Rewritten for PReP
8 *    Copyright (c) 1996 Paul Mackerras <paulus@cs.anu.edu.au>
9 *      Low-level exception handers, MMU support, and rewrite.
10 *    Copyright (c) 1997 Dan Malek <dmalek@jlc.net>
11 *      PowerPC 8xx modifications.
12 *    Copyright (c) 1998-1999 TiVo, Inc.
13 *      PowerPC 403GCX modifications.
14 *    Copyright (c) 1999 Grant Erickson <grant@lcse.umn.edu>
15 *      PowerPC 403GCX/405GP modifications.
16 *    Copyright 2000 MontaVista Software Inc.
17 *	PPC405 modifications
18 *      PowerPC 403GCX/405GP modifications.
19 * 	Author: MontaVista Software, Inc.
20 *         	frank_rowand@mvista.com or source@mvista.com
21 * 	   	debbie_chu@mvista.com
22 *    Copyright 2002-2005 MontaVista Software, Inc.
23 *      PowerPC 44x support, Matt Porter <mporter@kernel.crashing.org>
24 *
25 * This program is free software; you can redistribute  it and/or modify it
26 * under  the terms of  the GNU General  Public License as published by the
27 * Free Software Foundation;  either version 2 of the  License, or (at your
28 * option) any later version.
29 */
30
31#include <asm/processor.h>
32#include <asm/page.h>
33#include <asm/mmu.h>
34#include <asm/pgtable.h>
35#include <asm/cputable.h>
36#include <asm/thread_info.h>
37#include <asm/ppc_asm.h>
38#include <asm/asm-offsets.h>
39#include "head_booke.h"
40
41
42/* As with the other PowerPC ports, it is expected that when code
43 * execution begins here, the following registers contain valid, yet
44 * optional, information:
45 *
46 *   r3 - Board info structure pointer (DRAM, frequency, MAC address, etc.)
47 *   r4 - Starting address of the init RAM disk
48 *   r5 - Ending address of the init RAM disk
49 *   r6 - Start of kernel command line string (e.g. "mem=128")
50 *   r7 - End of kernel command line string
51 *
52 */
53	.section	.text.head, "ax"
54_ENTRY(_stext);
55_ENTRY(_start);
56	/*
57	 * Reserve a word at a fixed location to store the address
58	 * of abatron_pteptrs
59	 */
60	nop
61/*
62 * Save parameters we are passed
63 */
64	mr	r31,r3
65	mr	r30,r4
66	mr	r29,r5
67	mr	r28,r6
68	mr	r27,r7
69	li	r24,0		/* CPU number */
70
71/*
72 * Set up the initial MMU state
73 *
74 * We are still executing code at the virtual address
75 * mappings set by the firmware for the base of RAM.
76 *
77 * We first invalidate all TLB entries but the one
78 * we are running from.  We then load the KERNELBASE
79 * mappings so we can begin to use kernel addresses
80 * natively and so the interrupt vector locations are
81 * permanently pinned (necessary since Book E
82 * implementations always have translation enabled).
83 *
84 * TODO: Use the known TLB entry we are running from to
85 *	 determine which physical region we are located
86 *	 in.  This can be used to determine where in RAM
87 *	 (on a shared CPU system) or PCI memory space
88 *	 (on a DRAMless system) we are located.
89 *       For now, we assume a perfect world which means
90 *	 we are located at the base of DRAM (physical 0).
91 */
92
93/*
94 * Search TLB for entry that we are currently using.
95 * Invalidate all entries but the one we are using.
96 */
97	/* Load our current PID->MMUCR TID and MSR IS->MMUCR STS */
98	mfspr	r3,SPRN_PID			/* Get PID */
99	mfmsr	r4				/* Get MSR */
100	andi.	r4,r4,MSR_IS@l			/* TS=1? */
101	beq	wmmucr				/* If not, leave STS=0 */
102	oris	r3,r3,PPC44x_MMUCR_STS@h	/* Set STS=1 */
103wmmucr:	mtspr	SPRN_MMUCR,r3			/* Put MMUCR */
104	sync
105
106	bl	invstr				/* Find our address */
107invstr:	mflr	r5				/* Make it accessible */
108	tlbsx	r23,0,r5			/* Find entry we are in */
109	li	r4,0				/* Start at TLB entry 0 */
110	li	r3,0				/* Set PAGEID inval value */
1111:	cmpw	r23,r4				/* Is this our entry? */
112	beq	skpinv				/* If so, skip the inval */
113	tlbwe	r3,r4,PPC44x_TLB_PAGEID		/* If not, inval the entry */
114skpinv:	addi	r4,r4,1				/* Increment */
115	cmpwi	r4,64				/* Are we done? */
116	bne	1b				/* If not, repeat */
117	isync					/* If so, context change */
118
119/*
120 * Configure and load pinned entry into TLB slot 63.
121 */
122
123	lis	r3,PAGE_OFFSET@h
124	ori	r3,r3,PAGE_OFFSET@l
125
126	/* Kernel is at the base of RAM */
127	li r4, 0			/* Load the kernel physical address */
128
129	/* Load the kernel PID = 0 */
130	li	r0,0
131	mtspr	SPRN_PID,r0
132	sync
133
134	/* Initialize MMUCR */
135	li	r5,0
136	mtspr	SPRN_MMUCR,r5
137	sync
138
139 	/* pageid fields */
140	clrrwi	r3,r3,10		/* Mask off the effective page number */
141	ori	r3,r3,PPC44x_TLB_VALID | PPC44x_TLB_256M
142
143	/* xlat fields */
144	clrrwi	r4,r4,10		/* Mask off the real page number */
145					/* ERPN is 0 for first 4GB page */
146
147	/* attrib fields */
148	/* Added guarded bit to protect against speculative loads/stores */
149	li	r5,0
150	ori	r5,r5,(PPC44x_TLB_SW | PPC44x_TLB_SR | PPC44x_TLB_SX | PPC44x_TLB_G)
151
152        li      r0,63                    /* TLB slot 63 */
153
154	tlbwe	r3,r0,PPC44x_TLB_PAGEID	/* Load the pageid fields */
155	tlbwe	r4,r0,PPC44x_TLB_XLAT	/* Load the translation fields */
156	tlbwe	r5,r0,PPC44x_TLB_ATTRIB	/* Load the attrib/access fields */
157
158	/* Force context change */
159	mfmsr	r0
160	mtspr	SPRN_SRR1, r0
161	lis	r0,3f@h
162	ori	r0,r0,3f@l
163	mtspr	SPRN_SRR0,r0
164	sync
165	rfi
166
167	/* If necessary, invalidate original entry we used */
1683:	cmpwi	r23,63
169	beq	4f
170	li	r6,0
171	tlbwe   r6,r23,PPC44x_TLB_PAGEID
172	isync
173
1744:
175#ifdef CONFIG_PPC_EARLY_DEBUG_44x
176	/* Add UART mapping for early debug. */
177
178 	/* pageid fields */
179	lis	r3,PPC44x_EARLY_DEBUG_VIRTADDR@h
180	ori	r3,r3,PPC44x_TLB_VALID|PPC44x_TLB_TS|PPC44x_TLB_64K
181
182	/* xlat fields */
183	lis	r4,CONFIG_PPC_EARLY_DEBUG_44x_PHYSLOW@h
184	ori	r4,r4,CONFIG_PPC_EARLY_DEBUG_44x_PHYSHIGH
185
186	/* attrib fields */
187	li	r5,(PPC44x_TLB_SW|PPC44x_TLB_SR|PPC44x_TLB_I|PPC44x_TLB_G)
188        li      r0,62                    /* TLB slot 0 */
189
190	tlbwe	r3,r0,PPC44x_TLB_PAGEID
191	tlbwe	r4,r0,PPC44x_TLB_XLAT
192	tlbwe	r5,r0,PPC44x_TLB_ATTRIB
193
194	/* Force context change */
195	isync
196#endif /* CONFIG_PPC_EARLY_DEBUG_44x */
197
198	/* Establish the interrupt vector offsets */
199	SET_IVOR(0,  CriticalInput);
200	SET_IVOR(1,  MachineCheck);
201	SET_IVOR(2,  DataStorage);
202	SET_IVOR(3,  InstructionStorage);
203	SET_IVOR(4,  ExternalInput);
204	SET_IVOR(5,  Alignment);
205	SET_IVOR(6,  Program);
206	SET_IVOR(7,  FloatingPointUnavailable);
207	SET_IVOR(8,  SystemCall);
208	SET_IVOR(9,  AuxillaryProcessorUnavailable);
209	SET_IVOR(10, Decrementer);
210	SET_IVOR(11, FixedIntervalTimer);
211	SET_IVOR(12, WatchdogTimer);
212	SET_IVOR(13, DataTLBError);
213	SET_IVOR(14, InstructionTLBError);
214	SET_IVOR(15, DebugCrit);
215
216	/* Establish the interrupt vector base */
217	lis	r4,interrupt_base@h	/* IVPR only uses the high 16-bits */
218	mtspr	SPRN_IVPR,r4
219
220	/*
221	 * This is where the main kernel code starts.
222	 */
223
224	/* ptr to current */
225	lis	r2,init_task@h
226	ori	r2,r2,init_task@l
227
228	/* ptr to current thread */
229	addi	r4,r2,THREAD	/* init task's THREAD */
230	mtspr	SPRN_SPRG3,r4
231
232	/* stack */
233	lis	r1,init_thread_union@h
234	ori	r1,r1,init_thread_union@l
235	li	r0,0
236	stwu	r0,THREAD_SIZE-STACK_FRAME_OVERHEAD(r1)
237
238	bl	early_init
239
240/*
241 * Decide what sort of machine this is and initialize the MMU.
242 */
243	mr	r3,r31
244	mr	r4,r30
245	mr	r5,r29
246	mr	r6,r28
247	mr	r7,r27
248	bl	machine_init
249	bl	MMU_init
250
251	/* Setup PTE pointers for the Abatron bdiGDB */
252	lis	r6, swapper_pg_dir@h
253	ori	r6, r6, swapper_pg_dir@l
254	lis	r5, abatron_pteptrs@h
255	ori	r5, r5, abatron_pteptrs@l
256	lis	r4, KERNELBASE@h
257	ori	r4, r4, KERNELBASE@l
258	stw	r5, 0(r4)	/* Save abatron_pteptrs at a fixed location */
259	stw	r6, 0(r5)
260
261	/* Let's move on */
262	lis	r4,start_kernel@h
263	ori	r4,r4,start_kernel@l
264	lis	r3,MSR_KERNEL@h
265	ori	r3,r3,MSR_KERNEL@l
266	mtspr	SPRN_SRR0,r4
267	mtspr	SPRN_SRR1,r3
268	rfi			/* change context and jump to start_kernel */
269
270/*
271 * Interrupt vector entry code
272 *
273 * The Book E MMUs are always on so we don't need to handle
274 * interrupts in real mode as with previous PPC processors. In
275 * this case we handle interrupts in the kernel virtual address
276 * space.
277 *
278 * Interrupt vectors are dynamically placed relative to the
279 * interrupt prefix as determined by the address of interrupt_base.
280 * The interrupt vectors offsets are programmed using the labels
281 * for each interrupt vector entry.
282 *
283 * Interrupt vectors must be aligned on a 16 byte boundary.
284 * We align on a 32 byte cache line boundary for good measure.
285 */
286
287interrupt_base:
288	/* Critical Input Interrupt */
289	CRITICAL_EXCEPTION(0x0100, CriticalInput, unknown_exception)
290
291	/* Machine Check Interrupt */
292	CRITICAL_EXCEPTION(0x0200, MachineCheck, machine_check_exception)
293	MCHECK_EXCEPTION(0x0210, MachineCheckA, machine_check_exception)
294
295	/* Data Storage Interrupt */
296	DATA_STORAGE_EXCEPTION
297
298		/* Instruction Storage Interrupt */
299	INSTRUCTION_STORAGE_EXCEPTION
300
301	/* External Input Interrupt */
302	EXCEPTION(0x0500, ExternalInput, do_IRQ, EXC_XFER_LITE)
303
304	/* Alignment Interrupt */
305	ALIGNMENT_EXCEPTION
306
307	/* Program Interrupt */
308	PROGRAM_EXCEPTION
309
310	/* Floating Point Unavailable Interrupt */
311#ifdef CONFIG_PPC_FPU
312	FP_UNAVAILABLE_EXCEPTION
313#else
314	EXCEPTION(0x2010, FloatingPointUnavailable, unknown_exception, EXC_XFER_EE)
315#endif
316	/* System Call Interrupt */
317	START_EXCEPTION(SystemCall)
318	NORMAL_EXCEPTION_PROLOG
319	EXC_XFER_EE_LITE(0x0c00, DoSyscall)
320
321	/* Auxillary Processor Unavailable Interrupt */
322	EXCEPTION(0x2020, AuxillaryProcessorUnavailable, unknown_exception, EXC_XFER_EE)
323
324	/* Decrementer Interrupt */
325	DECREMENTER_EXCEPTION
326
327	/* Fixed Internal Timer Interrupt */
328	/* TODO: Add FIT support */
329	EXCEPTION(0x1010, FixedIntervalTimer, unknown_exception, EXC_XFER_EE)
330
331	/* Watchdog Timer Interrupt */
332	/* TODO: Add watchdog support */
333#ifdef CONFIG_BOOKE_WDT
334	CRITICAL_EXCEPTION(0x1020, WatchdogTimer, WatchdogException)
335#else
336	CRITICAL_EXCEPTION(0x1020, WatchdogTimer, unknown_exception)
337#endif
338
339	/* Data TLB Error Interrupt */
340	START_EXCEPTION(DataTLBError)
341	mtspr	SPRN_SPRG0, r10		/* Save some working registers */
342	mtspr	SPRN_SPRG1, r11
343	mtspr	SPRN_SPRG4W, r12
344	mtspr	SPRN_SPRG5W, r13
345	mfcr	r11
346	mtspr	SPRN_SPRG7W, r11
347	mfspr	r10, SPRN_DEAR		/* Get faulting address */
348
349	/* If we are faulting a kernel address, we have to use the
350	 * kernel page tables.
351	 */
352	lis	r11, PAGE_OFFSET@h
353	cmplw	r10, r11
354	blt+	3f
355	lis	r11, swapper_pg_dir@h
356	ori	r11, r11, swapper_pg_dir@l
357
358	mfspr	r12,SPRN_MMUCR
359	rlwinm	r12,r12,0,0,23		/* Clear TID */
360
361	b	4f
362
363	/* Get the PGD for the current thread */
3643:
365	mfspr	r11,SPRN_SPRG3
366	lwz	r11,PGDIR(r11)
367
368	/* Load PID into MMUCR TID */
369	mfspr	r12,SPRN_MMUCR
370	mfspr   r13,SPRN_PID		/* Get PID */
371	rlwimi	r12,r13,0,24,31		/* Set TID */
372
3734:
374	mtspr	SPRN_MMUCR,r12
375
376	/* Mask of required permission bits. Note that while we
377	 * do copy ESR:ST to _PAGE_RW position as trying to write
378	 * to an RO page is pretty common, we don't do it with
379	 * _PAGE_DIRTY. We could do it, but it's a fairly rare
380	 * event so I'd rather take the overhead when it happens
381	 * rather than adding an instruction here. We should measure
382	 * whether the whole thing is worth it in the first place
383	 * as we could avoid loading SPRN_ESR completely in the first
384	 * place...
385	 *
386	 * TODO: Is it worth doing that mfspr & rlwimi in the first
387	 *       place or can we save a couple of instructions here ?
388	 */
389	mfspr	r12,SPRN_ESR
390	li	r13,_PAGE_PRESENT|_PAGE_ACCESSED
391	rlwimi	r13,r12,10,30,30
392
393	/* Load the PTE */
394	rlwinm 	r12, r10, 13, 19, 29	/* Compute pgdir/pmd offset */
395	lwzx	r11, r12, r11		/* Get pgd/pmd entry */
396	rlwinm.	r12, r11, 0, 0, 20	/* Extract pt base address */
397	beq	2f			/* Bail if no table */
398
399	rlwimi	r12, r10, 23, 20, 28	/* Compute pte address */
400	lwz	r11, 0(r12)		/* Get high word of pte entry */
401	lwz	r12, 4(r12)		/* Get low word of pte entry */
402
403	lis	r10,tlb_44x_index@ha
404
405	andc.	r13,r13,r12		/* Check permission */
406
407	/* Load the next available TLB index */
408	lwz	r13,tlb_44x_index@l(r10)
409
410	bne	2f			/* Bail if permission mismach */
411
412	/* Increment, rollover, and store TLB index */
413	addi	r13,r13,1
414
415	/* Compare with watermark (instruction gets patched) */
416	.globl tlb_44x_patch_hwater_D
417tlb_44x_patch_hwater_D:
418	cmpwi	0,r13,1			/* reserve entries */
419	ble	5f
420	li	r13,0
4215:
422	/* Store the next available TLB index */
423	stw	r13,tlb_44x_index@l(r10)
424
425	/* Re-load the faulting address */
426	mfspr	r10,SPRN_DEAR
427
428	 /* Jump to common tlb load */
429	b	finish_tlb_load
430
4312:
432	/* The bailout.  Restore registers to pre-exception conditions
433	 * and call the heavyweights to help us out.
434	 */
435	mfspr	r11, SPRN_SPRG7R
436	mtcr	r11
437	mfspr	r13, SPRN_SPRG5R
438	mfspr	r12, SPRN_SPRG4R
439	mfspr	r11, SPRN_SPRG1
440	mfspr	r10, SPRN_SPRG0
441	b	DataStorage
442
443	/* Instruction TLB Error Interrupt */
444	/*
445	 * Nearly the same as above, except we get our
446	 * information from different registers and bailout
447	 * to a different point.
448	 */
449	START_EXCEPTION(InstructionTLBError)
450	mtspr	SPRN_SPRG0, r10		/* Save some working registers */
451	mtspr	SPRN_SPRG1, r11
452	mtspr	SPRN_SPRG4W, r12
453	mtspr	SPRN_SPRG5W, r13
454	mfcr	r11
455	mtspr	SPRN_SPRG7W, r11
456	mfspr	r10, SPRN_SRR0		/* Get faulting address */
457
458	/* If we are faulting a kernel address, we have to use the
459	 * kernel page tables.
460	 */
461	lis	r11, PAGE_OFFSET@h
462	cmplw	r10, r11
463	blt+	3f
464	lis	r11, swapper_pg_dir@h
465	ori	r11, r11, swapper_pg_dir@l
466
467	mfspr	r12,SPRN_MMUCR
468	rlwinm	r12,r12,0,0,23		/* Clear TID */
469
470	b	4f
471
472	/* Get the PGD for the current thread */
4733:
474	mfspr	r11,SPRN_SPRG3
475	lwz	r11,PGDIR(r11)
476
477	/* Load PID into MMUCR TID */
478	mfspr	r12,SPRN_MMUCR
479	mfspr   r13,SPRN_PID		/* Get PID */
480	rlwimi	r12,r13,0,24,31		/* Set TID */
481
4824:
483	mtspr	SPRN_MMUCR,r12
484
485	/* Make up the required permissions */
486	li	r13,_PAGE_PRESENT | _PAGE_ACCESSED | _PAGE_HWEXEC
487
488	rlwinm	r12, r10, 13, 19, 29	/* Compute pgdir/pmd offset */
489	lwzx	r11, r12, r11		/* Get pgd/pmd entry */
490	rlwinm.	r12, r11, 0, 0, 20	/* Extract pt base address */
491	beq	2f			/* Bail if no table */
492
493	rlwimi	r12, r10, 23, 20, 28	/* Compute pte address */
494	lwz	r11, 0(r12)		/* Get high word of pte entry */
495	lwz	r12, 4(r12)		/* Get low word of pte entry */
496
497	lis	r10,tlb_44x_index@ha
498
499	andc.	r13,r13,r12		/* Check permission */
500
501	/* Load the next available TLB index */
502	lwz	r13,tlb_44x_index@l(r10)
503
504	bne	2f			/* Bail if permission mismach */
505
506	/* Increment, rollover, and store TLB index */
507	addi	r13,r13,1
508
509	/* Compare with watermark (instruction gets patched) */
510	.globl tlb_44x_patch_hwater_I
511tlb_44x_patch_hwater_I:
512	cmpwi	0,r13,1			/* reserve entries */
513	ble	5f
514	li	r13,0
5155:
516	/* Store the next available TLB index */
517	stw	r13,tlb_44x_index@l(r10)
518
519	/* Re-load the faulting address */
520	mfspr	r10,SPRN_SRR0
521
522	/* Jump to common TLB load point */
523	b	finish_tlb_load
524
5252:
526	/* The bailout.  Restore registers to pre-exception conditions
527	 * and call the heavyweights to help us out.
528	 */
529	mfspr	r11, SPRN_SPRG7R
530	mtcr	r11
531	mfspr	r13, SPRN_SPRG5R
532	mfspr	r12, SPRN_SPRG4R
533	mfspr	r11, SPRN_SPRG1
534	mfspr	r10, SPRN_SPRG0
535	b	InstructionStorage
536
537	/* Debug Interrupt */
538	DEBUG_CRIT_EXCEPTION
539
540/*
541 * Local functions
542  */
543
544/*
545
546 * Both the instruction and data TLB miss get to this
547 * point to load the TLB.
548 * 	r10 - EA of fault
549 * 	r11 - PTE high word value
550 *	r12 - PTE low word value
551 *	r13 - TLB index
552 *	MMUCR - loaded with proper value when we get here
553 *	Upon exit, we reload everything and RFI.
554 */
555finish_tlb_load:
556	/* Combine RPN & ERPN an write WS 0 */
557	rlwimi	r11,r12,0,0,19
558	tlbwe	r11,r13,PPC44x_TLB_XLAT
559
560	/*
561	 * Create WS1. This is the faulting address (EPN),
562	 * page size, and valid flag.
563	 */
564	li	r11,PPC44x_TLB_VALID | PPC44x_TLB_4K
565	rlwimi	r10,r11,0,20,31			/* Insert valid and page size*/
566	tlbwe	r10,r13,PPC44x_TLB_PAGEID	/* Write PAGEID */
567
568	/* And WS 2 */
569	li	r10,0xf85			/* Mask to apply from PTE */
570	rlwimi	r10,r12,29,30,30		/* DIRTY -> SW position */
571	and	r11,r12,r10			/* Mask PTE bits to keep */
572	andi.	r10,r12,_PAGE_USER		/* User page ? */
573	beq	1f				/* nope, leave U bits empty */
574	rlwimi	r11,r11,3,26,28			/* yes, copy S bits to U */
5751:	tlbwe	r11,r13,PPC44x_TLB_ATTRIB	/* Write ATTRIB */
576
577	/* Done...restore registers and get out of here.
578	*/
579	mfspr	r11, SPRN_SPRG7R
580	mtcr	r11
581	mfspr	r13, SPRN_SPRG5R
582	mfspr	r12, SPRN_SPRG4R
583	mfspr	r11, SPRN_SPRG1
584	mfspr	r10, SPRN_SPRG0
585	rfi					/* Force context change */
586
587/*
588 * Global functions
589 */
590
591/*
592 * Adjust the machine check IVOR on 440A cores
593 */
594_GLOBAL(__fixup_440A_mcheck)
595	li	r3,MachineCheckA@l
596	mtspr	SPRN_IVOR1,r3
597	sync
598	blr
599
600/*
601 * extern void giveup_altivec(struct task_struct *prev)
602 *
603 * The 44x core does not have an AltiVec unit.
604 */
605_GLOBAL(giveup_altivec)
606	blr
607
608/*
609 * extern void giveup_fpu(struct task_struct *prev)
610 *
611 * The 44x core does not have an FPU.
612 */
613#ifndef CONFIG_PPC_FPU
614_GLOBAL(giveup_fpu)
615	blr
616#endif
617
618_GLOBAL(set_context)
619
620#ifdef CONFIG_BDI_SWITCH
621	/* Context switch the PTE pointer for the Abatron BDI2000.
622	 * The PGDIR is the second parameter.
623	 */
624	lis	r5, abatron_pteptrs@h
625	ori	r5, r5, abatron_pteptrs@l
626	stw	r4, 0x4(r5)
627#endif
628	mtspr	SPRN_PID,r3
629	isync			/* Force context change */
630	blr
631
632/*
633 * We put a few things here that have to be page-aligned. This stuff
634 * goes at the beginning of the data segment, which is page-aligned.
635 */
636	.data
637	.align	12
638	.globl	sdata
639sdata:
640	.globl	empty_zero_page
641empty_zero_page:
642	.space	4096
643
644/*
645 * To support >32-bit physical addresses, we use an 8KB pgdir.
646 */
647	.globl	swapper_pg_dir
648swapper_pg_dir:
649	.space	PGD_TABLE_SIZE
650
651/*
652 * Room for two PTE pointers, usually the kernel and current user pointers
653 * to their respective root page table.
654 */
655abatron_pteptrs:
656	.space	8
657