xref: /openbmc/linux/arch/xtensa/kernel/align.S (revision 95e9fd10) 
1/*
2 * arch/xtensa/kernel/align.S
3 *
4 * Handle unalignment exceptions in kernel space.
5 *
6 * This file is subject to the terms and conditions of the GNU General
7 * Public License.  See the file "COPYING" in the main directory of
8 * this archive for more details.
9 *
10 * Copyright (C) 2001 - 2005 Tensilica, Inc.
11 *
12 * Rewritten by Chris Zankel <chris@zankel.net>
13 *
14 * Based on work from Joe Taylor <joe@tensilica.com, joetylr@yahoo.com>
15 * and Marc Gauthier <marc@tensilica.com, marc@alimni.uwaterloo.ca>
16 */
17
18#include <linux/linkage.h>
19#include <asm/current.h>
20#include <asm/asm-offsets.h>
21#include <asm/processor.h>
22
23#if XCHAL_UNALIGNED_LOAD_EXCEPTION || XCHAL_UNALIGNED_STORE_EXCEPTION
24
25/*  First-level exception handler for unaligned exceptions.
26 *
27 *  Note: This handler works only for kernel exceptions.  Unaligned user
28 *        access should get a seg fault.
29 */
30
31/* Big and little endian 16-bit values are located in
32 * different halves of a register.  HWORD_START helps to
33 * abstract the notion of extracting a 16-bit value from a
34 * register.
35 * We also have to define new shifting instructions because
36 * lsb and msb are on 'opposite' ends in a register for
37 * different endian machines.
38 *
39 * Assume a memory region in ascending address:
40 *   	0 1 2 3|4 5 6 7
41 *
42 * When loading one word into a register, the content of that register is:
43 *  LE	3 2 1 0, 7 6 5 4
44 *  BE  0 1 2 3, 4 5 6 7
45 *
46 * Masking the bits of the higher/lower address means:
47 *  LE  X X 0 0, 0 0 X X
48 *  BE	0 0 X X, X X 0 0
49 *
50 * Shifting to higher/lower addresses, means:
51 *  LE  shift left / shift right
52 *  BE  shift right / shift left
53 *
54 * Extracting 16 bits from a 32 bit reg. value to higher/lower address means:
55 *  LE  mask 0 0 X X / shift left
56 *  BE  shift left / mask 0 0 X X
57 */
58
59#define UNALIGNED_USER_EXCEPTION
60
61#if XCHAL_HAVE_BE
62
63#define HWORD_START	16
64#define	INSN_OP0	28
65#define	INSN_T		24
66#define	INSN_OP1	16
67
68.macro __src_b	r, w0, w1;	src	\r, \w0, \w1;	.endm
69.macro __ssa8	r;		ssa8b	\r;		.endm
70.macro __ssa8r	r;		ssa8l	\r;		.endm
71.macro __sh	r, s;		srl	\r, \s;		.endm
72.macro __sl	r, s;		sll	\r, \s;		.endm
73.macro __exth	r, s;		extui	\r, \s, 0, 16;	.endm
74.macro __extl	r, s;		slli	\r, \s, 16;	.endm
75
76#else
77
78#define HWORD_START	0
79#define	INSN_OP0	0
80#define	INSN_T		4
81#define	INSN_OP1	12
82
83.macro __src_b	r, w0, w1;	src	\r, \w1, \w0;	.endm
84.macro __ssa8	r;		ssa8l	\r;		.endm
85.macro __ssa8r	r;		ssa8b	\r;		.endm
86.macro __sh	r, s;		sll	\r, \s;		.endm
87.macro __sl	r, s;		srl	\r, \s;		.endm
88.macro __exth	r, s;		slli	\r, \s, 16;	.endm
89.macro __extl	r, s;		extui	\r, \s, 0, 16;	.endm
90
91#endif
92
93/*
94 *	xxxx xxxx = imm8 field
95 *	     yyyy = imm4 field
96 *	     ssss = s field
97 *	     tttt = t field
98 *
99 *	       		 16		    0
100 *		          -------------------
101 *	L32I.N		  yyyy ssss tttt 1000
102 *	S32I.N	          yyyy ssss tttt 1001
103 *
104 *	       23			    0
105 *		-----------------------------
106 *	res	          0000           0010
107 *	L16UI	xxxx xxxx 0001 ssss tttt 0010
108 *	L32I	xxxx xxxx 0010 ssss tttt 0010
109 *	XXX	          0011 ssss tttt 0010
110 *	XXX	          0100 ssss tttt 0010
111 *	S16I	xxxx xxxx 0101 ssss tttt 0010
112 *	S32I	xxxx xxxx 0110 ssss tttt 0010
113 *	XXX	          0111 ssss tttt 0010
114 *	XXX	          1000 ssss tttt 0010
115 *	L16SI	xxxx xxxx 1001 ssss tttt 0010
116 *	XXX	          1010           0010
117 *      **L32AI	xxxx xxxx 1011 ssss tttt 0010 unsupported
118 *	XXX	          1100           0010
119 *	XXX	          1101           0010
120 *	XXX	          1110           0010
121 *	**S32RI	xxxx xxxx 1111 ssss tttt 0010 unsupported
122 *		-----------------------------
123 *                           ^         ^    ^
124 *    sub-opcode (NIBBLE_R) -+         |    |
125 *       t field (NIBBLE_T) -----------+    |
126 *  major opcode (NIBBLE_OP0) --------------+
127 */
128
129#define OP0_L32I_N	0x8		/* load immediate narrow */
130#define OP0_S32I_N	0x9		/* store immediate narrow */
131#define OP1_SI_MASK	0x4		/* OP1 bit set for stores */
132#define OP1_SI_BIT	2		/* OP1 bit number for stores */
133
134#define OP1_L32I	0x2
135#define OP1_L16UI	0x1
136#define OP1_L16SI	0x9
137#define OP1_L32AI	0xb
138
139#define OP1_S32I	0x6
140#define OP1_S16I	0x5
141#define OP1_S32RI	0xf
142
143/*
144 * Entry condition:
145 *
146 *   a0:	trashed, original value saved on stack (PT_AREG0)
147 *   a1:	a1
148 *   a2:	new stack pointer, original in DEPC
149 *   a3:	dispatch table
150 *   depc:	a2, original value saved on stack (PT_DEPC)
151 *   excsave_1:	a3
152 *
153 *   PT_DEPC >= VALID_DOUBLE_EXCEPTION_ADDRESS: double exception, DEPC
154 *	     <  VALID_DOUBLE_EXCEPTION_ADDRESS: regular exception
155 */
156
157
158ENTRY(fast_unaligned)
159
160	/* Note: We don't expect the address to be aligned on a word
161	 *       boundary. After all, the processor generated that exception
162	 *       and it would be a hardware fault.
163	 */
164
165	/* Save some working register */
166
167	s32i	a4, a2, PT_AREG4
168	s32i	a5, a2, PT_AREG5
169	s32i	a6, a2, PT_AREG6
170	s32i	a7, a2, PT_AREG7
171	s32i	a8, a2, PT_AREG8
172
173	rsr	a0, DEPC
174	xsr	a3, EXCSAVE_1
175	s32i	a0, a2, PT_AREG2
176	s32i	a3, a2, PT_AREG3
177
178	/* Keep value of SAR in a0 */
179
180	rsr	a0, SAR
181	rsr	a8, EXCVADDR		# load unaligned memory address
182
183	/* Now, identify one of the following load/store instructions.
184	 *
185	 * The only possible danger of a double exception on the
186	 * following l32i instructions is kernel code in vmalloc
187	 * memory. The processor was just executing at the EPC_1
188	 * address, and indeed, already fetched the instruction.  That
189	 * guarantees a TLB mapping, which hasn't been replaced by
190	 * this unaligned exception handler that uses only static TLB
191	 * mappings. However, high-level interrupt handlers might
192	 * modify TLB entries, so for the generic case, we register a
193	 * TABLE_FIXUP handler here, too.
194	 */
195
196	/* a3...a6 saved on stack, a2 = SP */
197
198	/* Extract the instruction that caused the unaligned access. */
199
200	rsr	a7, EPC_1	# load exception address
201	movi	a3, ~3
202	and	a3, a3, a7	# mask lower bits
203
204	l32i	a4, a3, 0	# load 2 words
205	l32i	a5, a3, 4
206
207	__ssa8	a7
208	__src_b	a4, a4, a5	# a4 has the instruction
209
210	/* Analyze the instruction (load or store?). */
211
212	extui	a5, a4, INSN_OP0, 4	# get insn.op0 nibble
213
214#if XCHAL_HAVE_DENSITY
215	_beqi	a5, OP0_L32I_N, .Lload	# L32I.N, jump
216	addi	a6, a5, -OP0_S32I_N
217	_beqz	a6, .Lstore		# S32I.N, do a store
218#endif
219	/* 'store indicator bit' not set, jump */
220	_bbci.l	a4, OP1_SI_BIT + INSN_OP1, .Lload
221
222	/* Store: Jump to table entry to get the value in the source register.*/
223
224.Lstore:movi	a5, .Lstore_table	# table
225	extui	a6, a4, INSN_T, 4	# get source register
226	addx8	a5, a6, a5
227	jx	a5			# jump into table
228
229	/* Invalid instruction, CRITICAL! */
230.Linvalid_instruction_load:
231	j	.Linvalid_instruction
232
233	/* Load: Load memory address. */
234
235.Lload: movi	a3, ~3
236	and	a3, a3, a8		# align memory address
237
238	__ssa8	a8
239#ifdef UNALIGNED_USER_EXCEPTION
240	addi	a3, a3, 8
241	l32e	a5, a3, -8
242	l32e	a6, a3, -4
243#else
244	l32i	a5, a3, 0
245	l32i	a6, a3, 4
246#endif
247	__src_b	a3, a5, a6		# a3 has the data word
248
249#if XCHAL_HAVE_DENSITY
250	addi	a7, a7, 2		# increment PC (assume 16-bit insn)
251
252	extui	a5, a4, INSN_OP0, 4
253	_beqi	a5, OP0_L32I_N, 1f	# l32i.n: jump
254
255	addi	a7, a7, 1
256#else
257	addi	a7, a7, 3
258#endif
259
260	extui	a5, a4, INSN_OP1, 4
261	_beqi	a5, OP1_L32I, 1f	# l32i: jump
262
263	extui	a3, a3, 0, 16		# extract lower 16 bits
264	_beqi	a5, OP1_L16UI, 1f
265	addi	a5, a5, -OP1_L16SI
266	_bnez	a5, .Linvalid_instruction_load
267
268	/* sign extend value */
269
270	slli	a3, a3, 16
271	srai	a3, a3, 16
272
273	/* Set target register. */
274
2751:
276
277#if XCHAL_HAVE_LOOPS
278	rsr	a5, LEND		# check if we reached LEND
279	bne	a7, a5, 1f
280	rsr	a5, LCOUNT		# and LCOUNT != 0
281	beqz	a5, 1f
282	addi	a5, a5, -1		# decrement LCOUNT and set
283	rsr	a7, LBEG		# set PC to LBEGIN
284	wsr	a5, LCOUNT
285#endif
286
2871:	wsr	a7, EPC_1		# skip load instruction
288	extui	a4, a4, INSN_T, 4	# extract target register
289	movi	a5, .Lload_table
290	addx8	a4, a4, a5
291	jx	a4			# jump to entry for target register
292
293	.align	8
294.Lload_table:
295	s32i	a3, a2, PT_AREG0;	_j .Lexit;	.align 8
296	mov	a1, a3;			_j .Lexit;	.align 8 # fishy??
297	s32i	a3, a2, PT_AREG2;	_j .Lexit;	.align 8
298	s32i	a3, a2, PT_AREG3;	_j .Lexit;	.align 8
299	s32i	a3, a2, PT_AREG4;	_j .Lexit;	.align 8
300	s32i	a3, a2, PT_AREG5;	_j .Lexit;	.align 8
301	s32i	a3, a2, PT_AREG6;	_j .Lexit;	.align 8
302	s32i	a3, a2, PT_AREG7;	_j .Lexit;	.align 8
303	s32i	a3, a2, PT_AREG8;	_j .Lexit;	.align 8
304	mov	a9, a3		;	_j .Lexit;	.align 8
305	mov	a10, a3		;	_j .Lexit;	.align 8
306	mov	a11, a3		;	_j .Lexit;	.align 8
307	mov	a12, a3		;	_j .Lexit;	.align 8
308	mov	a13, a3		;	_j .Lexit;	.align 8
309	mov	a14, a3		;	_j .Lexit;	.align 8
310	mov	a15, a3		;	_j .Lexit;	.align 8
311
312.Lstore_table:
313	l32i	a3, a2, PT_AREG0;	_j 1f;	.align 8
314	mov	a3, a1;			_j 1f;	.align 8	# fishy??
315	l32i	a3, a2, PT_AREG2;	_j 1f;	.align 8
316	l32i	a3, a2, PT_AREG3;	_j 1f;	.align 8
317	l32i	a3, a2, PT_AREG4;	_j 1f;	.align 8
318	l32i	a3, a2, PT_AREG5;	_j 1f;	.align 8
319	l32i	a3, a2, PT_AREG6;	_j 1f;	.align 8
320	l32i	a3, a2, PT_AREG7;	_j 1f;	.align 8
321	l32i	a3, a2, PT_AREG8;	_j 1f;	.align 8
322	mov	a3, a9		;	_j 1f;	.align 8
323	mov	a3, a10		;	_j 1f;	.align 8
324	mov	a3, a11		;	_j 1f;	.align 8
325	mov	a3, a12		;	_j 1f;	.align 8
326	mov	a3, a13		;	_j 1f;	.align 8
327	mov	a3, a14		;	_j 1f;	.align 8
328	mov	a3, a15		;	_j 1f;	.align 8
329
3301: 	# a7: instruction pointer, a4: instruction, a3: value
331
332	movi	a6, 0			# mask: ffffffff:00000000
333
334#if XCHAL_HAVE_DENSITY
335	addi	a7, a7, 2		# incr. PC,assume 16-bit instruction
336
337	extui	a5, a4, INSN_OP0, 4	# extract OP0
338	addi	a5, a5, -OP0_S32I_N
339	_beqz	a5, 1f			# s32i.n: jump
340
341	addi	a7, a7, 1		# increment PC, 32-bit instruction
342#else
343	addi	a7, a7, 3		# increment PC, 32-bit instruction
344#endif
345
346	extui	a5, a4, INSN_OP1, 4	# extract OP1
347	_beqi	a5, OP1_S32I, 1f	# jump if 32 bit store
348	_bnei	a5, OP1_S16I, .Linvalid_instruction_store
349
350	movi	a5, -1
351	__extl	a3, a3			# get 16-bit value
352	__exth	a6, a5			# get 16-bit mask ffffffff:ffff0000
353
354	/* Get memory address */
355
3561:
357#if XCHAL_HAVE_LOOPS
358	rsr	a4, LEND		# check if we reached LEND
359	bne	a7, a4, 1f
360	rsr	a4, LCOUNT		# and LCOUNT != 0
361	beqz	a4, 1f
362	addi	a4, a4, -1		# decrement LCOUNT and set
363	rsr	a7, LBEG		# set PC to LBEGIN
364	wsr	a4, LCOUNT
365#endif
366
3671:	wsr	a7, EPC_1		# skip store instruction
368	movi	a4, ~3
369	and	a4, a4, a8		# align memory address
370
371	/* Insert value into memory */
372
373	movi	a5, -1			# mask: ffffffff:XXXX0000
374#ifdef UNALIGNED_USER_EXCEPTION
375	addi	a4, a4, 8
376#endif
377
378	__ssa8r a8
379	__src_b	a7, a5, a6		# lo-mask  F..F0..0 (BE) 0..0F..F (LE)
380	__src_b	a6, a6, a5		# hi-mask  0..0F..F (BE) F..F0..0 (LE)
381#ifdef UNALIGNED_USER_EXCEPTION
382	l32e	a5, a4, -8
383#else
384	l32i	a5, a4, 0		# load lower address word
385#endif
386	and	a5, a5, a7		# mask
387	__sh	a7, a3 			# shift value
388	or	a5, a5, a7		# or with original value
389#ifdef UNALIGNED_USER_EXCEPTION
390	s32e	a5, a4, -8
391	l32e	a7, a4, -4
392#else
393	s32i	a5, a4, 0		# store
394	l32i	a7, a4, 4		# same for upper address word
395#endif
396	__sl	a5, a3
397	and	a6, a7, a6
398	or	a6, a6, a5
399#ifdef UNALIGNED_USER_EXCEPTION
400	s32e	a6, a4, -4
401#else
402	s32i	a6, a4, 4
403#endif
404
405	/* Done. restore stack and return */
406
407.Lexit:
408	movi	a4, 0
409	rsr	a3, EXCSAVE_1
410	s32i	a4, a3, EXC_TABLE_FIXUP
411
412	/* Restore working register */
413
414	l32i	a8, a2, PT_AREG8
415	l32i	a7, a2, PT_AREG7
416	l32i	a6, a2, PT_AREG6
417	l32i	a5, a2, PT_AREG5
418	l32i	a4, a2, PT_AREG4
419	l32i	a3, a2, PT_AREG3
420
421	/* restore SAR and return */
422
423	wsr	a0, SAR
424	l32i	a0, a2, PT_AREG0
425	l32i	a2, a2, PT_AREG2
426	rfe
427
428	/* We cannot handle this exception. */
429
430	.extern _kernel_exception
431.Linvalid_instruction_store:
432.Linvalid_instruction:
433
434	/* Restore a4...a8 and SAR, set SP, and jump to default exception. */
435
436	l32i	a8, a2, PT_AREG8
437	l32i	a7, a2, PT_AREG7
438	l32i	a6, a2, PT_AREG6
439	l32i	a5, a2, PT_AREG5
440	l32i	a4, a2, PT_AREG4
441	wsr	a0, SAR
442	mov	a1, a2
443
444	rsr	a0, PS
445        bbsi.l  a2, PS_UM_BIT, 1f     # jump if user mode
446
447	movi	a0, _kernel_exception
448	jx	a0
449
4501:	movi	a0, _user_exception
451	jx	a0
452
453
454#endif /* XCHAL_UNALIGNED_LOAD_EXCEPTION || XCHAL_UNALIGNED_STORE_EXCEPTION */
455
456