summaryrefslogtreecommitdiffstats
path: root/arch/mips/kernel/branch.c
blob: 1db29957a9318f175383d17002dd64ebce8bd294 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
/*
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Copyright (C) 1996, 97, 2000, 2001 by Ralf Baechle
 * Copyright (C) 2001 MIPS Technologies, Inc.
 */
#include <linux/kernel.h>
#include <linux/sched/signal.h>
#include <linux/signal.h>
#include <linux/export.h>
#include <asm/branch.h>
#include <asm/cpu.h>
#include <asm/cpu-features.h>
#include <asm/fpu.h>
#include <asm/fpu_emulator.h>
#include <asm/inst.h>
#include <asm/mips-r2-to-r6-emul.h>
#include <asm/ptrace.h>
#include <linux/uaccess.h>

/*
 * Calculate and return exception PC in case of branch delay slot
 * for microMIPS and MIPS16e. It does not clear the ISA mode bit.
 */
int __isa_exception_epc(struct pt_regs *regs)
{
	unsigned short inst;
	long epc = regs->cp0_epc;

	/* Calculate exception PC in branch delay slot. */
	if (__get_user(inst, (u16 __user *) msk_isa16_mode(epc))) {
		/* This should never happen because delay slot was checked. */
		force_sig(SIGSEGV);
		return epc;
	}
	if (cpu_has_mips16) {
		union mips16e_instruction inst_mips16e;

		inst_mips16e.full = inst;
		if (inst_mips16e.ri.opcode == MIPS16e_jal_op)
			epc += 4;
		else
			epc += 2;
	} else if (mm_insn_16bit(inst))
		epc += 2;
	else
		epc += 4;

	return epc;
}

/* (microMIPS) Convert 16-bit register encoding to 32-bit register encoding. */
static const unsigned int reg16to32map[8] = {16, 17, 2, 3, 4, 5, 6, 7};

int __mm_isBranchInstr(struct pt_regs *regs, struct mm_decoded_insn dec_insn,
		       unsigned long *contpc)
{
	union mips_instruction insn = (union mips_instruction)dec_insn.insn;

	if (!cpu_has_mmips)
		return 0;

	switch (insn.mm_i_format.opcode) {
	case mm_pool32a_op:
		if ((insn.mm_i_format.simmediate & MM_POOL32A_MINOR_MASK) ==
		    mm_pool32axf_op) {
			switch (insn.mm_i_format.simmediate >>
				MM_POOL32A_MINOR_SHIFT) {
			case mm_jalr_op:
			case mm_jalrhb_op:
			case mm_jalrs_op:
			case mm_jalrshb_op:
				if (insn.mm_i_format.rt != 0)	/* Not mm_jr */
					regs->regs[insn.mm_i_format.rt] =
						regs->cp0_epc +
						dec_insn.pc_inc +
						dec_insn.next_pc_inc;
				*contpc = regs->regs[insn.mm_i_format.rs];
				return 1;
			}
		}
		break;
	case mm_pool32i_op:
		switch (insn.mm_i_format.rt) {
		case mm_bltzals_op:
		case mm_bltzal_op:
			regs->regs[31] = regs->cp0_epc +
				dec_insn.pc_inc +
				dec_insn.next_pc_inc;
			/* Fall through */
		case mm_bltz_op:
			if ((long)regs->regs[insn.mm_i_format.rs] < 0)
				*contpc = regs->cp0_epc +
					dec_insn.pc_inc +
					(insn.mm_i_format.simmediate << 1);
			else
				*contpc = regs->cp0_epc +
					dec_insn.pc_inc +
					dec_insn.next_pc_inc;
			return 1;
		case mm_bgezals_op:
		case mm_bgezal_op:
			regs->regs[31] = regs->cp0_epc +
					dec_insn.pc_inc +
					dec_insn.next_pc_inc;
			/* Fall through */
		case mm_bgez_op:
			if ((long)regs->regs[insn.mm_i_format.rs] >= 0)
				*contpc = regs->cp0_epc +
					dec_insn.pc_inc +
					(insn.mm_i_format.simmediate << 1);
			else
				*contpc = regs->cp0_epc +
					dec_insn.pc_inc +
					dec_insn.next_pc_inc;
			return 1;
		case mm_blez_op:
			if ((long)regs->regs[insn.mm_i_format.rs] <= 0)
				*contpc = regs->cp0_epc +
					dec_insn.pc_inc +
					(insn.mm_i_format.simmediate << 1);
			else
				*contpc = regs->cp0_epc +
					dec_insn.pc_inc +
					dec_insn.next_pc_inc;
			return 1;
		case mm_bgtz_op:
			if ((long)regs->regs[insn.mm_i_format.rs] <= 0)
				*contpc = regs->cp0_epc +
					dec_insn.pc_inc +
					(insn.mm_i_format.simmediate << 1);
			else
				*contpc = regs->cp0_epc +
					dec_insn.pc_inc +
					dec_insn.next_pc_inc;
			return 1;
#ifdef CONFIG_MIPS_FP_SUPPORT
		case mm_bc2f_op:
		case mm_bc1f_op: {
			int bc_false = 0;
			unsigned int fcr31;
			unsigned int bit;

			bc_false = 1;
			/* Fall through */
		case mm_bc2t_op:
		case mm_bc1t_op:
			preempt_disable();
			if (is_fpu_owner())
			        fcr31 = read_32bit_cp1_register(CP1_STATUS);
			else
				fcr31 = current->thread.fpu.fcr31;
			preempt_enable();

			if (bc_false)
				fcr31 = ~fcr31;

			bit = (insn.mm_i_format.rs >> 2);
			bit += (bit != 0);
			bit += 23;
			if (fcr31 & (1 << bit))
				*contpc = regs->cp0_epc +
					dec_insn.pc_inc +
					(insn.mm_i_format.simmediate << 1);
			else
				*contpc = regs->cp0_epc +
					dec_insn.pc_inc + dec_insn.next_pc_inc;
			return 1;
		}
#endif /* CONFIG_MIPS_FP_SUPPORT */
		}
		break;
	case mm_pool16c_op:
		switch (insn.mm_i_format.rt) {
		case mm_jalr16_op:
		case mm_jalrs16_op:
			regs->regs[31] = regs->cp0_epc +
				dec_insn.pc_inc + dec_insn.next_pc_inc;
			/* Fall through */
		case mm_jr16_op:
			*contpc = regs->regs[insn.mm_i_format.rs];
			return 1;
		}
		break;
	case mm_beqz16_op:
		if ((long)regs->regs[reg16to32map[insn.mm_b1_format.rs]] == 0)
			*contpc = regs->cp0_epc +
				dec_insn.pc_inc +
				(insn.mm_b1_format.simmediate << 1);
		else
			*contpc = regs->cp0_epc +
				dec_insn.pc_inc + dec_insn.next_pc_inc;
		return 1;
	case mm_bnez16_op:
		if ((long)regs->regs[reg16to32map[insn.mm_b1_format.rs]] != 0)
			*contpc = regs->cp0_epc +
				dec_insn.pc_inc +
				(insn.mm_b1_format.simmediate << 1);
		else
			*contpc = regs->cp0_epc +
				dec_insn.pc_inc + dec_insn.next_pc_inc;
		return 1;
	case mm_b16_op:
		*contpc = regs->cp0_epc + dec_insn.pc_inc +
			 (insn.mm_b0_format.simmediate << 1);
		return 1;
	case mm_beq32_op:
		if (regs->regs[insn.mm_i_format.rs] ==
		    regs->regs[insn.mm_i_format.rt])
			*contpc = regs->cp0_epc +
				dec_insn.pc_inc +
				(insn.mm_i_format.simmediate << 1);
		else
			*contpc = regs->cp0_epc +
				dec_insn.pc_inc +
				dec_insn.next_pc_inc;
		return 1;
	case mm_bne32_op:
		if (regs->regs[insn.mm_i_format.rs] !=
		    regs->regs[insn.mm_i_format.rt])
			*contpc = regs->cp0_epc +
				dec_insn.pc_inc +
				(insn.mm_i_format.simmediate << 1);
		else
			*contpc = regs->cp0_epc +
				dec_insn.pc_inc + dec_insn.next_pc_inc;
		return 1;
	case mm_jalx32_op:
		regs->regs[31] = regs->cp0_epc +
			dec_insn.pc_inc + dec_insn.next_pc_inc;
		*contpc = regs->cp0_epc + dec_insn.pc_inc;
		*contpc >>= 28;
		*contpc <<= 28;
		*contpc |= (insn.j_format.target << 2);
		return 1;
	case mm_jals32_op:
	case mm_jal32_op:
		regs->regs[31] = regs->cp0_epc +
			dec_insn.pc_inc + dec_insn.next_pc_inc;
		/* Fall through */
	case mm_j32_op:
		*contpc = regs->cp0_epc + dec_insn.pc_inc;
		*contpc >>= 27;
		*contpc <<= 27;
		*contpc |= (insn.j_format.target << 1);
		set_isa16_mode(*contpc);
		return 1;
	}
	return 0;
}

/*
 * Compute return address and emulate branch in microMIPS mode after an
 * exception only. It does not handle compact branches/jumps and cannot
 * be used in interrupt context. (Compact branches/jumps do not cause
 * exceptions.)
 */
int __microMIPS_compute_return_epc(struct pt_regs *regs)
{
	u16 __user *pc16;
	u16 halfword;
	unsigned int word;
	unsigned long contpc;
	struct mm_decoded_insn mminsn = { 0 };

	mminsn.micro_mips_mode = 1;

	/* This load never faults. */
	pc16 = (unsigned short __user *)msk_isa16_mode(regs->cp0_epc);
	__get_user(halfword, pc16);
	pc16++;
	contpc = regs->cp0_epc + 2;
	word = ((unsigned int)halfword << 16);
	mminsn.pc_inc = 2;

	if (!mm_insn_16bit(halfword)) {
		__get_user(halfword, pc16);
		pc16++;
		contpc = regs->cp0_epc + 4;
		mminsn.pc_inc = 4;
		word |= halfword;
	}
	mminsn.insn = word;

	if (get_user(halfword, pc16))
		goto sigsegv;
	mminsn.next_pc_inc = 2;
	word = ((unsigned int)halfword << 16);

	if (!mm_insn_16bit(halfword)) {
		pc16++;
		if (get_user(halfword, pc16))
			goto sigsegv;
		mminsn.next_pc_inc = 4;
		word |= halfword;
	}
	mminsn.next_insn = word;

	mm_isBranchInstr(regs, mminsn, &contpc);

	regs->cp0_epc = contpc;

	return 0;

sigsegv:
	force_sig(SIGSEGV);
	return -EFAULT;
}

/*
 * Compute return address and emulate branch in MIPS16e mode after an
 * exception only. It does not handle compact branches/jumps and cannot
 * be used in interrupt context. (Compact branches/jumps do not cause
 * exceptions.)
 */
int __MIPS16e_compute_return_epc(struct pt_regs *regs)
{
	u16 __user *addr;
	union mips16e_instruction inst;
	u16 inst2;
	u32 fullinst;
	long epc;

	epc = regs->cp0_epc;

	/* Read the instruction. */
	addr = (u16 __user *)msk_isa16_mode(epc);
	if (__get_user(inst.full, addr)) {
		force_sig(SIGSEGV);
		return -EFAULT;
	}

	switch (inst.ri.opcode) {
	case MIPS16e_extend_op:
		regs->cp0_epc += 4;
		return 0;

		/*
		 *  JAL and JALX in MIPS16e mode
		 */
	case MIPS16e_jal_op:
		addr += 1;
		if (__get_user(inst2, addr)) {
			force_sig(SIGSEGV);
			return -EFAULT;
		}
		fullinst = ((unsigned)inst.full << 16) | inst2;
		regs->regs[31] = epc + 6;
		epc += 4;
		epc >>= 28;
		epc <<= 28;
		/*
		 * JAL:5 X:1 TARGET[20-16]:5 TARGET[25:21]:5 TARGET[15:0]:16
		 *
		 * ......TARGET[15:0].................TARGET[20:16]...........
		 * ......TARGET[25:21]
		 */
		epc |=
		    ((fullinst & 0xffff) << 2) | ((fullinst & 0x3e00000) >> 3) |
		    ((fullinst & 0x1f0000) << 7);
		if (!inst.jal.x)
			set_isa16_mode(epc);	/* Set ISA mode bit. */
		regs->cp0_epc = epc;
		return 0;

		/*
		 *  J(AL)R(C)
		 */
	case MIPS16e_rr_op:
		if (inst.rr.func == MIPS16e_jr_func) {

			if (inst.rr.ra)
				regs->cp0_epc = regs->regs[31];
			else
				regs->cp0_epc =
				    regs->regs[reg16to32[inst.rr.rx]];

			if (inst.rr.l) {
				if (inst.rr.nd)
					regs->regs[31] = epc + 2;
				else
					regs->regs[31] = epc + 4;
			}
			return 0;
		}
		break;
	}

	/*
	 * All other cases have no branch delay slot and are 16-bits.
	 * Branches do not cause an exception.
	 */
	regs->cp0_epc += 2;

	return 0;
}

/**
 * __compute_return_epc_for_insn - Computes the return address and do emulate
 *				    branch simulation, if required.
 *
 * @regs:	Pointer to pt_regs
 * @insn:	branch instruction to decode
 * Return:	-EFAULT on error and forces SIGILL, and on success
 *		returns 0 or BRANCH_LIKELY_TAKEN as appropriate after
 *		evaluating the branch.
 *
 * MIPS R6 Compact branches and forbidden slots:
 *	Compact branches do not throw exceptions because they do
 *	not have delay slots. The forbidden slot instruction ($PC+4)
 *	is only executed if the branch was not taken. Otherwise the
 *	forbidden slot is skipped entirely. This means that the
 *	only possible reason to be here because of a MIPS R6 compact
 *	branch instruction is that the forbidden slot has thrown one.
 *	In that case the branch was not taken, so the EPC can be safely
 *	set to EPC + 8.
 */
int __compute_return_epc_for_insn(struct pt_regs *regs,
				   union mips_instruction insn)
{
	long epc = regs->cp0_epc;
	unsigned int dspcontrol;
	int ret = 0;

	switch (insn.i_format.opcode) {
	/*
	 * jr and jalr are in r_format format.
	 */
	case spec_op:
		switch (insn.r_format.func) {
		case jalr_op:
			regs->regs[insn.r_format.rd] = epc + 8;
			/* Fall through */
		case jr_op:
			if (NO_R6EMU && insn.r_format.func == jr_op)
				goto sigill_r2r6;
			regs->cp0_epc = regs->regs[insn.r_format.rs];
			break;
		}
		break;

	/*
	 * This group contains:
	 * bltz_op, bgez_op, bltzl_op, bgezl_op,
	 * bltzal_op, bgezal_op, bltzall_op, bgezall_op.
	 */
	case bcond_op:
		switch (insn.i_format.rt) {
		case bltzl_op:
			if (NO_R6EMU)
				goto sigill_r2r6;
			/* fall through */
		case bltz_op:
			if ((long)regs->regs[insn.i_format.rs] < 0) {
				epc = epc + 4 + (insn.i_format.simmediate << 2);
				if (insn.i_format.rt == bltzl_op)
					ret = BRANCH_LIKELY_TAKEN;
			} else
				epc += 8;
			regs->cp0_epc = epc;
			break;

		case bgezl_op:
			if (NO_R6EMU)
				goto sigill_r2r6;
			/* fall through */
		case bgez_op:
			if ((long)regs->regs[insn.i_format.rs] >= 0) {
				epc = epc + 4 + (insn.i_format.simmediate << 2);
				if (insn.i_format.rt == bgezl_op)
					ret = BRANCH_LIKELY_TAKEN;
			} else
				epc += 8;
			regs->cp0_epc = epc;
			break;

		case bltzal_op:
		case bltzall_op:
			if (NO_R6EMU && (insn.i_format.rs ||
			    insn.i_format.rt == bltzall_op))
				goto sigill_r2r6;
			regs->regs[31] = epc + 8;
			/*
			 * OK we are here either because we hit a NAL
			 * instruction or because we are emulating an
			 * old bltzal{,l} one. Let's figure out what the
			 * case really is.
			 */
			if (!insn.i_format.rs) {
				/*
				 * NAL or BLTZAL with rs == 0
				 * Doesn't matter if we are R6 or not. The
				 * result is the same
				 */
				regs->cp0_epc += 4 +
					(insn.i_format.simmediate << 2);
				break;
			}
			/* Now do the real thing for non-R6 BLTZAL{,L} */
			if ((long)regs->regs[insn.i_format.rs] < 0) {
				epc = epc + 4 + (insn.i_format.simmediate << 2);
				if (insn.i_format.rt == bltzall_op)
					ret = BRANCH_LIKELY_TAKEN;
			} else
				epc += 8;
			regs->cp0_epc = epc;
			break;

		case bgezal_op:
		case bgezall_op:
			if (NO_R6EMU && (insn.i_format.rs ||
			    insn.i_format.rt == bgezall_op))
				goto sigill_r2r6;
			regs->regs[31] = epc + 8;
			/*
			 * OK we are here either because we hit a BAL
			 * instruction or because we are emulating an
			 * old bgezal{,l} one. Let's figure out what the
			 * case really is.
			 */
			if (!insn.i_format.rs) {
				/*
				 * BAL or BGEZAL with rs == 0
				 * Doesn't matter if we are R6 or not. The
				 * result is the same
				 */
				regs->cp0_epc += 4 +
					(insn.i_format.simmediate << 2);
				break;
			}
			/* Now do the real thing for non-R6 BGEZAL{,L} */
			if ((long)regs->regs[insn.i_format.rs] >= 0) {
				epc = epc + 4 + (insn.i_format.simmediate << 2);
				if (insn.i_format.rt == bgezall_op)
					ret = BRANCH_LIKELY_TAKEN;
			} else
				epc += 8;
			regs->cp0_epc = epc;
			break;

		case bposge32_op:
			if (!cpu_has_dsp)
				goto sigill_dsp;

			dspcontrol = rddsp(0x01);

			if (dspcontrol >= 32) {
				epc = epc + 4 + (insn.i_format.simmediate << 2);
			} else
				epc += 8;
			regs->cp0_epc = epc;
			break;
		}
		break;

	/*
	 * These are unconditional and in j_format.
	 */
	case jalx_op:
	case jal_op:
		regs->regs[31] = regs->cp0_epc + 8;
		/* fall through */
	case j_op:
		epc += 4;
		epc >>= 28;
		epc <<= 28;
		epc |= (insn.j_format.target << 2);
		regs->cp0_epc = epc;
		if (insn.i_format.opcode == jalx_op)
			set_isa16_mode(regs->cp0_epc);
		break;

	/*
	 * These are conditional and in i_format.
	 */
	case beql_op:
		if (NO_R6EMU)
			goto sigill_r2r6;
		/* fall through */
	case beq_op:
		if (regs->regs[insn.i_format.rs] ==
		    regs->regs[insn.i_format.rt]) {
			epc = epc + 4 + (insn.i_format.simmediate << 2);
			if (insn.i_format.opcode == beql_op)
				ret = BRANCH_LIKELY_TAKEN;
		} else
			epc += 8;
		regs->cp0_epc = epc;
		break;

	case bnel_op:
		if (NO_R6EMU)
			goto sigill_r2r6;
		/* fall through */
	case bne_op:
		if (regs->regs[insn.i_format.rs] !=
		    regs->regs[insn.i_format.rt]) {
			epc = epc + 4 + (insn.i_format.simmediate << 2);
			if (insn.i_format.opcode == bnel_op)
				ret = BRANCH_LIKELY_TAKEN;
		} else
			epc += 8;
		regs->cp0_epc = epc;
		break;

	case blezl_op: /* not really i_format */
		if (!insn.i_format.rt && NO_R6EMU)
			goto sigill_r2r6;
		/* fall through */
	case blez_op:
		/*
		 * Compact branches for R6 for the
		 * blez and blezl opcodes.
		 * BLEZ  | rs = 0 | rt != 0  == BLEZALC
		 * BLEZ  | rs = rt != 0      == BGEZALC
		 * BLEZ  | rs != 0 | rt != 0 == BGEUC
		 * BLEZL | rs = 0 | rt != 0  == BLEZC
		 * BLEZL | rs = rt != 0      == BGEZC
		 * BLEZL | rs != 0 | rt != 0 == BGEC
		 *
		 * For real BLEZ{,L}, rt is always 0.
		 */

		if (cpu_has_mips_r6 && insn.i_format.rt) {
			if ((insn.i_format.opcode == blez_op) &&
			    ((!insn.i_format.rs && insn.i_format.rt) ||
			     (insn.i_format.rs == insn.i_format.rt)))
				regs->regs[31] = epc + 4;
			regs->cp0_epc += 8;
			break;
		}
		/* rt field assumed to be zero */
		if ((long)regs->regs[insn.i_format.rs] <= 0) {
			epc = epc + 4 + (insn.i_format.simmediate << 2);
			if (insn.i_format.opcode == blezl_op)
				ret = BRANCH_LIKELY_TAKEN;
		} else
			epc += 8;
		regs->cp0_epc = epc;
		break;

	case bgtzl_op:
		if (!insn.i_format.rt && NO_R6EMU)
			goto sigill_r2r6;
		/* fall through */
	case bgtz_op:
		/*
		 * Compact branches for R6 for the
		 * bgtz and bgtzl opcodes.
		 * BGTZ  | rs = 0 | rt != 0  == BGTZALC
		 * BGTZ  | rs = rt != 0      == BLTZALC
		 * BGTZ  | rs != 0 | rt != 0 == BLTUC
		 * BGTZL | rs = 0 | rt != 0  == BGTZC
		 * BGTZL | rs = rt != 0      == BLTZC
		 * BGTZL | rs != 0 | rt != 0 == BLTC
		 *
		 * *ZALC varint for BGTZ &&& rt != 0
		 * For real GTZ{,L}, rt is always 0.
		 */
		if (cpu_has_mips_r6 && insn.i_format.rt) {
			if ((insn.i_format.opcode == blez_op) &&
			    ((!insn.i_format.rs && insn.i_format.rt) ||
			    (insn.i_format.rs == insn.i_format.rt)))
				regs->regs[31] = epc + 4;
			regs->cp0_epc += 8;
			break;
		}

		/* rt field assumed to be zero */
		if ((long)regs->regs[insn.i_format.rs] > 0) {
			epc = epc + 4 + (insn.i_format.simmediate << 2);
			if (insn.i_format.opcode == bgtzl_op)
				ret = BRANCH_LIKELY_TAKEN;
		} else
			epc += 8;
		regs->cp0_epc = epc;
		break;

#ifdef CONFIG_MIPS_FP_SUPPORT
	/*
	 * And now the FPA/cp1 branch instructions.
	 */
	case cop1_op: {
		unsigned int bit, fcr31, reg;

		if (cpu_has_mips_r6 &&
		    ((insn.i_format.rs == bc1eqz_op) ||
		     (insn.i_format.rs == bc1nez_op))) {
			if (!init_fp_ctx(current))
				lose_fpu(1);
			reg = insn.i_format.rt;
			bit = get_fpr32(&current->thread.fpu.fpr[reg], 0) & 0x1;
			if (insn.i_format.rs == bc1eqz_op)
				bit = !bit;
			own_fpu(1);
			if (bit)
				epc = epc + 4 +
					(insn.i_format.simmediate << 2);
			else
				epc += 8;
			regs->cp0_epc = epc;

			break;
		} else {

			preempt_disable();
			if (is_fpu_owner())
			        fcr31 = read_32bit_cp1_register(CP1_STATUS);
			else
				fcr31 = current->thread.fpu.fcr31;
			preempt_enable();

			bit = (insn.i_format.rt >> 2);
			bit += (bit != 0);
			bit += 23;
			switch (insn.i_format.rt & 3) {
			case 0: /* bc1f */
			case 2: /* bc1fl */
				if (~fcr31 & (1 << bit)) {
					epc = epc + 4 +
						(insn.i_format.simmediate << 2);
					if (insn.i_format.rt == 2)
						ret = BRANCH_LIKELY_TAKEN;
				} else
					epc += 8;
				regs->cp0_epc = epc;
				break;

			case 1: /* bc1t */
			case 3: /* bc1tl */
				if (fcr31 & (1 << bit)) {
					epc = epc + 4 +
						(insn.i_format.simmediate << 2);
					if (insn.i_format.rt == 3)
						ret = BRANCH_LIKELY_TAKEN;
				} else
					epc += 8;
				regs->cp0_epc = epc;
				break;
			}
			break;
		}
	}
#endif /* CONFIG_MIPS_FP_SUPPORT */

#ifdef CONFIG_CPU_CAVIUM_OCTEON
	case lwc2_op: /* This is bbit0 on Octeon */
		if ((regs->regs[insn.i_format.rs] & (1ull<<insn.i_format.rt))
		     == 0)
			epc = epc + 4 + (insn.i_format.simmediate << 2);
		else
			epc += 8;
		regs->cp0_epc = epc;
		break;
	case ldc2_op: /* This is bbit032 on Octeon */
		if ((regs->regs[insn.i_format.rs] &
		    (1ull<<(insn.i_format.rt+32))) == 0)
			epc = epc + 4 + (insn.i_format.simmediate << 2);
		else
			epc += 8;
		regs->cp0_epc = epc;
		break;
	case swc2_op: /* This is bbit1 on Octeon */
		if (regs->regs[insn.i_format.rs] & (1ull<<insn.i_format.rt))
			epc = epc + 4 + (insn.i_format.simmediate << 2);
		else
			epc += 8;
		regs->cp0_epc = epc;
		break;
	case sdc2_op: /* This is bbit132 on Octeon */
		if (regs->regs[insn.i_format.rs] &
		    (1ull<<(insn.i_format.rt+32)))
			epc = epc + 4 + (insn.i_format.simmediate << 2);
		else
			epc += 8;
		regs->cp0_epc = epc;
		break;
#else
	case bc6_op:
		/* Only valid for MIPS R6 */
		if (!cpu_has_mips_r6)
			goto sigill_r6;
		regs->cp0_epc += 8;
		break;
	case balc6_op:
		if (!cpu_has_mips_r6)
			goto sigill_r6;
		/* Compact branch: BALC */
		regs->regs[31] = epc + 4;
		epc += 4 + (insn.i_format.simmediate << 2);
		regs->cp0_epc = epc;
		break;
	case pop66_op:
		if (!cpu_has_mips_r6)
			goto sigill_r6;
		/* Compact branch: BEQZC || JIC */
		regs->cp0_epc += 8;
		break;
	case pop76_op:
		if (!cpu_has_mips_r6)
			goto sigill_r6;
		/* Compact branch: BNEZC || JIALC */
		if (!insn.i_format.rs) {
			/* JIALC: set $31/ra */
			regs->regs[31] = epc + 4;
		}
		regs->cp0_epc += 8;
		break;
#endif
	case pop10_op:
	case pop30_op:
		/* Only valid for MIPS R6 */
		if (!cpu_has_mips_r6)
			goto sigill_r6;
		/*
		 * Compact branches:
		 * bovc, beqc, beqzalc, bnvc, bnec, bnezlac
		 */
		if (insn.i_format.rt && !insn.i_format.rs)
			regs->regs[31] = epc + 4;
		regs->cp0_epc += 8;
		break;
	}

	return ret;

sigill_dsp:
	pr_debug("%s: DSP branch but not DSP ASE - sending SIGILL.\n",
		 current->comm);
	force_sig(SIGILL);
	return -EFAULT;
sigill_r2r6:
	pr_debug("%s: R2 branch but r2-to-r6 emulator is not present - sending SIGILL.\n",
		 current->comm);
	force_sig(SIGILL);
	return -EFAULT;
sigill_r6:
	pr_debug("%s: R6 branch but no MIPSr6 ISA support - sending SIGILL.\n",
		 current->comm);
	force_sig(SIGILL);
	return -EFAULT;
}
EXPORT_SYMBOL_GPL(__compute_return_epc_for_insn);

int __compute_return_epc(struct pt_regs *regs)
{
	unsigned int __user *addr;
	long epc;
	union mips_instruction insn;

	epc = regs->cp0_epc;
	if (epc & 3)
		goto unaligned;

	/*
	 * Read the instruction
	 */
	addr = (unsigned int __user *) epc;
	if (__get_user(insn.word, addr)) {
		force_sig(SIGSEGV);
		return -EFAULT;
	}

	return __compute_return_epc_for_insn(regs, insn);

unaligned:
	printk("%s: unaligned epc - sending SIGBUS.\n", current->comm);
	force_sig(SIGBUS);
	return -EFAULT;
}

#if (defined CONFIG_KPROBES) || (defined CONFIG_UPROBES)

int __insn_is_compact_branch(union mips_instruction insn)
{
	if (!cpu_has_mips_r6)
		return 0;

	switch (insn.i_format.opcode) {
	case blezl_op:
	case bgtzl_op:
	case blez_op:
	case bgtz_op:
		/*
		 * blez[l] and bgtz[l] opcodes with non-zero rt
		 * are MIPS R6 compact branches
		 */
		if (insn.i_format.rt)
			return 1;
		break;
	case bc6_op:
	case balc6_op:
	case pop10_op:
	case pop30_op:
	case pop66_op:
	case pop76_op:
		return 1;
	}

	return 0;
}
EXPORT_SYMBOL_GPL(__insn_is_compact_branch);

#endif  /* CONFIG_KPROBES || CONFIG_UPROBES */