summaryrefslogtreecommitdiffstats
path: root/arch/powerpc/net/bpf_jit_comp.c
blob: 73619d3aeb6ceebaa9d54e652b5025234f31660c (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
/* bpf_jit_comp.c: BPF JIT compiler for PPC64
 *
 * Copyright 2011 Matt Evans <matt@ozlabs.org>, IBM Corporation
 *
 * Based on the x86 BPF compiler, by Eric Dumazet (eric.dumazet@gmail.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; version 2
 * of the License.
 */
#include <linux/moduleloader.h>
#include <asm/cacheflush.h>
#include <linux/netdevice.h>
#include <linux/filter.h>
#include "bpf_jit.h"

#ifndef __BIG_ENDIAN
/* There are endianness assumptions herein. */
#error "Little-endian PPC not supported in BPF compiler"
#endif

int bpf_jit_enable __read_mostly;


static inline void bpf_flush_icache(void *start, void *end)
{
	smp_wmb();
	flush_icache_range((unsigned long)start, (unsigned long)end);
}

static void bpf_jit_build_prologue(struct sk_filter *fp, u32 *image,
				   struct codegen_context *ctx)
{
	int i;
	const struct sock_filter *filter = fp->insns;

	if (ctx->seen & (SEEN_MEM | SEEN_DATAREF)) {
		/* Make stackframe */
		if (ctx->seen & SEEN_DATAREF) {
			/* If we call any helpers (for loads), save LR */
			EMIT(PPC_INST_MFLR | __PPC_RT(0));
			PPC_STD(0, 1, 16);

			/* Back up non-volatile regs. */
			PPC_STD(r_D, 1, -(8*(32-r_D)));
			PPC_STD(r_HL, 1, -(8*(32-r_HL)));
		}
		if (ctx->seen & SEEN_MEM) {
			/*
			 * Conditionally save regs r15-r31 as some will be used
			 * for M[] data.
			 */
			for (i = r_M; i < (r_M+16); i++) {
				if (ctx->seen & (1 << (i-r_M)))
					PPC_STD(i, 1, -(8*(32-i)));
			}
		}
		EMIT(PPC_INST_STDU | __PPC_RS(1) | __PPC_RA(1) |
		     (-BPF_PPC_STACKFRAME & 0xfffc));
	}

	if (ctx->seen & SEEN_DATAREF) {
		/*
		 * If this filter needs to access skb data,
		 * prepare r_D and r_HL:
		 *  r_HL = skb->len - skb->data_len
		 *  r_D	 = skb->data
		 */
		PPC_LWZ_OFFS(r_scratch1, r_skb, offsetof(struct sk_buff,
							 data_len));
		PPC_LWZ_OFFS(r_HL, r_skb, offsetof(struct sk_buff, len));
		PPC_SUB(r_HL, r_HL, r_scratch1);
		PPC_LD_OFFS(r_D, r_skb, offsetof(struct sk_buff, data));
	}

	if (ctx->seen & SEEN_XREG) {
		/*
		 * TODO: Could also detect whether first instr. sets X and
		 * avoid this (as below, with A).
		 */
		PPC_LI(r_X, 0);
	}

	switch (filter[0].code) {
	case BPF_S_RET_K:
	case BPF_S_LD_W_LEN:
	case BPF_S_ANC_PROTOCOL:
	case BPF_S_ANC_IFINDEX:
	case BPF_S_ANC_MARK:
	case BPF_S_ANC_RXHASH:
	case BPF_S_ANC_CPU:
	case BPF_S_ANC_QUEUE:
	case BPF_S_LD_W_ABS:
	case BPF_S_LD_H_ABS:
	case BPF_S_LD_B_ABS:
		/* first instruction sets A register (or is RET 'constant') */
		break;
	default:
		/* make sure we dont leak kernel information to user */
		PPC_LI(r_A, 0);
	}
}

static void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx)
{
	int i;

	if (ctx->seen & (SEEN_MEM | SEEN_DATAREF)) {
		PPC_ADDI(1, 1, BPF_PPC_STACKFRAME);
		if (ctx->seen & SEEN_DATAREF) {
			PPC_LD(0, 1, 16);
			PPC_MTLR(0);
			PPC_LD(r_D, 1, -(8*(32-r_D)));
			PPC_LD(r_HL, 1, -(8*(32-r_HL)));
		}
		if (ctx->seen & SEEN_MEM) {
			/* Restore any saved non-vol registers */
			for (i = r_M; i < (r_M+16); i++) {
				if (ctx->seen & (1 << (i-r_M)))
					PPC_LD(i, 1, -(8*(32-i)));
			}
		}
	}
	/* The RETs have left a return value in R3. */

	PPC_BLR();
}

/* Assemble the body code between the prologue & epilogue. */
static int bpf_jit_build_body(struct sk_filter *fp, u32 *image,
			      struct codegen_context *ctx,
			      unsigned int *addrs)
{
	const struct sock_filter *filter = fp->insns;
	int flen = fp->len;
	u8 *func;
	unsigned int true_cond;
	int i;

	/* Start of epilogue code */
	unsigned int exit_addr = addrs[flen];

	for (i = 0; i < flen; i++) {
		unsigned int K = filter[i].k;

		/*
		 * addrs[] maps a BPF bytecode address into a real offset from
		 * the start of the body code.
		 */
		addrs[i] = ctx->idx * 4;

		switch (filter[i].code) {
			/*** ALU ops ***/
		case BPF_S_ALU_ADD_X: /* A += X; */
			ctx->seen |= SEEN_XREG;
			PPC_ADD(r_A, r_A, r_X);
			break;
		case BPF_S_ALU_ADD_K: /* A += K; */
			if (!K)
				break;
			PPC_ADDI(r_A, r_A, IMM_L(K));
			if (K >= 32768)
				PPC_ADDIS(r_A, r_A, IMM_HA(K));
			break;
		case BPF_S_ALU_SUB_X: /* A -= X; */
			ctx->seen |= SEEN_XREG;
			PPC_SUB(r_A, r_A, r_X);
			break;
		case BPF_S_ALU_SUB_K: /* A -= K */
			if (!K)
				break;
			PPC_ADDI(r_A, r_A, IMM_L(-K));
			if (K >= 32768)
				PPC_ADDIS(r_A, r_A, IMM_HA(-K));
			break;
		case BPF_S_ALU_MUL_X: /* A *= X; */
			ctx->seen |= SEEN_XREG;
			PPC_MUL(r_A, r_A, r_X);
			break;
		case BPF_S_ALU_MUL_K: /* A *= K */
			if (K < 32768)
				PPC_MULI(r_A, r_A, K);
			else {
				PPC_LI32(r_scratch1, K);
				PPC_MUL(r_A, r_A, r_scratch1);
			}
			break;
		case BPF_S_ALU_DIV_X: /* A /= X; */
			ctx->seen |= SEEN_XREG;
			PPC_CMPWI(r_X, 0);
			if (ctx->pc_ret0 != -1) {
				PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]);
			} else {
				/*
				 * Exit, returning 0; first pass hits here
				 * (longer worst-case code size).
				 */
				PPC_BCC_SHORT(COND_NE, (ctx->idx*4)+12);
				PPC_LI(r_ret, 0);
				PPC_JMP(exit_addr);
			}
			PPC_DIVWU(r_A, r_A, r_X);
			break;
		case BPF_S_ALU_DIV_K: /* A = reciprocal_divide(A, K); */
			PPC_LI32(r_scratch1, K);
			/* Top 32 bits of 64bit result -> A */
			PPC_MULHWU(r_A, r_A, r_scratch1);
			break;
		case BPF_S_ALU_AND_X:
			ctx->seen |= SEEN_XREG;
			PPC_AND(r_A, r_A, r_X);
			break;
		case BPF_S_ALU_AND_K:
			if (!IMM_H(K))
				PPC_ANDI(r_A, r_A, K);
			else {
				PPC_LI32(r_scratch1, K);
				PPC_AND(r_A, r_A, r_scratch1);
			}
			break;
		case BPF_S_ALU_OR_X:
			ctx->seen |= SEEN_XREG;
			PPC_OR(r_A, r_A, r_X);
			break;
		case BPF_S_ALU_OR_K:
			if (IMM_L(K))
				PPC_ORI(r_A, r_A, IMM_L(K));
			if (K >= 65536)
				PPC_ORIS(r_A, r_A, IMM_H(K));
			break;
		case BPF_S_ALU_LSH_X: /* A <<= X; */
			ctx->seen |= SEEN_XREG;
			PPC_SLW(r_A, r_A, r_X);
			break;
		case BPF_S_ALU_LSH_K:
			if (K == 0)
				break;
			else
				PPC_SLWI(r_A, r_A, K);
			break;
		case BPF_S_ALU_RSH_X: /* A >>= X; */
			ctx->seen |= SEEN_XREG;
			PPC_SRW(r_A, r_A, r_X);
			break;
		case BPF_S_ALU_RSH_K: /* A >>= K; */
			if (K == 0)
				break;
			else
				PPC_SRWI(r_A, r_A, K);
			break;
		case BPF_S_ALU_NEG:
			PPC_NEG(r_A, r_A);
			break;
		case BPF_S_RET_K:
			PPC_LI32(r_ret, K);
			if (!K) {
				if (ctx->pc_ret0 == -1)
					ctx->pc_ret0 = i;
			}
			/*
			 * If this isn't the very last instruction, branch to
			 * the epilogue if we've stuff to clean up.  Otherwise,
			 * if there's nothing to tidy, just return.  If we /are/
			 * the last instruction, we're about to fall through to
			 * the epilogue to return.
			 */
			if (i != flen - 1) {
				/*
				 * Note: 'seen' is properly valid only on pass
				 * #2.	Both parts of this conditional are the
				 * same instruction size though, meaning the
				 * first pass will still correctly determine the
				 * code size/addresses.
				 */
				if (ctx->seen)
					PPC_JMP(exit_addr);
				else
					PPC_BLR();
			}
			break;
		case BPF_S_RET_A:
			PPC_MR(r_ret, r_A);
			if (i != flen - 1) {
				if (ctx->seen)
					PPC_JMP(exit_addr);
				else
					PPC_BLR();
			}
			break;
		case BPF_S_MISC_TAX: /* X = A */
			PPC_MR(r_X, r_A);
			break;
		case BPF_S_MISC_TXA: /* A = X */
			ctx->seen |= SEEN_XREG;
			PPC_MR(r_A, r_X);
			break;

			/*** Constant loads/M[] access ***/
		case BPF_S_LD_IMM: /* A = K */
			PPC_LI32(r_A, K);
			break;
		case BPF_S_LDX_IMM: /* X = K */
			PPC_LI32(r_X, K);
			break;
		case BPF_S_LD_MEM: /* A = mem[K] */
			PPC_MR(r_A, r_M + (K & 0xf));
			ctx->seen |= SEEN_MEM | (1<<(K & 0xf));
			break;
		case BPF_S_LDX_MEM: /* X = mem[K] */
			PPC_MR(r_X, r_M + (K & 0xf));
			ctx->seen |= SEEN_MEM | (1<<(K & 0xf));
			break;
		case BPF_S_ST: /* mem[K] = A */
			PPC_MR(r_M + (K & 0xf), r_A);
			ctx->seen |= SEEN_MEM | (1<<(K & 0xf));
			break;
		case BPF_S_STX: /* mem[K] = X */
			PPC_MR(r_M + (K & 0xf), r_X);
			ctx->seen |= SEEN_XREG | SEEN_MEM | (1<<(K & 0xf));
			break;
		case BPF_S_LD_W_LEN: /*	A = skb->len; */
			BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, len) != 4);
			PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, len));
			break;
		case BPF_S_LDX_W_LEN: /* X = skb->len; */
			PPC_LWZ_OFFS(r_X, r_skb, offsetof(struct sk_buff, len));
			break;

			/*** Ancillary info loads ***/

			/* None of the BPF_S_ANC* codes appear to be passed by
			 * sk_chk_filter().  The interpreter and the x86 BPF
			 * compiler implement them so we do too -- they may be
			 * planted in future.
			 */
		case BPF_S_ANC_PROTOCOL: /* A = ntohs(skb->protocol); */
			BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff,
						  protocol) != 2);
			PPC_LHZ_OFFS(r_A, r_skb, offsetof(struct sk_buff,
							  protocol));
			/* ntohs is a NOP with BE loads. */
			break;
		case BPF_S_ANC_IFINDEX:
			PPC_LD_OFFS(r_scratch1, r_skb, offsetof(struct sk_buff,
								dev));
			PPC_CMPDI(r_scratch1, 0);
			if (ctx->pc_ret0 != -1) {
				PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]);
			} else {
				/* Exit, returning 0; first pass hits here. */
				PPC_BCC_SHORT(COND_NE, (ctx->idx*4)+12);
				PPC_LI(r_ret, 0);
				PPC_JMP(exit_addr);
			}
			BUILD_BUG_ON(FIELD_SIZEOF(struct net_device,
						  ifindex) != 4);
			PPC_LWZ_OFFS(r_A, r_scratch1,
				     offsetof(struct net_device, ifindex));
			break;
		case BPF_S_ANC_MARK:
			BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, mark) != 4);
			PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff,
							  mark));
			break;
		case BPF_S_ANC_RXHASH:
			BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, rxhash) != 4);
			PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff,
							  rxhash));
			break;
		case BPF_S_ANC_QUEUE:
			BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff,
						  queue_mapping) != 2);
			PPC_LHZ_OFFS(r_A, r_skb, offsetof(struct sk_buff,
							  queue_mapping));
			break;
		case BPF_S_ANC_CPU:
#ifdef CONFIG_SMP
			/*
			 * PACA ptr is r13:
			 * raw_smp_processor_id() = local_paca->paca_index
			 */
			BUILD_BUG_ON(FIELD_SIZEOF(struct paca_struct,
						  paca_index) != 2);
			PPC_LHZ_OFFS(r_A, 13,
				     offsetof(struct paca_struct, paca_index));
#else
			PPC_LI(r_A, 0);
#endif
			break;

			/*** Absolute loads from packet header/data ***/
		case BPF_S_LD_W_ABS:
			func = sk_load_word;
			goto common_load;
		case BPF_S_LD_H_ABS:
			func = sk_load_half;
			goto common_load;
		case BPF_S_LD_B_ABS:
			func = sk_load_byte;
		common_load:
			/*
			 * Load from [K].  Reference with the (negative)
			 * SKF_NET_OFF/SKF_LL_OFF offsets is unsupported.
			 */
			ctx->seen |= SEEN_DATAREF;
			if ((int)K < 0)
				return -ENOTSUPP;
			PPC_LI64(r_scratch1, func);
			PPC_MTLR(r_scratch1);
			PPC_LI32(r_addr, K);
			PPC_BLRL();
			/*
			 * Helper returns 'lt' condition on error, and an
			 * appropriate return value in r3
			 */
			PPC_BCC(COND_LT, exit_addr);
			break;

			/*** Indirect loads from packet header/data ***/
		case BPF_S_LD_W_IND:
			func = sk_load_word;
			goto common_load_ind;
		case BPF_S_LD_H_IND:
			func = sk_load_half;
			goto common_load_ind;
		case BPF_S_LD_B_IND:
			func = sk_load_byte;
		common_load_ind:
			/*
			 * Load from [X + K].  Negative offsets are tested for
			 * in the helper functions, and result in a 'ret 0'.
			 */
			ctx->seen |= SEEN_DATAREF | SEEN_XREG;
			PPC_LI64(r_scratch1, func);
			PPC_MTLR(r_scratch1);
			PPC_ADDI(r_addr, r_X, IMM_L(K));
			if (K >= 32768)
				PPC_ADDIS(r_addr, r_addr, IMM_HA(K));
			PPC_BLRL();
			/* If error, cr0.LT set */
			PPC_BCC(COND_LT, exit_addr);
			break;

		case BPF_S_LDX_B_MSH:
			/*
			 * x86 version drops packet (RET 0) when K<0, whereas
			 * interpreter does allow K<0 (__load_pointer, special
			 * ancillary data).  common_load returns ENOTSUPP if K<0,
			 * so we fall back to interpreter & filter works.
			 */
			func = sk_load_byte_msh;
			goto common_load;
			break;

			/*** Jump and branches ***/
		case BPF_S_JMP_JA:
			if (K != 0)
				PPC_JMP(addrs[i + 1 + K]);
			break;

		case BPF_S_JMP_JGT_K:
		case BPF_S_JMP_JGT_X:
			true_cond = COND_GT;
			goto cond_branch;
		case BPF_S_JMP_JGE_K:
		case BPF_S_JMP_JGE_X:
			true_cond = COND_GE;
			goto cond_branch;
		case BPF_S_JMP_JEQ_K:
		case BPF_S_JMP_JEQ_X:
			true_cond = COND_EQ;
			goto cond_branch;
		case BPF_S_JMP_JSET_K:
		case BPF_S_JMP_JSET_X:
			true_cond = COND_NE;
			/* Fall through */
		cond_branch:
			/* same targets, can avoid doing the test :) */
			if (filter[i].jt == filter[i].jf) {
				if (filter[i].jt > 0)
					PPC_JMP(addrs[i + 1 + filter[i].jt]);
				break;
			}

			switch (filter[i].code) {
			case BPF_S_JMP_JGT_X:
			case BPF_S_JMP_JGE_X:
			case BPF_S_JMP_JEQ_X:
				ctx->seen |= SEEN_XREG;
				PPC_CMPLW(r_A, r_X);
				break;
			case BPF_S_JMP_JSET_X:
				ctx->seen |= SEEN_XREG;
				PPC_AND_DOT(r_scratch1, r_A, r_X);
				break;
			case BPF_S_JMP_JEQ_K:
			case BPF_S_JMP_JGT_K:
			case BPF_S_JMP_JGE_K:
				if (K < 32768)
					PPC_CMPLWI(r_A, K);
				else {
					PPC_LI32(r_scratch1, K);
					PPC_CMPLW(r_A, r_scratch1);
				}
				break;
			case BPF_S_JMP_JSET_K:
				if (K < 32768)
					/* PPC_ANDI is /only/ dot-form */
					PPC_ANDI(r_scratch1, r_A, K);
				else {
					PPC_LI32(r_scratch1, K);
					PPC_AND_DOT(r_scratch1, r_A,
						    r_scratch1);
				}
				break;
			}
			/* Sometimes branches are constructed "backward", with
			 * the false path being the branch and true path being
			 * a fallthrough to the next instruction.
			 */
			if (filter[i].jt == 0)
				/* Swap the sense of the branch */
				PPC_BCC(true_cond ^ COND_CMP_TRUE,
					addrs[i + 1 + filter[i].jf]);
			else {
				PPC_BCC(true_cond, addrs[i + 1 + filter[i].jt]);
				if (filter[i].jf != 0)
					PPC_JMP(addrs[i + 1 + filter[i].jf]);
			}
			break;
		default:
			/* The filter contains something cruel & unusual.
			 * We don't handle it, but also there shouldn't be
			 * anything missing from our list.
			 */
			if (printk_ratelimit())
				pr_err("BPF filter opcode %04x (@%d) unsupported\n",
				       filter[i].code, i);
			return -ENOTSUPP;
		}

	}
	/* Set end-of-body-code address for exit. */
	addrs[i] = ctx->idx * 4;

	return 0;
}

void bpf_jit_compile(struct sk_filter *fp)
{
	unsigned int proglen;
	unsigned int alloclen;
	u32 *image = NULL;
	u32 *code_base;
	unsigned int *addrs;
	struct codegen_context cgctx;
	int pass;
	int flen = fp->len;

	if (!bpf_jit_enable)
		return;

	addrs = kzalloc((flen+1) * sizeof(*addrs), GFP_KERNEL);
	if (addrs == NULL)
		return;

	/*
	 * There are multiple assembly passes as the generated code will change
	 * size as it settles down, figuring out the max branch offsets/exit
	 * paths required.
	 *
	 * The range of standard conditional branches is +/- 32Kbytes.	Since
	 * BPF_MAXINSNS = 4096, we can only jump from (worst case) start to
	 * finish with 8 bytes/instruction.  Not feasible, so long jumps are
	 * used, distinct from short branches.
	 *
	 * Current:
	 *
	 * For now, both branch types assemble to 2 words (short branches padded
	 * with a NOP); this is less efficient, but assembly will always complete
	 * after exactly 3 passes:
	 *
	 * First pass: No code buffer; Program is "faux-generated" -- no code
	 * emitted but maximum size of output determined (and addrs[] filled
	 * in).	 Also, we note whether we use M[], whether we use skb data, etc.
	 * All generation choices assumed to be 'worst-case', e.g. branches all
	 * far (2 instructions), return path code reduction not available, etc.
	 *
	 * Second pass: Code buffer allocated with size determined previously.
	 * Prologue generated to support features we have seen used.  Exit paths
	 * determined and addrs[] is filled in again, as code may be slightly
	 * smaller as a result.
	 *
	 * Third pass: Code generated 'for real', and branch destinations
	 * determined from now-accurate addrs[] map.
	 *
	 * Ideal:
	 *
	 * If we optimise this, near branches will be shorter.	On the
	 * first assembly pass, we should err on the side of caution and
	 * generate the biggest code.  On subsequent passes, branches will be
	 * generated short or long and code size will reduce.  With smaller
	 * code, more branches may fall into the short category, and code will
	 * reduce more.
	 *
	 * Finally, if we see one pass generate code the same size as the
	 * previous pass we have converged and should now generate code for
	 * real.  Allocating at the end will also save the memory that would
	 * otherwise be wasted by the (small) current code shrinkage.
	 * Preferably, we should do a small number of passes (e.g. 5) and if we
	 * haven't converged by then, get impatient and force code to generate
	 * as-is, even if the odd branch would be left long.  The chances of a
	 * long jump are tiny with all but the most enormous of BPF filter
	 * inputs, so we should usually converge on the third pass.
	 */

	cgctx.idx = 0;
	cgctx.seen = 0;
	cgctx.pc_ret0 = -1;
	/* Scouting faux-generate pass 0 */
	if (bpf_jit_build_body(fp, 0, &cgctx, addrs))
		/* We hit something illegal or unsupported. */
		goto out;

	/*
	 * Pretend to build prologue, given the features we've seen.  This will
	 * update ctgtx.idx as it pretends to output instructions, then we can
	 * calculate total size from idx.
	 */
	bpf_jit_build_prologue(fp, 0, &cgctx);
	bpf_jit_build_epilogue(0, &cgctx);

	proglen = cgctx.idx * 4;
	alloclen = proglen + FUNCTION_DESCR_SIZE;
	image = module_alloc(max_t(unsigned int, alloclen,
				   sizeof(struct work_struct)));
	if (!image)
		goto out;

	code_base = image + (FUNCTION_DESCR_SIZE/4);

	/* Code generation passes 1-2 */
	for (pass = 1; pass < 3; pass++) {
		/* Now build the prologue, body code & epilogue for real. */
		cgctx.idx = 0;
		bpf_jit_build_prologue(fp, code_base, &cgctx);
		bpf_jit_build_body(fp, code_base, &cgctx, addrs);
		bpf_jit_build_epilogue(code_base, &cgctx);

		if (bpf_jit_enable > 1)
			pr_info("Pass %d: shrink = %d, seen = 0x%x\n", pass,
				proglen - (cgctx.idx * 4), cgctx.seen);
	}

	if (bpf_jit_enable > 1)
		pr_info("flen=%d proglen=%u pass=%d image=%p\n",
		       flen, proglen, pass, image);

	if (image) {
		if (bpf_jit_enable > 1)
			print_hex_dump(KERN_ERR, "JIT code: ",
				       DUMP_PREFIX_ADDRESS,
				       16, 1, code_base,
				       proglen, false);

		bpf_flush_icache(code_base, code_base + (proglen/4));
		/* Function descriptor nastiness: Address + TOC */
		((u64 *)image)[0] = (u64)code_base;
		((u64 *)image)[1] = local_paca->kernel_toc;
		fp->bpf_func = (void *)image;
	}
out:
	kfree(addrs);
	return;
}

static void jit_free_defer(struct work_struct *arg)
{
	module_free(NULL, arg);
}

/* run from softirq, we must use a work_struct to call
 * module_free() from process context
 */
void bpf_jit_free(struct sk_filter *fp)
{
	if (fp->bpf_func != sk_run_filter) {
		struct work_struct *work = (struct work_struct *)fp->bpf_func;

		INIT_WORK(work, jit_free_defer);
		schedule_work(work);
	}
}