summaryrefslogtreecommitdiffstats
path: root/arch/powerpc/lib/code-patching.c
blob: 850f3b8f4da5e55346afbbe939987b0a0642aa7d (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
/*
 *  Copyright 2008 Michael Ellerman, IBM Corporation.
 *
 *  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; either version
 *  2 of the License, or (at your option) any later version.
 */

#include <linux/kernel.h>
#include <linux/kprobes.h>
#include <linux/vmalloc.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/cpuhotplug.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/kprobes.h>

#include <asm/pgtable.h>
#include <asm/tlbflush.h>
#include <asm/page.h>
#include <asm/code-patching.h>
#include <asm/setup.h>

static int __patch_instruction(unsigned int *exec_addr, unsigned int instr,
			       unsigned int *patch_addr)
{
	int err;

	__put_user_size(instr, patch_addr, 4, err);
	if (err)
		return err;

	asm ("dcbst 0, %0; sync; icbi 0,%1; sync; isync" :: "r" (patch_addr),
							    "r" (exec_addr));

	return 0;
}

int raw_patch_instruction(unsigned int *addr, unsigned int instr)
{
	return __patch_instruction(addr, instr, addr);
}

#ifdef CONFIG_STRICT_KERNEL_RWX
static DEFINE_PER_CPU(struct vm_struct *, text_poke_area);

static int text_area_cpu_up(unsigned int cpu)
{
	struct vm_struct *area;

	area = get_vm_area(PAGE_SIZE, VM_ALLOC);
	if (!area) {
		WARN_ONCE(1, "Failed to create text area for cpu %d\n",
			cpu);
		return -1;
	}
	this_cpu_write(text_poke_area, area);

	return 0;
}

static int text_area_cpu_down(unsigned int cpu)
{
	free_vm_area(this_cpu_read(text_poke_area));
	return 0;
}

/*
 * Run as a late init call. This allows all the boot time patching to be done
 * simply by patching the code, and then we're called here prior to
 * mark_rodata_ro(), which happens after all init calls are run. Although
 * BUG_ON() is rude, in this case it should only happen if ENOMEM, and we judge
 * it as being preferable to a kernel that will crash later when someone tries
 * to use patch_instruction().
 */
static int __init setup_text_poke_area(void)
{
	BUG_ON(!cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
		"powerpc/text_poke:online", text_area_cpu_up,
		text_area_cpu_down));

	return 0;
}
late_initcall(setup_text_poke_area);

/*
 * This can be called for kernel text or a module.
 */
static int map_patch_area(void *addr, unsigned long text_poke_addr)
{
	unsigned long pfn;
	int err;

	if (is_vmalloc_addr(addr))
		pfn = vmalloc_to_pfn(addr);
	else
		pfn = __pa_symbol(addr) >> PAGE_SHIFT;

	err = map_kernel_page(text_poke_addr, (pfn << PAGE_SHIFT),
				pgprot_val(PAGE_KERNEL));

	pr_devel("Mapped addr %lx with pfn %lx:%d\n", text_poke_addr, pfn, err);
	if (err)
		return -1;

	return 0;
}

static inline int unmap_patch_area(unsigned long addr)
{
	pte_t *ptep;
	pmd_t *pmdp;
	pud_t *pudp;
	pgd_t *pgdp;

	pgdp = pgd_offset_k(addr);
	if (unlikely(!pgdp))
		return -EINVAL;

	pudp = pud_offset(pgdp, addr);
	if (unlikely(!pudp))
		return -EINVAL;

	pmdp = pmd_offset(pudp, addr);
	if (unlikely(!pmdp))
		return -EINVAL;

	ptep = pte_offset_kernel(pmdp, addr);
	if (unlikely(!ptep))
		return -EINVAL;

	pr_devel("clearing mm %p, pte %p, addr %lx\n", &init_mm, ptep, addr);

	/*
	 * In hash, pte_clear flushes the tlb, in radix, we have to
	 */
	pte_clear(&init_mm, addr, ptep);
	flush_tlb_kernel_range(addr, addr + PAGE_SIZE);

	return 0;
}

int patch_instruction(unsigned int *addr, unsigned int instr)
{
	int err;
	unsigned int *patch_addr = NULL;
	unsigned long flags;
	unsigned long text_poke_addr;
	unsigned long kaddr = (unsigned long)addr;

	/*
	 * During early early boot patch_instruction is called
	 * when text_poke_area is not ready, but we still need
	 * to allow patching. We just do the plain old patching
	 */
	if (!this_cpu_read(text_poke_area))
		return raw_patch_instruction(addr, instr);

	local_irq_save(flags);

	text_poke_addr = (unsigned long)__this_cpu_read(text_poke_area)->addr;
	if (map_patch_area(addr, text_poke_addr)) {
		err = -1;
		goto out;
	}

	patch_addr = (unsigned int *)(text_poke_addr) +
			((kaddr & ~PAGE_MASK) / sizeof(unsigned int));

	__patch_instruction(addr, instr, patch_addr);

	err = unmap_patch_area(text_poke_addr);
	if (err)
		pr_warn("failed to unmap %lx\n", text_poke_addr);

out:
	local_irq_restore(flags);

	return err;
}
#else /* !CONFIG_STRICT_KERNEL_RWX */

int patch_instruction(unsigned int *addr, unsigned int instr)
{
	return raw_patch_instruction(addr, instr);
}

#endif /* CONFIG_STRICT_KERNEL_RWX */
NOKPROBE_SYMBOL(patch_instruction);

int patch_branch(unsigned int *addr, unsigned long target, int flags)
{
	return patch_instruction(addr, create_branch(addr, target, flags));
}

int patch_branch_site(s32 *site, unsigned long target, int flags)
{
	unsigned int *addr;

	addr = (unsigned int *)((unsigned long)site + *site);
	return patch_instruction(addr, create_branch(addr, target, flags));
}

int patch_instruction_site(s32 *site, unsigned int instr)
{
	unsigned int *addr;

	addr = (unsigned int *)((unsigned long)site + *site);
	return patch_instruction(addr, instr);
}

bool is_offset_in_branch_range(long offset)
{
	/*
	 * Powerpc branch instruction is :
	 *
	 *  0         6                 30   31
	 *  +---------+----------------+---+---+
	 *  | opcode  |     LI         |AA |LK |
	 *  +---------+----------------+---+---+
	 *  Where AA = 0 and LK = 0
	 *
	 * LI is a signed 24 bits integer. The real branch offset is computed
	 * by: imm32 = SignExtend(LI:'0b00', 32);
	 *
	 * So the maximum forward branch should be:
	 *   (0x007fffff << 2) = 0x01fffffc =  0x1fffffc
	 * The maximum backward branch should be:
	 *   (0xff800000 << 2) = 0xfe000000 = -0x2000000
	 */
	return (offset >= -0x2000000 && offset <= 0x1fffffc && !(offset & 0x3));
}

/*
 * Helper to check if a given instruction is a conditional branch
 * Derived from the conditional checks in analyse_instr()
 */
bool is_conditional_branch(unsigned int instr)
{
	unsigned int opcode = instr >> 26;

	if (opcode == 16)       /* bc, bca, bcl, bcla */
		return true;
	if (opcode == 19) {
		switch ((instr >> 1) & 0x3ff) {
		case 16:        /* bclr, bclrl */
		case 528:       /* bcctr, bcctrl */
		case 560:       /* bctar, bctarl */
			return true;
		}
	}
	return false;
}
NOKPROBE_SYMBOL(is_conditional_branch);

unsigned int create_branch(const unsigned int *addr,
			   unsigned long target, int flags)
{
	unsigned int instruction;
	long offset;

	offset = target;
	if (! (flags & BRANCH_ABSOLUTE))
		offset = offset - (unsigned long)addr;

	/* Check we can represent the target in the instruction format */
	if (!is_offset_in_branch_range(offset))
		return 0;

	/* Mask out the flags and target, so they don't step on each other. */
	instruction = 0x48000000 | (flags & 0x3) | (offset & 0x03FFFFFC);

	return instruction;
}

unsigned int create_cond_branch(const unsigned int *addr,
				unsigned long target, int flags)
{
	unsigned int instruction;
	long offset;

	offset = target;
	if (! (flags & BRANCH_ABSOLUTE))
		offset = offset - (unsigned long)addr;

	/* Check we can represent the target in the instruction format */
	if (offset < -0x8000 || offset > 0x7FFF || offset & 0x3)
		return 0;

	/* Mask out the flags and target, so they don't step on each other. */
	instruction = 0x40000000 | (flags & 0x3FF0003) | (offset & 0xFFFC);

	return instruction;
}

static unsigned int branch_opcode(unsigned int instr)
{
	return (instr >> 26) & 0x3F;
}

static int instr_is_branch_iform(unsigned int instr)
{
	return branch_opcode(instr) == 18;
}

static int instr_is_branch_bform(unsigned int instr)
{
	return branch_opcode(instr) == 16;
}

int instr_is_relative_branch(unsigned int instr)
{
	if (instr & BRANCH_ABSOLUTE)
		return 0;

	return instr_is_branch_iform(instr) || instr_is_branch_bform(instr);
}

int instr_is_relative_link_branch(unsigned int instr)
{
	return instr_is_relative_branch(instr) && (instr & BRANCH_SET_LINK);
}

static unsigned long branch_iform_target(const unsigned int *instr)
{
	signed long imm;

	imm = *instr & 0x3FFFFFC;

	/* If the top bit of the immediate value is set this is negative */
	if (imm & 0x2000000)
		imm -= 0x4000000;

	if ((*instr & BRANCH_ABSOLUTE) == 0)
		imm += (unsigned long)instr;

	return (unsigned long)imm;
}

static unsigned long branch_bform_target(const unsigned int *instr)
{
	signed long imm;

	imm = *instr & 0xFFFC;

	/* If the top bit of the immediate value is set this is negative */
	if (imm & 0x8000)
		imm -= 0x10000;

	if ((*instr & BRANCH_ABSOLUTE) == 0)
		imm += (unsigned long)instr;

	return (unsigned long)imm;
}

unsigned long branch_target(const unsigned int *instr)
{
	if (instr_is_branch_iform(*instr))
		return branch_iform_target(instr);
	else if (instr_is_branch_bform(*instr))
		return branch_bform_target(instr);

	return 0;
}

int instr_is_branch_to_addr(const unsigned int *instr, unsigned long addr)
{
	if (instr_is_branch_iform(*instr) || instr_is_branch_bform(*instr))
		return branch_target(instr) == addr;

	return 0;
}

unsigned int translate_branch(const unsigned int *dest, const unsigned int *src)
{
	unsigned long target;

	target = branch_target(src);

	if (instr_is_branch_iform(*src))
		return create_branch(dest, target, *src);
	else if (instr_is_branch_bform(*src))
		return create_cond_branch(dest, target, *src);

	return 0;
}

#ifdef CONFIG_PPC_BOOK3E_64
void __patch_exception(int exc, unsigned long addr)
{
	extern unsigned int interrupt_base_book3e;
	unsigned int *ibase = &interrupt_base_book3e;

	/* Our exceptions vectors start with a NOP and -then- a branch
	 * to deal with single stepping from userspace which stops on
	 * the second instruction. Thus we need to patch the second
	 * instruction of the exception, not the first one
	 */

	patch_branch(ibase + (exc / 4) + 1, addr, 0);
}
#endif

#ifdef CONFIG_CODE_PATCHING_SELFTEST

static void __init test_trampoline(void)
{
	asm ("nop;\n");
}

#define check(x)	\
	if (!(x)) printk("code-patching: test failed at line %d\n", __LINE__);

static void __init test_branch_iform(void)
{
	unsigned int instr;
	unsigned long addr;

	addr = (unsigned long)&instr;

	/* The simplest case, branch to self, no flags */
	check(instr_is_branch_iform(0x48000000));
	/* All bits of target set, and flags */
	check(instr_is_branch_iform(0x4bffffff));
	/* High bit of opcode set, which is wrong */
	check(!instr_is_branch_iform(0xcbffffff));
	/* Middle bits of opcode set, which is wrong */
	check(!instr_is_branch_iform(0x7bffffff));

	/* Simplest case, branch to self with link */
	check(instr_is_branch_iform(0x48000001));
	/* All bits of targets set */
	check(instr_is_branch_iform(0x4bfffffd));
	/* Some bits of targets set */
	check(instr_is_branch_iform(0x4bff00fd));
	/* Must be a valid branch to start with */
	check(!instr_is_branch_iform(0x7bfffffd));

	/* Absolute branch to 0x100 */
	instr = 0x48000103;
	check(instr_is_branch_to_addr(&instr, 0x100));
	/* Absolute branch to 0x420fc */
	instr = 0x480420ff;
	check(instr_is_branch_to_addr(&instr, 0x420fc));
	/* Maximum positive relative branch, + 20MB - 4B */
	instr = 0x49fffffc;
	check(instr_is_branch_to_addr(&instr, addr + 0x1FFFFFC));
	/* Smallest negative relative branch, - 4B */
	instr = 0x4bfffffc;
	check(instr_is_branch_to_addr(&instr, addr - 4));
	/* Largest negative relative branch, - 32 MB */
	instr = 0x4a000000;
	check(instr_is_branch_to_addr(&instr, addr - 0x2000000));

	/* Branch to self, with link */
	instr = create_branch(&instr, addr, BRANCH_SET_LINK);
	check(instr_is_branch_to_addr(&instr, addr));

	/* Branch to self - 0x100, with link */
	instr = create_branch(&instr, addr - 0x100, BRANCH_SET_LINK);
	check(instr_is_branch_to_addr(&instr, addr - 0x100));

	/* Branch to self + 0x100, no link */
	instr = create_branch(&instr, addr + 0x100, 0);
	check(instr_is_branch_to_addr(&instr, addr + 0x100));

	/* Maximum relative negative offset, - 32 MB */
	instr = create_branch(&instr, addr - 0x2000000, BRANCH_SET_LINK);
	check(instr_is_branch_to_addr(&instr, addr - 0x2000000));

	/* Out of range relative negative offset, - 32 MB + 4*/
	instr = create_branch(&instr, addr - 0x2000004, BRANCH_SET_LINK);
	check(instr == 0);

	/* Out of range relative positive offset, + 32 MB */
	instr = create_branch(&instr, addr + 0x2000000, BRANCH_SET_LINK);
	check(instr == 0);

	/* Unaligned target */
	instr = create_branch(&instr, addr + 3, BRANCH_SET_LINK);
	check(instr == 0);

	/* Check flags are masked correctly */
	instr = create_branch(&instr, addr, 0xFFFFFFFC);
	check(instr_is_branch_to_addr(&instr, addr));
	check(instr == 0x48000000);
}

static void __init test_create_function_call(void)
{
	unsigned int *iptr;
	unsigned long dest;

	/* Check we can create a function call */
	iptr = (unsigned int *)ppc_function_entry(test_trampoline);
	dest = ppc_function_entry(test_create_function_call);
	patch_instruction(iptr, create_branch(iptr, dest, BRANCH_SET_LINK));
	check(instr_is_branch_to_addr(iptr, dest));
}

static void __init test_branch_bform(void)
{
	unsigned long addr;
	unsigned int *iptr, instr, flags;

	iptr = &instr;
	addr = (unsigned long)iptr;

	/* The simplest case, branch to self, no flags */
	check(instr_is_branch_bform(0x40000000));
	/* All bits of target set, and flags */
	check(instr_is_branch_bform(0x43ffffff));
	/* High bit of opcode set, which is wrong */
	check(!instr_is_branch_bform(0xc3ffffff));
	/* Middle bits of opcode set, which is wrong */
	check(!instr_is_branch_bform(0x7bffffff));

	/* Absolute conditional branch to 0x100 */
	instr = 0x43ff0103;
	check(instr_is_branch_to_addr(&instr, 0x100));
	/* Absolute conditional branch to 0x20fc */
	instr = 0x43ff20ff;
	check(instr_is_branch_to_addr(&instr, 0x20fc));
	/* Maximum positive relative conditional branch, + 32 KB - 4B */
	instr = 0x43ff7ffc;
	check(instr_is_branch_to_addr(&instr, addr + 0x7FFC));
	/* Smallest negative relative conditional branch, - 4B */
	instr = 0x43fffffc;
	check(instr_is_branch_to_addr(&instr, addr - 4));
	/* Largest negative relative conditional branch, - 32 KB */
	instr = 0x43ff8000;
	check(instr_is_branch_to_addr(&instr, addr - 0x8000));

	/* All condition code bits set & link */
	flags = 0x3ff000 | BRANCH_SET_LINK;

	/* Branch to self */
	instr = create_cond_branch(iptr, addr, flags);
	check(instr_is_branch_to_addr(&instr, addr));

	/* Branch to self - 0x100 */
	instr = create_cond_branch(iptr, addr - 0x100, flags);
	check(instr_is_branch_to_addr(&instr, addr - 0x100));

	/* Branch to self + 0x100 */
	instr = create_cond_branch(iptr, addr + 0x100, flags);
	check(instr_is_branch_to_addr(&instr, addr + 0x100));

	/* Maximum relative negative offset, - 32 KB */
	instr = create_cond_branch(iptr, addr - 0x8000, flags);
	check(instr_is_branch_to_addr(&instr, addr - 0x8000));

	/* Out of range relative negative offset, - 32 KB + 4*/
	instr = create_cond_branch(iptr, addr - 0x8004, flags);
	check(instr == 0);

	/* Out of range relative positive offset, + 32 KB */
	instr = create_cond_branch(iptr, addr + 0x8000, flags);
	check(instr == 0);

	/* Unaligned target */
	instr = create_cond_branch(iptr, addr + 3, flags);
	check(instr == 0);

	/* Check flags are masked correctly */
	instr = create_cond_branch(iptr, addr, 0xFFFFFFFC);
	check(instr_is_branch_to_addr(&instr, addr));
	check(instr == 0x43FF0000);
}

static void __init test_translate_branch(void)
{
	unsigned long addr;
	unsigned int *p, *q;
	void *buf;

	buf = vmalloc(PAGE_ALIGN(0x2000000 + 1));
	check(buf);
	if (!buf)
		return;

	/* Simple case, branch to self moved a little */
	p = buf;
	addr = (unsigned long)p;
	patch_branch(p, addr, 0);
	check(instr_is_branch_to_addr(p, addr));
	q = p + 1;
	patch_instruction(q, translate_branch(q, p));
	check(instr_is_branch_to_addr(q, addr));

	/* Maximum negative case, move b . to addr + 32 MB */
	p = buf;
	addr = (unsigned long)p;
	patch_branch(p, addr, 0);
	q = buf + 0x2000000;
	patch_instruction(q, translate_branch(q, p));
	check(instr_is_branch_to_addr(p, addr));
	check(instr_is_branch_to_addr(q, addr));
	check(*q == 0x4a000000);

	/* Maximum positive case, move x to x - 32 MB + 4 */
	p = buf + 0x2000000;
	addr = (unsigned long)p;
	patch_branch(p, addr, 0);
	q = buf + 4;
	patch_instruction(q, translate_branch(q, p));
	check(instr_is_branch_to_addr(p, addr));
	check(instr_is_branch_to_addr(q, addr));
	check(*q == 0x49fffffc);

	/* Jump to x + 16 MB moved to x + 20 MB */
	p = buf;
	addr = 0x1000000 + (unsigned long)buf;
	patch_branch(p, addr, BRANCH_SET_LINK);
	q = buf + 0x1400000;
	patch_instruction(q, translate_branch(q, p));
	check(instr_is_branch_to_addr(p, addr));
	check(instr_is_branch_to_addr(q, addr));

	/* Jump to x + 16 MB moved to x - 16 MB + 4 */
	p = buf + 0x1000000;
	addr = 0x2000000 + (unsigned long)buf;
	patch_branch(p, addr, 0);
	q = buf + 4;
	patch_instruction(q, translate_branch(q, p));
	check(instr_is_branch_to_addr(p, addr));
	check(instr_is_branch_to_addr(q, addr));


	/* Conditional branch tests */

	/* Simple case, branch to self moved a little */
	p = buf;
	addr = (unsigned long)p;
	patch_instruction(p, create_cond_branch(p, addr, 0));
	check(instr_is_branch_to_addr(p, addr));
	q = p + 1;
	patch_instruction(q, translate_branch(q, p));
	check(instr_is_branch_to_addr(q, addr));

	/* Maximum negative case, move b . to addr + 32 KB */
	p = buf;
	addr = (unsigned long)p;
	patch_instruction(p, create_cond_branch(p, addr, 0xFFFFFFFC));
	q = buf + 0x8000;
	patch_instruction(q, translate_branch(q, p));
	check(instr_is_branch_to_addr(p, addr));
	check(instr_is_branch_to_addr(q, addr));
	check(*q == 0x43ff8000);

	/* Maximum positive case, move x to x - 32 KB + 4 */
	p = buf + 0x8000;
	addr = (unsigned long)p;
	patch_instruction(p, create_cond_branch(p, addr, 0xFFFFFFFC));
	q = buf + 4;
	patch_instruction(q, translate_branch(q, p));
	check(instr_is_branch_to_addr(p, addr));
	check(instr_is_branch_to_addr(q, addr));
	check(*q == 0x43ff7ffc);

	/* Jump to x + 12 KB moved to x + 20 KB */
	p = buf;
	addr = 0x3000 + (unsigned long)buf;
	patch_instruction(p, create_cond_branch(p, addr, BRANCH_SET_LINK));
	q = buf + 0x5000;
	patch_instruction(q, translate_branch(q, p));
	check(instr_is_branch_to_addr(p, addr));
	check(instr_is_branch_to_addr(q, addr));

	/* Jump to x + 8 KB moved to x - 8 KB + 4 */
	p = buf + 0x2000;
	addr = 0x4000 + (unsigned long)buf;
	patch_instruction(p, create_cond_branch(p, addr, 0));
	q = buf + 4;
	patch_instruction(q, translate_branch(q, p));
	check(instr_is_branch_to_addr(p, addr));
	check(instr_is_branch_to_addr(q, addr));

	/* Free the buffer we were using */
	vfree(buf);
}

static int __init test_code_patching(void)
{
	printk(KERN_DEBUG "Running code patching self-tests ...\n");

	test_branch_iform();
	test_branch_bform();
	test_create_function_call();
	test_translate_branch();

	return 0;
}
late_initcall(test_code_patching);

#endif /* CONFIG_CODE_PATCHING_SELFTEST */