xref: /kernel/linux/linux-5.10/lib/extable.c (revision 8c2ecf20) 
1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * Derived from arch/ppc/mm/extable.c and arch/i386/mm/extable.c.
4 *
5 * Copyright (C) 2004 Paul Mackerras, IBM Corp.
6 */
7
8#include <linux/bsearch.h>
9#include <linux/module.h>
10#include <linux/init.h>
11#include <linux/sort.h>
12#include <linux/uaccess.h>
13#include <linux/extable.h>
14
15#ifndef ARCH_HAS_RELATIVE_EXTABLE
16#define ex_to_insn(x)	((x)->insn)
17#else
18static inline unsigned long ex_to_insn(const struct exception_table_entry *x)
19{
20	return (unsigned long)&x->insn + x->insn;
21}
22#endif
23
24#ifndef ARCH_HAS_SORT_EXTABLE
25#ifndef ARCH_HAS_RELATIVE_EXTABLE
26#define swap_ex		NULL
27#else
28static void swap_ex(void *a, void *b, int size)
29{
30	struct exception_table_entry *x = a, *y = b, tmp;
31	int delta = b - a;
32
33	tmp = *x;
34	x->insn = y->insn + delta;
35	y->insn = tmp.insn - delta;
36
37#ifdef swap_ex_entry_fixup
38	swap_ex_entry_fixup(x, y, tmp, delta);
39#else
40	x->fixup = y->fixup + delta;
41	y->fixup = tmp.fixup - delta;
42#endif
43}
44#endif /* ARCH_HAS_RELATIVE_EXTABLE */
45
46/*
47 * The exception table needs to be sorted so that the binary
48 * search that we use to find entries in it works properly.
49 * This is used both for the kernel exception table and for
50 * the exception tables of modules that get loaded.
51 */
52static int cmp_ex_sort(const void *a, const void *b)
53{
54	const struct exception_table_entry *x = a, *y = b;
55
56	/* avoid overflow */
57	if (ex_to_insn(x) > ex_to_insn(y))
58		return 1;
59	if (ex_to_insn(x) < ex_to_insn(y))
60		return -1;
61	return 0;
62}
63
64void sort_extable(struct exception_table_entry *start,
65		  struct exception_table_entry *finish)
66{
67	sort(start, finish - start, sizeof(struct exception_table_entry),
68	     cmp_ex_sort, swap_ex);
69}
70
71#ifdef CONFIG_MODULES
72/*
73 * If the exception table is sorted, any referring to the module init
74 * will be at the beginning or the end.
75 */
76void trim_init_extable(struct module *m)
77{
78	/*trim the beginning*/
79	while (m->num_exentries &&
80	       within_module_init(ex_to_insn(&m->extable[0]), m)) {
81		m->extable++;
82		m->num_exentries--;
83	}
84	/*trim the end*/
85	while (m->num_exentries &&
86	       within_module_init(ex_to_insn(&m->extable[m->num_exentries - 1]),
87				  m))
88		m->num_exentries--;
89}
90#endif /* CONFIG_MODULES */
91#endif /* !ARCH_HAS_SORT_EXTABLE */
92
93#ifndef ARCH_HAS_SEARCH_EXTABLE
94
95static int cmp_ex_search(const void *key, const void *elt)
96{
97	const struct exception_table_entry *_elt = elt;
98	unsigned long _key = *(unsigned long *)key;
99
100	/* avoid overflow */
101	if (_key > ex_to_insn(_elt))
102		return 1;
103	if (_key < ex_to_insn(_elt))
104		return -1;
105	return 0;
106}
107
108/*
109 * Search one exception table for an entry corresponding to the
110 * given instruction address, and return the address of the entry,
111 * or NULL if none is found.
112 * We use a binary search, and thus we assume that the table is
113 * already sorted.
114 */
115const struct exception_table_entry *
116search_extable(const struct exception_table_entry *base,
117	       const size_t num,
118	       unsigned long value)
119{
120	return bsearch(&value, base, num,
121		       sizeof(struct exception_table_entry), cmp_ex_search);
122}
123#endif
124