Root/lib/extable.c

1/*
2 * Derived from arch/ppc/mm/extable.c and arch/i386/mm/extable.c.
3 *
4 * Copyright (C) 2004 Paul Mackerras, IBM Corp.
5 *
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public License
8 * as published by the Free Software Foundation; either version
9 * 2 of the License, or (at your option) any later version.
10 */
11
12#include <linux/module.h>
13#include <linux/init.h>
14#include <linux/sort.h>
15#include <asm/uaccess.h>
16
17#ifndef ARCH_HAS_SORT_EXTABLE
18/*
19 * The exception table needs to be sorted so that the binary
20 * search that we use to find entries in it works properly.
21 * This is used both for the kernel exception table and for
22 * the exception tables of modules that get loaded.
23 */
24static int cmp_ex(const void *a, const void *b)
25{
26    const struct exception_table_entry *x = a, *y = b;
27
28    /* avoid overflow */
29    if (x->insn > y->insn)
30        return 1;
31    if (x->insn < y->insn)
32        return -1;
33    return 0;
34}
35
36void sort_extable(struct exception_table_entry *start,
37          struct exception_table_entry *finish)
38{
39    sort(start, finish - start, sizeof(struct exception_table_entry),
40         cmp_ex, NULL);
41}
42
43#ifdef CONFIG_MODULES
44/*
45 * If the exception table is sorted, any referring to the module init
46 * will be at the beginning or the end.
47 */
48void trim_init_extable(struct module *m)
49{
50    /*trim the beginning*/
51    while (m->num_exentries && within_module_init(m->extable[0].insn, m)) {
52        m->extable++;
53        m->num_exentries--;
54    }
55    /*trim the end*/
56    while (m->num_exentries &&
57        within_module_init(m->extable[m->num_exentries-1].insn, m))
58        m->num_exentries--;
59}
60#endif /* CONFIG_MODULES */
61#endif /* !ARCH_HAS_SORT_EXTABLE */
62
63#ifndef ARCH_HAS_SEARCH_EXTABLE
64/*
65 * Search one exception table for an entry corresponding to the
66 * given instruction address, and return the address of the entry,
67 * or NULL if none is found.
68 * We use a binary search, and thus we assume that the table is
69 * already sorted.
70 */
71const struct exception_table_entry *
72search_extable(const struct exception_table_entry *first,
73           const struct exception_table_entry *last,
74           unsigned long value)
75{
76    while (first <= last) {
77        const struct exception_table_entry *mid;
78
79        mid = ((last - first) >> 1) + first;
80        /*
81         * careful, the distance between value and insn
82         * can be larger than MAX_LONG:
83         */
84        if (mid->insn < value)
85            first = mid + 1;
86        else if (mid->insn > value)
87            last = mid - 1;
88        else
89            return mid;
90        }
91        return NULL;
92}
93#endif
94

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