linux/lib/extable.c
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   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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