LXR linux/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_RELATIVE_EXTABLE
  18#define ex_to_insn(x)   ((x)->insn)
  19#else
  20static inline unsigned long ex_to_insn(const struct exception_table_entry *x)
  21{
  22        return (unsigned long)&x->insn + x->insn;
  23}
  24#endif
  25
  26#ifndef ARCH_HAS_SORT_EXTABLE
  27#ifndef ARCH_HAS_RELATIVE_EXTABLE
  28#define swap_ex         NULL
  29#else
  30static void swap_ex(void *a, void *b, int size)
  31{
  32        struct exception_table_entry *x = a, *y = b, tmp;
  33        int delta = b - a;
  34
  35        tmp = *x;
  36        x->insn = y->insn + delta;
  37        y->insn = tmp.insn - delta;
  38
  39#ifdef swap_ex_entry_fixup
  40        swap_ex_entry_fixup(x, y, tmp, delta);
  41#else
  42        x->fixup = y->fixup + delta;
  43        y->fixup = tmp.fixup - delta;
  44#endif
  45}
  46#endif /* ARCH_HAS_RELATIVE_EXTABLE */
  47
  48/*
  49 * The exception table needs to be sorted so that the binary
  50 * search that we use to find entries in it works properly.
  51 * This is used both for the kernel exception table and for
  52 * the exception tables of modules that get loaded.
  53 */
  54static int cmp_ex(const void *a, const void *b)
  55{
  56        const struct exception_table_entry *x = a, *y = b;
  57
  58        /* avoid overflow */
  59        if (ex_to_insn(x) > ex_to_insn(y))
  60                return 1;
  61        if (ex_to_insn(x) < ex_to_insn(y))
  62                return -1;
  63        return 0;
  64}
  65
  66void sort_extable(struct exception_table_entry *start,
  67                  struct exception_table_entry *finish)
  68{
  69        sort(start, finish - start, sizeof(struct exception_table_entry),
  70             cmp_ex, swap_ex);
  71}
  72
  73#ifdef CONFIG_MODULES
  74/*
  75 * If the exception table is sorted, any referring to the module init
  76 * will be at the beginning or the end.
  77 */
  78void trim_init_extable(struct module *m)
  79{
  80        /*trim the beginning*/
  81        while (m->num_exentries &&
  82               within_module_init(ex_to_insn(&m->extable[0]), m)) {
  83                m->extable++;
  84                m->num_exentries--;
  85        }
  86        /*trim the end*/
  87        while (m->num_exentries &&
  88               within_module_init(ex_to_insn(&m->extable[m->num_exentries - 1]),
  89                                  m))
  90                m->num_exentries--;
  91}
  92#endif /* CONFIG_MODULES */
  93#endif /* !ARCH_HAS_SORT_EXTABLE */
  94
  95#ifndef ARCH_HAS_SEARCH_EXTABLE
  96/*
  97 * Search one exception table for an entry corresponding to the
  98 * given instruction address, and return the address of the entry,
  99 * or NULL if none is found.
 100 * We use a binary search, and thus we assume that the table is
 101 * already sorted.
 102 */
 103const struct exception_table_entry *
 104search_extable(const struct exception_table_entry *first,
 105               const struct exception_table_entry *last,
 106               unsigned long value)
 107{
 108        while (first <= last) {
 109                const struct exception_table_entry *mid;
 110
 111                mid = ((last - first) >> 1) + first;
 112                /*
 113                 * careful, the distance between value and insn
 114                 * can be larger than MAX_LONG:
 115                 */
 116                if (ex_to_insn(mid) < value)
 117                        first = mid + 1;
 118                else if (ex_to_insn(mid) > value)
 119                        last = mid - 1;
 120                else
 121                        return mid;
 122        }
 123        return NULL;
 124}
 125#endif
 126