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  */
  24 static 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
  36 void 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  */
  48 void 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  */
  71 const struct exception_table_entry *
  72 search_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