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/bsearch.h>
  13 #include <linux/module.h>
  14 #include <linux/init.h>
  15 #include <linux/sort.h>
  16 #include <linux/uaccess.h>
  17
  18 #ifndef ARCH_HAS_RELATIVE_EXTABLE
  19 #define ex_to_insn(x)   ((x)->insn)
  20 #else
  21 static inline unsigned long ex_to_insn(const struct exception_table_entry *x)
  22 {
  23         return (unsigned long)&x->insn + x->insn;
  24 }
  25 #endif
  26
  27 #ifndef ARCH_HAS_SORT_EXTABLE
  28 #ifndef ARCH_HAS_RELATIVE_EXTABLE
  29 #define swap_ex         NULL
  30 #else
  31 static void swap_ex(void *a, void *b, int size)
  32 {
  33         struct exception_table_entry *x = a, *y = b, tmp;
  34         int delta = b - a;
  35
  36         tmp = *x;
  37         x->insn = y->insn + delta;
  38         y->insn = tmp.insn - delta;
  39
  40 #ifdef swap_ex_entry_fixup
  41         swap_ex_entry_fixup(x, y, tmp, delta);
  42 #else
  43         x->fixup = y->fixup + delta;
  44         y->fixup = tmp.fixup - delta;
  45 #endif
  46 }
  47 #endif /* ARCH_HAS_RELATIVE_EXTABLE */
  48
  49 /*
  50  * The exception table needs to be sorted so that the binary
  51  * search that we use to find entries in it works properly.
  52  * This is used both for the kernel exception table and for
  53  * the exception tables of modules that get loaded.
  54  */
  55 static int cmp_ex_sort(const void *a, const void *b)
  56 {
  57         const struct exception_table_entry *x = a, *y = b;
  58
  59         /* avoid overflow */
  60         if (ex_to_insn(x) > ex_to_insn(y))
  61                 return 1;
  62         if (ex_to_insn(x) < ex_to_insn(y))
  63                 return -1;
  64         return 0;
  65 }
  66
  67 void sort_extable(struct exception_table_entry *start,
  68                   struct exception_table_entry *finish)
  69 {
  70         sort(start, finish - start, sizeof(struct exception_table_entry),
  71              cmp_ex_sort, swap_ex);
  72 }
  73
  74 #ifdef CONFIG_MODULES
  75 /*
  76  * If the exception table is sorted, any referring to the module init
  77  * will be at the beginning or the end.
  78  */
  79 void trim_init_extable(struct module *m)
  80 {
  81         /*trim the beginning*/
  82         while (m->num_exentries &&
  83                within_module_init(ex_to_insn(&m->extable[0]), m)) {
  84                 m->extable++;
  85                 m->num_exentries--;
  86         }
  87         /*trim the end*/
  88         while (m->num_exentries &&
  89                within_module_init(ex_to_insn(&m->extable[m->num_exentries - 1]),
  90                                   m))
  91                 m->num_exentries--;
  92 }
  93 #endif /* CONFIG_MODULES */
  94 #endif /* !ARCH_HAS_SORT_EXTABLE */
  95
  96 #ifndef ARCH_HAS_SEARCH_EXTABLE
  97
  98 static int cmp_ex_search(const void *key, const void *elt)
  99 {
 100         const struct exception_table_entry *_elt = elt;
 101         unsigned long _key = *(unsigned long *)key;
 102
 103         /* avoid overflow */
 104         if (_key > ex_to_insn(_elt))
 105                 return 1;
 106         if (_key < ex_to_insn(_elt))
 107                 return -1;
 108         return 0;
 109 }
 110
 111 /*
 112  * Search one exception table for an entry corresponding to the
 113  * given instruction address, and return the address of the entry,
 114  * or NULL if none is found.
 115  * We use a binary search, and thus we assume that the table is
 116  * already sorted.
 117  */
 118 const struct exception_table_entry *
 119 search_extable(const struct exception_table_entry *base,
 120                const size_t num,
 121                unsigned long value)
 122 {
 123         return bsearch(&value, base, num,
 124                        sizeof(struct exception_table_entry), cmp_ex_search);
 125 }
 126 #endif