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 <linux/uaccess.h>
  16
  17 #ifndef ARCH_HAS_RELATIVE_EXTABLE
  18 #define ex_to_insn(x)   ((x)->insn)
  19 #else
  20 static 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
  30 static 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  */
  54 static 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
  66 void 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  */
  78 void 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  */
 103 const struct exception_table_entry *
 104 search_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