lib/extable.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Derived from arch/ppc/mm/extable.c and arch/i386/mm/extable.c.
   4  *
   5  * Copyright (C) 2004 Paul Mackerras, IBM Corp.
   6  */
   7
   8 #include <linux/bsearch.h>
   9 #include <linux/module.h>
  10 #include <linux/init.h>
  11 #include <linux/sort.h>
  12 #include <linux/uaccess.h>
  13 #include <linux/extable.h>
  14
  15 #ifndef ARCH_HAS_RELATIVE_EXTABLE
  16 #define ex_to_insn(x)   ((x)->insn)
  17 #else
  18 static inline unsigned long ex_to_insn(const struct exception_table_entry *x)
  19 {
  20         return (unsigned long)&x->insn + x->insn;
  21 }
  22 #endif
  23
  24 #ifndef ARCH_HAS_SORT_EXTABLE
  25 #ifndef ARCH_HAS_RELATIVE_EXTABLE
  26 #define swap_ex         NULL
  27 #else
  28 static void swap_ex(void *a, void *b, int size)
  29 {
  30         struct exception_table_entry *x = a, *y = b, tmp;
  31         int delta = b - a;
  32
  33         tmp = *x;
  34         x->insn = y->insn + delta;
  35         y->insn = tmp.insn - delta;
  36
  37 #ifdef swap_ex_entry_fixup
  38         swap_ex_entry_fixup(x, y, tmp, delta);
  39 #else
  40         x->fixup = y->fixup + delta;
  41         y->fixup = tmp.fixup - delta;
  42 #endif
  43 }
  44 #endif /* ARCH_HAS_RELATIVE_EXTABLE */
  45
  46 /*
  47  * The exception table needs to be sorted so that the binary
  48  * search that we use to find entries in it works properly.
  49  * This is used both for the kernel exception table and for
  50  * the exception tables of modules that get loaded.
  51  */
  52 static int cmp_ex_sort(const void *a, const void *b)
  53 {
  54         const struct exception_table_entry *x = a, *y = b;
  55
  56         /* avoid overflow */
  57         if (ex_to_insn(x) > ex_to_insn(y))
  58                 return 1;
  59         if (ex_to_insn(x) < ex_to_insn(y))
  60                 return -1;
  61         return 0;
  62 }
  63
  64 void sort_extable(struct exception_table_entry *start,
  65                   struct exception_table_entry *finish)
  66 {
  67         sort(start, finish - start, sizeof(struct exception_table_entry),
  68              cmp_ex_sort, swap_ex);
  69 }
  70
  71 #ifdef CONFIG_MODULES
  72 /*
  73  * If the exception table is sorted, any referring to the module init
  74  * will be at the beginning or the end.
  75  */
  76 void trim_init_extable(struct module *m)
  77 {
  78         /*trim the beginning*/
  79         while (m->num_exentries &&
  80                within_module_init(ex_to_insn(&m->extable[0]), m)) {
  81                 m->extable++;
  82                 m->num_exentries--;
  83         }
  84         /*trim the end*/
  85         while (m->num_exentries &&
  86                within_module_init(ex_to_insn(&m->extable[m->num_exentries - 1]),
  87                                   m))
  88                 m->num_exentries--;
  89 }
  90 #endif /* CONFIG_MODULES */
  91 #endif /* !ARCH_HAS_SORT_EXTABLE */
  92
  93 #ifndef ARCH_HAS_SEARCH_EXTABLE
  94
  95 static int cmp_ex_search(const void *key, const void *elt)
  96 {
  97         const struct exception_table_entry *_elt = elt;
  98         unsigned long _key = *(unsigned long *)key;
  99
 100         /* avoid overflow */
 101         if (_key > ex_to_insn(_elt))
 102                 return 1;
 103         if (_key < ex_to_insn(_elt))
 104                 return -1;
 105         return 0;
 106 }
 107
 108 /*
 109  * Search one exception table for an entry corresponding to the
 110  * given instruction address, and return the address of the entry,
 111  * or NULL if none is found.
 112  * We use a binary search, and thus we assume that the table is
 113  * already sorted.
 114  */
 115 const struct exception_table_entry *
 116 search_extable(const struct exception_table_entry *base,
 117                const size_t num,
 118                unsigned long value)
 119 {
 120         return bsearch(&value, base, num,
 121                        sizeof(struct exception_table_entry), cmp_ex_search);
 122 }
 123 #endif