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