extable.c

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#include <linux/module.h>
#include <linux/sort.h>
#include <asm/uaccess.h>

/*
 * Search one exception table for an entry corresponding to the
 * given instruction address, and return the address of the entry,
 * or NULL if none is found.
 * We use a binary search, and thus we assume that the table is
 * already sorted.
 */
const struct exception_table_entry *
search_extable(const struct exception_table_entry *first,
           const struct exception_table_entry *last,
           unsigned long value)
{
    const struct exception_table_entry *mid;
    unsigned long addr;

    while (first <= last) {
        mid = ((last - first) >> 1) + first;
        addr = extable_insn(mid);
        if (addr < value)
            first = mid + 1;
        else if (addr > value)
            last = mid - 1;
        else
            return mid;
    }
    return NULL;
}

/*
 * The exception table needs to be sorted so that the binary
 * search that we use to find entries in it works properly.
 * This is used both for the kernel exception table and for
 * the exception tables of modules that get loaded.
 *
 */
static int cmp_ex(const void *a, const void *b)
{
    const struct exception_table_entry *x = a, *y = b;

    /* This compare is only valid after normalization. */
    return x->insn - y->insn;
}

void sort_extable(struct exception_table_entry *start,
          struct exception_table_entry *finish)
{
    struct exception_table_entry *p;
    int i;

    /* Normalize entries to being relative to the start of the section */
    for (p = start, i = 0; p < finish; p++, i += 8)
        p->insn += i;
    sort(start, finish - start, sizeof(*start), cmp_ex, NULL);
    /* Denormalize all entries */
    for (p = start, i = 0; p < finish; p++, i += 8)
        p->insn -= i;
}

#ifdef CONFIG_MODULES
/*
 * If the exception table is sorted, any referring to the module init
 * will be at the beginning or the end.
 */
void trim_init_extable(struct module *m)
{
    /* Trim the beginning */
    while (m->num_exentries &&
           within_module_init(extable_insn(&m->extable[0]), m)) {
        m->extable++;
        m->num_exentries--;
    }
    /* Trim the end */
    while (m->num_exentries &&
           within_module_init(extable_insn(&m->extable[m->num_exentries-1]), m))
        m->num_exentries--;
}
#endif /* CONFIG_MODULES */