s390/exceptions: switch to relative exception table entries
This is the s390 port of 70627654 "x86, extable: Switch to relative
exception table entries".
Reduces the size of our exception tables by 50% on 64 bit builds.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/mm/extable.c b/arch/s390/mm/extable.c
new file mode 100644
index 0000000..4d1ee88
--- /dev/null
+++ b/arch/s390/mm/extable.c
@@ -0,0 +1,81 @@
+#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 */