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>

3 files changed, 83 insertions, 2 deletions

diff --git a/arch/s390/mm/Makefile b/arch/s390/mm/Makefile
index d98fe9004a5..0f5536b0c1a 100644
--- a/arch/s390/mm/Makefile
+++ b/arch/s390/mm/Makefile
@@ -3,7 +3,7 @@
 #
 
 obj-y    := init.o fault.o extmem.o mmap.o vmem.o pgtable.o maccess.o \
-            page-states.o gup.o
+            page-states.o gup.o extable.o
 obj-$(CONFIG_CMM) += cmm.o
 obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o
 obj-$(CONFIG_DEBUG_SET_MODULE_RONX) += pageattr.o
diff --git a/arch/s390/mm/extable.c b/arch/s390/mm/extable.c
new file mode 100644
index 00000000000..4d1ee88864e
--- /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 */
diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index 8b2cac1ddbc..ac9122ca115 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -163,7 +163,7 @@ static noinline void do_no_context(struct pt_regs *regs)
         /* Are we prepared to handle this kernel fault?  */
         fixup = search_exception_tables(regs->psw.addr & PSW_ADDR_INSN);
         if (fixup) {
-                regs->psw.addr = fixup->fixup | PSW_ADDR_AMODE;
+                regs->psw.addr = extable_fixup(fixup) | PSW_ADDR_AMODE;
                 return;
         }