x86, extable: Add early_fixup_exception()

Add a restricted version of fixup_exception() to be used during early
boot only.  In particular, this doesn't support the try..catch variant
since we may not have a thread_info set up yet.

This relies on the exception table being sorted already at build time.

Link: http://lkml.kernel.org/r/1334794610-5546-1-git-send-email-hpa@zytor.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/mm/extable.c

@@ -35,3 +35,20 @@ int fixup_exception(struct pt_regs *regs)
 
 	return 0;
 }
+
+/* Restricted version used during very early boot */
+int __init early_fixup_exception(unsigned long *ip)
+{
+	const struct exception_table_entry *fixup;
+
+	fixup = search_exception_tables(*ip);
+	if (fixup) {
+		if (fixup->fixup < 16)
+			return 0; /* Not supported during early boot */
+
+		*ip = fixup->fixup;
+		return 1;
+	}
+
+	return 0;
+}