FORTIFY_SOURCE: add snprintf, vsnprintf

Add _FORTIFY_SOURCE support for snprintf, vsnprintf

At this time, we opt out of these protections for clang, as clang
does not implement __builtin_va_arg_pack().

http://clang.llvm.org/docs/UsersManual.html#c_unimpl_gcc

Change-Id: I73ebe5ec8dad1dca8898a76d6afb693a25f75375

libc/stdio/__snprintf_chk.c

@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <stdio.h>
+#include <stdarg.h>
+
+/*
+ * Runtime implementation of __builtin____snprintf_chk.
+ *
+ * See
+ *   http://gcc.gnu.org/onlinedocs/gcc/Object-Size-Checking.html
+ *   http://gcc.gnu.org/ml/gcc-patches/2004-09/msg02055.html
+ * for details.
+ *
+ * This snprintf check is called if _FORTIFY_SOURCE is defined and
+ * greater than 0.
+ */
+int __snprintf_chk(
+        char *dest,
+        size_t supplied_size,
+        int flags,
+        size_t dest_len_from_compiler,
+        const char *format, ...)
+{
+    va_list va;
+    int retval;
+
+    va_start(va, format);
+    retval = __vsnprintf_chk(dest, supplied_size, flags,
+                             dest_len_from_compiler, format, va);
+    va_end(va);
+
+    return retval;
+}