Add error for using null characters in export_name

src/librustc_typeck/collect.rs

@@ -1898,11 +1898,18 @@ fn codegen_fn_attrs<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, id: DefId) -> Codegen
                 }
             });
         } else if attr.check_name("export_name") {
-            if let s @ Some(_) = attr.value_str() {
-                codegen_fn_attrs.export_name = s;
+            if let Some(s) = attr.value_str() {
+                if s.as_str().contains("\0") {
+                    // `#[export_name = ...]` will be converted to a null-terminated string,
+                    // so it may not contain any null characters.
+                    struct_span_err!(tcx.sess, attr.span, E0648,
+                                     "`export_name` may not contain null characters")
+                        .emit();
+                }
+                codegen_fn_attrs.export_name = Some(s);
             } else {
                 struct_span_err!(tcx.sess, attr.span, E0558,
-                                    "export_name attribute has invalid format")
+                                 "export_name attribute has invalid format")
                     .span_label(attr.span, "did you mean #[export_name=\"*\"]?")
                     .emit();
             }

src/librustc_typeck/diagnostics.rs

@@ -4545,6 +4545,14 @@ fn start(_: isize, _: *const *const u8) -> isize where (): Copy {
 ```
 "##,
 
+E0648: r##"
+`export_name` attributes may not contain null characters (`\0`).
+
+```compile_fail,E0648
+#[export_name="\0foo"] // error: `export_name` may not contain null characters
+```
+"##,
+
 E0689: r##"
 This error indicates that the numeric value for the method being passed exists
 but the type of the numeric value or binding could not be identified.

src/test/ui/error-codes/E0648.rs

@@ -0,0 +1,14 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#[export_name="\0foo"] //~ ERROR E0648
+pub fn bar() {}
+
+fn main() {}

src/test/ui/error-codes/E0648.stderr

@@ -0,0 +1,9 @@
+error[E0648]: `export_name` may not contain null characters
+  --> $DIR/E0648.rs:11:1
+   |
+LL | #[export_name="/0foo"] //~ ERROR E0648
+   | ^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0648`.