From 4df7941a9797542f461ed11730ad222c88faef81 Mon Sep 17 00:00:00 2001
From: whitequark <whitequark@whitequark.org>
Date: Wed, 23 Nov 2016 13:53:12 +0000
Subject: [PATCH] runtime: don't attempt to perform writeback if disabled in
 kernel.

Otherwise, the startup kernel session hangs.
---
 artiq/runtime.rs/libksupport/lib.rs | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/artiq/runtime.rs/libksupport/lib.rs b/artiq/runtime.rs/libksupport/lib.rs
index 027c0e3b3..08673e759 100644
--- a/artiq/runtime.rs/libksupport/lib.rs
+++ b/artiq/runtime.rs/libksupport/lib.rs
@@ -307,7 +307,10 @@ pub unsafe fn main() {
     (mem::transmute::<usize, fn()>(library.lookup("__modinit__")))();
     send(&NowSave(NOW));
 
-    attribute_writeback(library.lookup("typeinfo") as *const ());
+    let typeinfo = library.lookup("typeinfo");
+    if typeinfo != 0 {
+        attribute_writeback(typeinfo as *const ())
+    }
 
     send(&RunFinished);