Mark the metadata symbol as reachable to fix OSX not finding dylibs.

src/librustc_trans/base.rs

@@ -2508,9 +2508,7 @@ pub fn write_metadata<'a, 'tcx>(cx: &SharedCrateContext<'a, 'tcx>,
 
     let llmeta = C_bytes_in_context(cx.metadata_llcx(), &compressed[..]);
     let llconst = C_struct_in_context(cx.metadata_llcx(), &[llmeta], false);
-    let name = format!("rust_metadata_{}_{}",
-                       cx.link_meta().crate_name,
-                       cx.link_meta().crate_hash);
+    let name = cx.metadata_symbol_name();
     let buf = CString::new(name).unwrap();
     let llglobal = unsafe {
         llvm::LLVMAddGlobal(cx.metadata_llmod(), val_ty(llconst).to_ref(), buf.as_ptr())
@@ -2812,6 +2810,10 @@ pub fn trans_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
         reachable_symbols.push("main".to_string());
     }
 
+    if sess.crate_types.borrow().contains(&config::CrateTypeDylib) {
+        reachable_symbols.push(shared_ccx.metadata_symbol_name());
+    }
+
     // For the purposes of LTO or when creating a cdylib, we add to the
     // reachable set all of the upstream reachable extern fns. These functions
     // are all part of the public ABI of the final product, so we need to

src/librustc_trans/context.rs

@@ -503,6 +503,12 @@ impl<'b, 'tcx> SharedCrateContext<'b, 'tcx> {
             Substs::new(VecPerParamSpace::empty(),
                         scheme.generics.regions.map(|_| ty::ReStatic)))
     }
+
+    pub fn metadata_symbol_name(&self) -> String {
+        format!("rust_metadata_{}_{}",
+                self.link_meta().crate_name,
+                self.link_meta().crate_hash)
+    }
 }
 
 impl<'tcx> LocalCrateContext<'tcx> {