Support the weak variable attribute

Cargo.toml

@@ -22,7 +22,8 @@ master = ["gccjit/master"]
 default = ["master"]
 
 [dependencies]
-gccjit = "2.1"
+#gccjit = "2.1"
+gccjit = { git = "https://github.com/rust-lang/gccjit.rs" }
 
 # Local copy.
 #gccjit = { path = "../gccjit.rs" }

src/consts.rs

@@ -7,6 +7,7 @@ use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs}
 use rustc_middle::mir::interpret::{
     self, read_target_uint, ConstAllocation, ErrorHandled, Scalar as InterpScalar,
 };
+use rustc_middle::mir::mono::Linkage;
 use rustc_middle::ty::layout::LayoutOf;
 use rustc_middle::ty::{self, Instance};
 use rustc_middle::{bug, span_bug};
@@ -256,7 +257,7 @@ impl<'gcc, 'tcx> CodegenCx<'gcc, 'tcx> {
 
             if !self.tcx.is_reachable_non_generic(def_id) {
                 #[cfg(feature = "master")]
-                global.add_string_attribute(VarAttribute::Visibility(Visibility::Hidden));
+                global.add_attribute(VarAttribute::Visibility(Visibility::Hidden));
             }
 
             global
@@ -384,6 +385,10 @@ fn check_and_apply_linkage<'gcc, 'tcx>(
         let global1 =
             cx.declare_global_with_linkage(sym, cx.type_i8(), base::global_linkage_to_gcc(linkage));
 
+        if linkage == Linkage::ExternalWeak {
+            global1.add_attribute(VarAttribute::Weak);
+        }
+
         // Declare an internal global `extern_with_linkage_foo` which
         // is initialized with the address of `foo`.  If `foo` is
         // discarded during linking (for example, if `foo` has weak

src/mono_item.rs

@@ -37,7 +37,7 @@ impl<'gcc, 'tcx> PreDefineMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
         let is_tls = attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL);
         let global = self.define_global(symbol_name, gcc_type, is_tls, attrs.link_section);
         #[cfg(feature = "master")]
-        global.add_string_attribute(VarAttribute::Visibility(base::visibility_to_gcc(visibility)));
+        global.add_attribute(VarAttribute::Visibility(base::visibility_to_gcc(visibility)));
 
         // TODO(antoyo): set linkage.
         self.instances.borrow_mut().insert(instance, global);