Extra assertions and fix for Faerie.

cranelift/faerie/src/backend.rs

@@ -211,8 +211,11 @@ impl Backend for FaerieBackend {
             ref data_decls,
             ref function_relocs,
             ref data_relocs,
+            section: ref datasection
         } = data_ctx.description();
 
+        assert!(datasection.is_none(), "Custom sections not supported");
+
         for &(offset, id) in function_relocs {
             let to = &namespace.get_function_decl(&function_decls[id]).name;
             self.artifact

cranelift/object/src/backend.rs

@@ -284,6 +284,7 @@ impl Backend for ObjectBackend {
                 };
                 self.object.section_id(section_kind)
             } else {
+                assert!(!tls, "Tls data cannot be in named section");
                 let (seg, sec) = &datasection.as_ref().unwrap();
                 self.object.add_section(seg.clone().into_bytes(), sec.clone().into_bytes(), 
                     if writable { SectionKind::Data } else { SectionKind::ReadOnlyData }