Error when trying to define variadic functions

They aren't yet supported by Cranelift

src/abi/mod.rs

@@ -193,6 +193,15 @@ pub(crate) fn codegen_fn_prelude<'tcx>(fx: &mut FunctionCx<'_, '_, 'tcx>, start_
     }
 
     let fn_abi = fx.fn_abi.take().unwrap();
+
+    // FIXME implement variadics in cranelift
+    if fn_abi.c_variadic {
+        fx.tcx.sess.span_fatal(
+            fx.mir.span,
+            "Defining variadic functions is not yet supported by Cranelift",
+        );
+    }
+
     let mut arg_abis_iter = fn_abi.args.iter();
 
     let func_params = fx

src/intrinsics/mod.rs

@@ -1135,6 +1135,20 @@ fn codegen_regular_intrinsic_call<'tcx>(
             // FIXME implement black_box semantics
             ret.write_cvalue(fx, a);
         };
+
+        // FIXME implement variadics in cranelift
+        va_copy, (o _dest, o _src) {
+            fx.tcx.sess.span_fatal(
+                source_info.span,
+                "Defining variadic functions is not yet supported by Cranelift",
+            );
+        };
+        va_arg | va_end, (o _valist) {
+            fx.tcx.sess.span_fatal(
+                source_info.span,
+                "Defining variadic functions is not yet supported by Cranelift",
+            );
+        };
     }
 
     let ret_block = fx.get_block(destination.unwrap());