CPP: Calls to weak functions should be considered impure.

cpp/ql/src/semmle/code/cpp/exprs/Call.qll

@@ -275,12 +275,14 @@ class FunctionCall extends Call, @funbindexpr {
   override predicate mayBeImpure() {
     this.getChild(_).mayBeImpure() or
     this.getTarget().mayHaveSideEffects() or
-    isVirtual()
+    isVirtual() or
+    getTarget().getAnAttribute().getName() = "weak"
   }
   override predicate mayBeGloballyImpure() {
     this.getChild(_).mayBeGloballyImpure() or
     this.getTarget().mayHaveSideEffects() or
-    isVirtual()
+    isVirtual() or
+    getTarget().getAnAttribute().getName() = "weak"
   }
 }
 

cpp/ql/test/query-tests/Likely Bugs/Likely Typos/ExprHasNoEffect/ExprHasNoEffect.expected

@@ -34,4 +34,3 @@
 | volatile.c:16:5:16:7 | * ... | This expression has no effect. | volatile.c:16:5:16:7 | * ... |  |
 | volatile.c:20:5:20:13 | * ... | This expression has no effect. | volatile.c:20:5:20:13 | * ... |  |
 | weak.c:18:2:18:18 | call to myNothingFunction | This expression has no effect (because $@ has no external side effects). | weak.c:2:5:2:21 | myNothingFunction | myNothingFunction |
-| weak.c:19:2:19:22 | call to myWeakNothingFunction | This expression has no effect (because $@ has no external side effects). | weak.c:9:31:9:51 | myWeakNothingFunction | myWeakNothingFunction |

cpp/ql/test/query-tests/Likely Bugs/Likely Typos/ExprHasNoEffect/weak.c

@@ -16,5 +16,5 @@ int __attribute__((__weak__)) myWeakNothingFunction()
 
 void testWeak() {
 	myNothingFunction(); // BAD
-	myWeakNothingFunction(); // GOOD [FALSE POSITIVE]
+	myWeakNothingFunction(); // GOOD
 }