C++: Improvements to reduce false alarms

cpp/ql/src/Critical/GlobalUseBeforeInit.ql

@@ -98,10 +98,25 @@ predicate callReaches(Call call, ControlFlowNode successor) {
   )
 }
 
+// To avoid many false alarms like `static int a = 1;`
+predicate initialisedAtDeclaration(GlobalVariable v) {
+  exists(VariableDeclarationEntry vde |
+    vde = v.getDefinition()
+    and vde.isDefinition()
+  )
+}
+
+// No need to initialize those variables
+predicate isStdlibVariable(GlobalVariable v) {
+  v.getName() = ["stdin", "stdout", "stderr"]
+}
+
 from GlobalVariable v, Function f
 where
   uninitialisedBefore(v, f) and
-  useFunc(v, f)
+  useFunc(v, f) and
+  not initialisedAtDeclaration(v) and
+  not isStdlibVariable(v)
 select f,
   "The variable '" + v.getName() +
     " is used in this function but may not be initialized when it is called."

cpp/ql/src/Critical/InconsistentNullnessTesting.ql

@@ -15,6 +15,8 @@ import cpp
 from StackVariable v, ControlFlowNode def, VariableAccess checked, VariableAccess unchecked
 where
   checked = v.getAnAccess() and
+  // The check can often be in a macro for handling exception
+  not checked.isInMacroExpansion() and
   dereferenced(checked) and
   unchecked = v.getAnAccess() and
   dereferenced(unchecked) and

cpp/ql/src/change-notes/2024-04-09-reduce-FP.md

@@ -0,0 +1,6 @@
+---
+category: majorAnalysis
+---
+* Reduce false positives of `GlobalUseBeforeInit.ql` and `InconsistentNullnessTesting.ql`.
+Many global variables that are initialized at declaration will be reported by `GlobalUseBeforeInit.ql`.
+When `checked` is in a macro expansion for handling exceptions, it is very likely for `InconsistentNullnessTesting.ql` to report false positives.