Fix FP reported in #388

change_notes/2024-02-14-fix-fp-m0-1-4.md

@@ -0,0 +1,4 @@
+- `M0-1-4` - `SingleUseMemberPODVariable.ql`:
+  - Address FP reported in #388. Include aggregrate initialization as a use of a member.
+  - Include indirect initialization of members. For example, casting a pointer to a buffer to a struct pointer.
+  - Reformat the alert message to adhere to the style-guide.

cpp/autosar/src/rules/M0-1-4/SingleUseMemberPODVariable.ql

@@ -24,5 +24,5 @@ where
   not isExcluded(v, DeadCodePackage::singleUseMemberPODVariableQuery()) and
   isSingleUseNonVolatilePODVariable(v)
 select v,
-  "Member POD variable " + v.getName() + " in " + v.getDeclaringType().getName() + " is only $@.",
-  getSingleUse(v), "used once"
+  "Member POD variable '" + v.getName() + "' in '" + v.getDeclaringType().getName() +
+    "' is only $@.", getSingleUse(v), "used once"

cpp/autosar/src/rules/M0-1-4/SingleUsePODVariable.qll

@@ -10,23 +10,69 @@ private string getConstExprValue(Variable v) {
   v.isConstexpr()
 }
 
+/**
+ * Gets the number of uses of variable `v` in an opaque assignment, where an opaqua assignment for example a cast from one type to the other and `v` is assumed to be a member of the resulting type.
+ * e.g.,
+ * struct foo {
+ *  int bar;
+ * }
+ *
+ * struct foo * v = (struct foo*)buffer;
+ */
+Expr getIndirectSubObjectAssignedValue(MemberVariable subobject) {
+  // struct foo * ptr = (struct foo*)buffer;
+  exists(Struct someStruct, Variable instanceOfSomeStruct | someStruct.getAMember() = subobject |
+    instanceOfSomeStruct.getType().(PointerType).getBaseType() = someStruct and
+    exists(Cast assignedValue |
+      // Exclude cases like struct foo * v = nullptr;
+      not assignedValue.isImplicit() and
+      // `v` is a subobject of another type that reinterprets another object. We count that as a use of `v`.
+      assignedValue.getExpr() = instanceOfSomeStruct.getAnAssignedValue() and
+      result = assignedValue
+    )
+    or
+    // struct foo; read(..., (char *)&foo);
+    instanceOfSomeStruct.getType() = someStruct and
+    exists(Call externalInitializerCall, Cast castToCharPointer, int n |
+      externalInitializerCall.getArgument(n).(AddressOfExpr).getOperand() =
+        instanceOfSomeStruct.getAnAccess() and
+      externalInitializerCall.getArgument(n) = castToCharPointer.getExpr() and
+      castToCharPointer.getType().(PointerType).getBaseType().getUnspecifiedType() instanceof
+        CharType and
+      result = externalInitializerCall
+    )
+    or
+    // the object this subject is part of is initialized and we assumes this initializes the subobject.
+    instanceOfSomeStruct.getType() = someStruct and
+    result = instanceOfSomeStruct.getInitializer().getExpr()
+  )
+}
+
 /** Gets a "use" count according to rule M0-1-4. */
 int getUseCount(Variable v) {
-  exists(int initializers |
-    // We enforce that it's a POD type variable, so if it has an initializer it is explicit
-    (if v.hasInitializer() then initializers = 1 else initializers = 0) and
-    result =
-      initializers +
-        count(VariableAccess access | access = v.getAnAccess() and not access.isCompilerGenerated())
-        + count(UserProvidedConstructorFieldInit cfi | cfi.getTarget() = v) +
-        // For constexpr variables used as template arguments, we don't see accesses (just the
-        // appropriate literals). We therefore take a conservative approach and count the number of
-        // template instantiations that use the given constant, and consider each one to be a use
-        // of the variable
-        count(ClassTemplateInstantiation cti |
-          cti.getTemplateArgument(_).(Expr).getValue() = getConstExprValue(v)
-        )
-  )
+  // We enforce that it's a POD type variable, so if it has an initializer it is explicit
+  //v.getFile().getBaseName() = "test_member.cpp" and
+  result =
+    count(getAUserInitializedValue(v)) +
+      count(VariableAccess access | access = v.getAnAccess() and not access.isCompilerGenerated()) +
+      // For constexpr variables used as template arguments, we don't see accesses (just the
+      // appropriate literals). We therefore take a conservative approach and count the number of
+      // template instantiations that use the given constant, and consider each one to be a use
+      // of the variable
+      count(ClassTemplateInstantiation cti |
+        cti.getTemplateArgument(_).(Expr).getValue() = getConstExprValue(v)
+      ) + count(getIndirectSubObjectAssignedValue(v))
+}
+
+Expr getAUserInitializedValue(Variable v) {
+  (
+    result = v.getInitializer().getExpr()
+    or
+    exists(UserProvidedConstructorFieldInit cfi | cfi.getTarget() = v and result = cfi.getExpr())
+    or
+    exists(ClassAggregateLiteral l | not l.isCompilerGenerated() | result = l.getAFieldExpr(v))
+  ) and
+  not result.isCompilerGenerated()
 }
 
 /** Gets a single use of `v`, if `isSingleUseNonVolatilePODVariable` holds. */

cpp/autosar/test/rules/M0-1-4/SingleUseMemberPODVariable.expected

@@ -1,9 +1,9 @@
-| test_global_or_namespace.cpp:16:7:16:7 | x | Member POD variable x in GA is only $@. | test_global_or_namespace.cpp:38:6:38:6 | x | used once |
-| test_global_or_namespace.cpp:54:7:54:7 | x | Member POD variable x in N1A is only $@. | test_global_or_namespace.cpp:76:6:76:6 | x | used once |
-| test_member.cpp:5:7:5:8 | m2 | Member POD variable m2 in A is only $@. | test_member.cpp:9:21:9:25 | constructor init of field m2 | used once |
-| test_member.cpp:6:7:6:8 | m3 | Member POD variable m3 in A is only $@. | test_member.cpp:10:23:10:24 | m3 | used once |
-| test_member.cpp:7:7:7:8 | m4 | Member POD variable m4 in A is only $@. | test_member.cpp:14:23:14:24 | m4 | used once |
-| test_member.cpp:18:9:18:11 | sm1 | Member POD variable sm1 in s1 is only $@. | test_member.cpp:23:6:23:8 | sm1 | used once |
-| test_member.cpp:36:7:36:8 | m1 | Member POD variable m1 in C is only $@. | test_member.cpp:39:21:39:22 | m1 | used once |
-| test_member.cpp:37:7:37:8 | m2 | Member POD variable m2 in C is only $@. | test_member.cpp:46:5:46:6 | m2 | used once |
-| test_member.cpp:55:5:55:6 | m3 | Member POD variable m3 in E<B> is only $@. | test_member.cpp:56:27:56:32 | constructor init of field m3 | used once |
+| test_global_or_namespace.cpp:16:7:16:7 | x | Member POD variable 'x' in 'GA' is only $@. | test_global_or_namespace.cpp:38:6:38:6 | x | used once |
+| test_global_or_namespace.cpp:54:7:54:7 | x | Member POD variable 'x' in 'N1A' is only $@. | test_global_or_namespace.cpp:76:6:76:6 | x | used once |
+| test_member.cpp:5:7:5:8 | m2 | Member POD variable 'm2' in 'A' is only $@. | test_member.cpp:9:21:9:25 | constructor init of field m2 | used once |
+| test_member.cpp:6:7:6:8 | m3 | Member POD variable 'm3' in 'A' is only $@. | test_member.cpp:10:23:10:24 | m3 | used once |
+| test_member.cpp:7:7:7:8 | m4 | Member POD variable 'm4' in 'A' is only $@. | test_member.cpp:14:23:14:24 | m4 | used once |
+| test_member.cpp:18:9:18:11 | sm1 | Member POD variable 'sm1' in 's1' is only $@. | test_member.cpp:23:6:23:8 | sm1 | used once |
+| test_member.cpp:36:7:36:8 | m1 | Member POD variable 'm1' in 'C' is only $@. | test_member.cpp:39:21:39:22 | m1 | used once |
+| test_member.cpp:37:7:37:8 | m2 | Member POD variable 'm2' in 'C' is only $@. | test_member.cpp:46:5:46:6 | m2 | used once |
+| test_member.cpp:55:5:55:6 | m3 | Member POD variable 'm3' in 'E<B>' is only $@. | test_member.cpp:56:27:56:32 | constructor init of field m3 | used once |

cpp/autosar/test/rules/M0-1-4/test_member.cpp

@@ -72,4 +72,62 @@ void test_e() { // Ensure that the template E is fully instantiated
   e2.getT();
 }
 
+void test_fp_reported_in_388() {
+  struct s1 {
+    int m1; // COMPLIANT
+  };
+
+  s1 l1 = {1}; // m1 is used here
+  l1.m1;
+}
+
+void test_array_initialized_members() {
+  struct s1 {
+    int m1; // COMPLIANT
+  };
+
+  struct s1 l1[] = {
+      {.m1 = 1},
+      {.m1 = 2},
+  };
+
+  l1[0].m1;
+}
+
+void test_indirect_assigned_members(void *opaque) {
+  struct s1 {
+    int m1; // COMPLIANT
+  };
+
+  struct s1 *p = (struct s1 *)opaque;
+  p->m1;
+
+  struct s2 {
+    int m1; // COMPLIANT
+  };
+
+  char buffer[sizeof(struct s2) + 8] = {0};
+  struct s2 *l2 = (struct s2 *)&buffer[8];
+  l2->m1;
+}
+
+void test_external_assigned_members(void (*fp)(unsigned char *)) {
+
+  struct s1 {
+    int m1; // COMPLIANT
+  };
+
+  struct s1 l1;
+  fp((unsigned char *)&l1);
+  l1.m1;
+
+  struct s2 {
+    int m1; // COMPLIANT
+  };
+
+  struct s2 (*copy_init)();
+  struct s2 l2 = copy_init();
+  l2.m1;
+}
+
 } // namespace test