Remove deceptive uses of AssignBitwiseOperator

AssignBitwiseOperator erroneously includes pointer += and -=.

Author: lcartey

c/misra/src/rules/RULE-10-1/OperandsOfAnInappropriateEssentialType.ql

@@ -14,6 +14,7 @@
 import cpp
 import codingstandards.c.misra
 import codingstandards.c.misra.EssentialTypes
+import codingstandards.cpp.Bitwise
 
 /**
  * Holds if the operator `operator` has an operand `child` that is of an inappropriate essential type
@@ -177,7 +178,7 @@ predicate isInappropriateEssentialType(
     child =
       [
         operator.(BinaryBitwiseOperation).getAnOperand(),
-        operator.(AssignBitwiseOperation).getAnOperand()
+        operator.(AssignBitwiseOperationFixed).getAnOperand()
       ] and
     not operator instanceof LShiftExpr and
     not operator instanceof RShiftExpr and

c/misra/test/rules/RULE-10-1/test.c

@@ -492,4 +492,6 @@ void pointerType() {
   b || b; // COMPLIANT
   p || b; // NON_COMPLIANT
   b || p; // NON_COMPLIANT
+  p+=1; // COMPLIANT
+  p-=1; // COMPLIANT
 }

change_notes/2023-10-04-m5-0-20-exclude-pointer-bitwise.md

@@ -1 +1 @@
- * `M5-0-20` - exclude pointer assignment operators as bitwise operators.
+ * `M5-0-20`, `M5-0-21`, `RULE-10-1` - exclude pointer assignment operators as bitwise operators.

cpp/autosar/src/rules/M5-0-20/BitwiseOperatorOperandsHaveDifferentUnderlyingType.ql

@@ -16,19 +16,14 @@
 
 import cpp
 import codingstandards.cpp.autosar
+import codingstandards.cpp.Bitwise
 
 predicate isBinaryBitwiseOperation(Operation o, VariableAccess l, VariableAccess r) {
   exists(BinaryBitwiseOperation bbo | bbo = o |
     l = bbo.getLeftOperand() and r = bbo.getRightOperand()
   )
   or
-  exists(AssignBitwiseOperation abo |
-    abo = o and
-    // exclude += and -= on pointers, which seem to be erroneously included
-    // in the database schema
-    not abo instanceof AssignPointerAddExpr and
-    not abo instanceof AssignPointerSubExpr
-  |
+  exists(AssignBitwiseOperationFixed abo | abo = o |
     l = abo.getLValue() and
     r = abo.getRValue()
   )

cpp/autosar/src/rules/M5-0-21/BitwiseOperatorAppliedToSignedTypes.ql

@@ -17,14 +17,15 @@
 
 import cpp
 import codingstandards.cpp.autosar
+import codingstandards.cpp.Bitwise
 
 from Operation o, VariableAccess va
 where
   not isExcluded(o, ExpressionsPackage::bitwiseOperatorAppliedToSignedTypesQuery()) and
   (
     o instanceof UnaryBitwiseOperation or
     o instanceof BinaryBitwiseOperation or
-    o instanceof AssignBitwiseOperation
+    o instanceof AssignBitwiseOperationFixed
   ) and
   o.getAnOperand() = va and
   va.getTarget().getUnderlyingType().(IntegralType).isSigned()

cpp/autosar/src/rules/M5-8-1/RightBitShiftOperandIsNegativeOrTooWide.ql

@@ -17,6 +17,7 @@
 
 import cpp
 import codingstandards.cpp.autosar
+import codingstandards.cpp.Bitwise
 
 class ShiftOperation extends Operation {
   Expr leftOperand;
@@ -33,7 +34,7 @@ class ShiftOperation extends Operation {
       rightOperand = o.getRightOperand()
     )
     or
-    exists(AssignBitwiseOperation o | this = o |
+    exists(AssignBitwiseOperationFixed o | this = o |
       (
         o instanceof AssignLShiftExpr
         or

cpp/autosar/test/rules/M5-0-21/test.cpp

@@ -45,4 +45,8 @@ void test() {
   u ^= u;  // COMPLIANT
   u | 0;   // COMPLIANT
   u |= 0;  // COMPLIANT
+
+  int *p = 0;
+  p += 1; // COMPLIANT
+  p -= 1; // COMPLIANT
 }

cpp/common/src/codingstandards/cpp/Bitwise.qll

@@ -0,0 +1,18 @@
+/**
+ * A library for addressing issues in bitwise operator modelling in our database schema.
+ */
+
+import cpp
+
+/**
+ * A binary bitwise assign operation, excluding += and -= on pointers, which seem to be erroneously
+ * included.
+ */
+class AssignBitwiseOperationFixed extends AssignBitwiseOperation {
+  AssignBitwiseOperationFixed() {
+    // exclude += and -= on pointers, which seem to be erroneously included
+    // in the database schema
+    not this instanceof AssignPointerAddExpr and
+    not this instanceof AssignPointerSubExpr
+  }
+}