RULE-12-2

Author: mbaluda

c/misra/src/rules/RULE-12-2/RightHandOperandOfAShiftRange.ql

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+/**
+ * @id c/misra/right-hand-operand-of-a-shift-range
+ * @name RULE-12-2: The right operand of a shift shall be smaller then the width in bits of the left operand
+ * @description The right hand operand of a shift operator shall lie in the range zero to one less
+ *              than the width in bits of the essential type of the left hand operand
+ * @kind problem
+ * @precision very-high
+ * @problem.severity error
+ * @tags external/misra/id/rule-12-2
+ *       correctness
+ *       external/misra/obligation/required
+ */
+
+import cpp
+import codingstandards.c.misra
+import codingstandards.c.misra.EssentialTypes
+import semmle.code.cpp.rangeanalysis.SimpleRangeAnalysis
+
+class ShiftExpr extends BinaryBitwiseOperation {
+  ShiftExpr() { this instanceof LShiftExpr or this instanceof RShiftExpr }
+}
+
+from ShiftExpr e, Expr right, int max_val
+where
+  not isExcluded(right, Contracts7Package::rightHandOperandOfAShiftRangeQuery()) and
+  right = e.getRightOperand().getFullyConverted() and
+  max_val = (8 * getEssentialType(e.getLeftOperand()).getSize()) - 1 and
+  (
+    lowerBound(right) < 0 or
+    upperBound(right) > max_val
+  )
+select right, "The shift right hand operand shall lie in the range 0 to " + max_val + "."

c/misra/test/rules/RULE-12-2/RightHandOperandOfAShiftRange.expected

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+| test.c:8:10:8:10 | 8 | The shift right hand operand shall lie in the range 0 to 7. |
+| test.c:10:10:10:14 | ... + ... | The shift right hand operand shall lie in the range 0 to 7. |
+| test.c:11:10:11:14 | ... + ... | The shift right hand operand shall lie in the range 0 to 7. |
+| test.c:15:9:15:9 | 8 | The shift right hand operand shall lie in the range 0 to 7. |
+| test.c:20:9:20:10 | 64 | The shift right hand operand shall lie in the range 0 to 63. |
+| test.c:23:10:23:11 | 10 | The shift right hand operand shall lie in the range 0 to 7. |
+| test.c:24:10:24:11 | 64 | The shift right hand operand shall lie in the range 0 to 7. |

c/misra/test/rules/RULE-12-2/RightHandOperandOfAShiftRange.qlref

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+rules/RULE-12-2/RightHandOperandOfAShiftRange.ql

c/misra/test/rules/RULE-12-2/test.c

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+#include <stdint.h>
+
+void f1() {
+  uint8_t ui8;
+  int b = 4;
+
+  ui8 << 7;            // COMPLIANT
+  ui8 >> 8;            // NON_COMPLIANT
+  ui8 << 3 + 3;        // COMPLIANT
+  ui8 >> 4 + b;        // NON_COMPLIANT
+  ui8 << b + b;        // NON_COMPLIANT
+  (uint16_t) ui8 << 9; // COMPLIANT
+
+  // 0u essential type is essentially unsigned char
+  0u << 8;           // NON_COMPLIANT
+  (uint16_t)0u << 8; // COMPLIANT
+
+  unsigned long ul;
+  ul << 10; // COMPLIANT
+  ul << 64; // NON_COMPLIANT
+
+  // 1UL essential type is essentially unsigned long
+  1UL << 10; // COMPLIANT(FALSE_POSITIVE)
+  1UL << 64; // NON_COMPLIANT
+}