CERT C: Rec. MSC15-C

Do not depend on undefined behavior

expand all in page

Description

Rule Definition

Do not depend on undefined behavior.¹

Polyspace Implementation

The rule checker checks for Undefined behavior.

Examples

expand all

Undefined behavior

Issue

The issue occurs when the analysis detects undefined or critical unspecified behaviour. Specifically, Polyspace^® flags these instances of undefined or critical undefined behavior:

Use of offsetof on bit fields.
Use of offsetof when the second argument is not a struct field of the first argument.
Use of defined without an identifier.
Use of an array of incomplete types.
Use of a function like macros by using incorrect number of arguments.

Risk

C code that results in undefined or critical unspecified behavior might produce unexpected or incorrect results. Such code might behave differently in different implementations. Issues caused by undefined behavior in the code might be difficult to analyze because compilers might optimize the code assuming that undefined behavior does not occur.

Fix

Avoid code that might result in undefined or critically unspecified behavior.

Example — Avoid Undefined Behaviors

#include <stddef.h>     /* offsetof */

struct str {
  char a:8;
  char b[10];
  char c;
};
void foo() {
  
  offsetof(struct str, a);//Noncompliant
  offsetof(struct str, d);//Noncompliant
}

In this example, the function foo uses the macro offsetof on the bit field str.a. This behavior is undefined. Polyspace flags it. The function then calls offsetof on str.d. Because d is not a field of str, Polyspace flags it.

These issues might cause compilation errors with your compiler. Polyspace flags this issue as a rule violation while also showing a compilation failure.

Check Information

Group: Rec. 48. Miscellaneous (MSC)

Version History

Introduced in R2019a

¹ This software has been created by MathWorks incorporating portions of: the “SEI CERT-C Website,” © 2017 Carnegie Mellon University, the SEI CERT-C++ Web site © 2017 Carnegie Mellon University, ”SEI CERT C Coding Standard – Rules for Developing safe, Reliable and Secure systems – 2016 Edition,” © 2016 Carnegie Mellon University, and “SEI CERT C++ Coding Standard – Rules for Developing safe, Reliable and Secure systems in C++ – 2016 Edition” © 2016 Carnegie Mellon University, with special permission from its Software Engineering Institute.

ANY MATERIAL OF CARNEGIE MELLON UNIVERSITY AND/OR ITS SOFTWARE ENGINEERING INSTITUTE CONTAINED HEREIN IS FURNISHED ON AN "AS-IS" BASIS. CARNEGIE MELLON UNIVERSITY MAKES NO WARRANTIES OF ANY KIND, EITHER EXPRESSED OR IMPLIED, AS TO ANY MATTER INCLUDING, BUT NOT LIMITED TO, WARRANTY OF FITNESS FOR PURPOSE OR MERCHANTABILITY, EXCLUSIVITY, OR RESULTS OBTAINED FROM USE OF THE MATERIAL. CARNEGIE MELLON UNIVERSITY DOES NOT MAKE ANY WARRANTY OF ANY KIND WITH RESPECT TO FREEDOM FROM PATENT, TRADEMARK, OR COPYRIGHT INFRINGEMENT.

This software and associated documentation has not been reviewed nor is it endorsed by Carnegie Mellon University or its Software Engineering Institute.