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CERT C++: MSC53-CPP

Do not return from a function declared [[noreturn]]

Since R2020b

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Description

Rule Definition

Do not return from a function declared [[noreturn]]1

Polyspace Implementation

The rule checker checks for [[noreturn]] functions returning to caller.

Examples

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Issue

This defect occurs when a [[noreturn]] function eventually returns the flow of execution to the caller function. The compiler expects that a function declared by using the [[noreturn]] attribute does not return the flow of execution. That is, if a [[noreturn]] function f() is called from main(), then the compiler expects that the flow of execution is not returned to main(). If such a function eventually returns the flow of execution, it leads to undefined behavior.

Risk

If a [[noreturn]] function eventually returns the flow of execution, it leads to undefined behavior, which can be exploited to cause data integrity violations.

Fix

If a function has no return statement, then the final closing brace of a function implies an implicit return. Omitting a return statement in the function does not prevent the flow of execution from returning. A [[noreturn]] function can prohibit returning the flow of execution to the calling function by:

  • Entering an infinite loop

  • Raising an exception

  • Calling another [[noreturn]] function

Example

Consider the following code containing the function noncompliant(), which is declared as [[noreturn]].

#include <cstdlib>
[[noreturn]] void bad_f(int i)
{
	if (i > 0)
	throw "Received positive input";
	else if (i < 0)
	std::exit(0);
} //Noncompliant

When the input i is zero, the flow of execution skips the if-else-if block of code and returns to the caller implicitly. Because the [[noreturn]] function returns the flow of execution in a code path, this function is noncompliant with this rule.

Correction

A [[noreturn]] function must not return the flow of execution in a code path. You can prevent returning in several ways. Consider the following code where the [[noreturn]] function does not return the flow of execution in a code path.

#include <cstdlib>
[[noreturn]] void compliant(int i)
{
	if (i > 0)
	throw "Received positive input";
	else if (i < 0)
	std::exit(0);
	else if(i==0)
	while(true){
		//...
	}
}//Compliant

This function is compliant with this rule because:

  • When i > 0, the function raises an exception.

  • When i < 0, the function calls the [[noreturn]] function std::exit().

  • When i==0, the function enters an infinite loop.

Because the [[noreturn]] function does not return the flow of execution in a call path, it is compliant with this rule.

Check Information

Group: 49. Miscellaneous (MSC)

Version History

Introduced in R2020b

See Also

Topics

External Websites

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.

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