An object that has volatile-qualified type may be modified in ways unknown to the implementation or have other unknown side effects. It is possible to reference a volatile object by using a non-volatile value, but the resulting behavior is undefined. According to ISO/IEC 9899:1999, Section 6.7.3 "Type Qualifiers" (see also undefined behavior 62 of Appendix J):
If an attempt is made to refer to an object defined with a volatile-qualified type through use of an lvalue with non-volatile-qualified type, the behavior is undefined.
(See also undefined behavior 62 of Appendix J.)
Noncompliant Code Example
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This example compiles without warning on Microsoft Visual C++ .NET (2003) and on MS Visual Studio 2005.
This example does not compile on MS Visual Studio 2008. The error message is
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In this compliant solution, ip is declared as volatile.
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static volatile int **ipp;
static volatile int *ip;
static volatile int i = 0;
printf("i = %d.\n", i);
ipp = &ip;
*ipp = &i;
if (*ip != 0) {
/* ... */
}
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Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
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EXP32-C | low | likely | medium | P6 | L2 |
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Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
Other Languages
Related Guidelines
This rule appears in the C++ Secure Coding Standard as : EXP32-CPP. Do not access a volatile object through a non-volatile reference.
Bibliography
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\[[ISO/IEC 9899:1999|AA. Bibliography#ISO/IEC 9899-1999]\] Section 6.7.3, "Type qualifiers," and Section 6.5.16.1, "Simple assignment" \[[ISO/IEC PDTR 24772|AA. Bibliography#ISO/IEC PDTR 24772]\] "HFC Pointer casting and pointer type changes" and "IHN Type system" \[[MISRA 042004|AA. Bibliography#MISRA 04]\] Rule 11.5 |
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