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This issue is similar to the signedness of plain char, discussed in INT07-C. Use only explicitly signed or unsigned char type for numeric values. A plain int bit-field that is treated as unsigned will promote to int as long as its field width is less than that of int because int can hold all values of the original type. This behavior is the same behavior as that of a plain char treated as unsigned. However, a plain int bit-field treated as unsigned will promote to unsigned int if its field width is the same as that of int. This difference makes a plain int bit-field even trickier than a plain char.
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Making invalid assumptions about the type of a bit-field or its layout can result in unexpected program flow.
Recommendation | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
INT12-C |
Low |
Unlikely |
Medium | P2 | L3 |
Automated Detection
Tool | Version | Checker | Description | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Astrée |
| bitfield-type | Fully checked | ||||||
| Axivion Bauhaus Suite |
| CertC-INT12 | |||||||
| CodeSonar |
| LANG.TYPE.BFSIGN | Bit-field signedness not explicit | ||||||
| Compass/ROSE |
| CC2.INT12 | Fully implemented | |||||||
| Helix QAC |
| C0634, C0635 | |||||||
| Klocwork |
| MISRA.BITFIELD.TYPE | |||||||
| LDRA tool suite |
| 73 S | Fully implemented |
| Parasoft C/C++test |
| CERT_C-INT12-a | Bit fields shall only be defined to be of type unsigned int or signed int | ||||||
| PC-lint Plus |
| 846 | Fully supported | ||||||
| Polyspace Bug Finder |
| Checks for bit-field declared without appropriate type (rec. fully covered) | |||||||
| RuleChecker |
| bitfield-type | Fully checked | ||||||
| SonarQube C/C++ Plugin |
| S814 |
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
Related Guidelines
| SEI CERT C++ |
| Coding Standard | VOID INT12-CPP. Do not make assumptions about the type of a plain int bit-field when used in an expression |
| ISO/IEC TR 24772:2013 | Bit Representations [STR] |
| MISRA C:2012 | Rule 10.1 (required) |
Bibliography
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