MISRA C rules for Xen

Note

IMPORTANT All MISRA C rules, text, and examples are copyrighted by the MISRA Consortium Limited and used with permission.

Please refer to https://www.misra.org.uk/ to obtain a copy of MISRA C, or for licensing options for other use of the rules.

The following is the list of MISRA C rules that apply to the Xen hypervisor.

It is possible that in specific circumstances it is best not to follow a rule because it is not possible or because the alternative leads to better code quality. Those cases are called "deviations". They are permissible as long as they are documented as an in-code comment using the following format:

/*
 * MISRA_DEV: Rule ID
 * Justification text.
 */

Other documentation mechanisms are work-in-progress.

The existing codebase is not 100% compliant with the rules. Some of the violations are meant to be documented as deviations, while some others should be fixed. Both compliance and documenting deviations on the existing codebase are work-in-progress.

Dir number Severity Summary Notes
Dir 2.1 Required All source files shall compile without any compilation errors
Dir 4.7 Required If a function returns error information then that error information shall be tested
Dir 4.10 Required Precautions shall be taken in order to prevent the contents of a header file being included more than once
Dir 4.14 Required The validity of values received from external sources shall be checked
Rule number Severity Summary Notes
Rule 1.3 Required There shall be no occurrence of undefined or critical unspecified behaviour
Rule 2.6 Advisory A function should not contain unused label declarations
Rule 3.1 Required The character sequences /* and // shall not be used within a comment
Rule 3.2 Required Line-splicing shall not be used in // comments
Rule 4.1 Required Octal and hexadecimal escape sequences shall be terminated
Rule 4.2 Advisory Trigraphs should not be used
Rule 5.1 Required External identifiers shall be distinct The Xen characters limit for identifiers is 40. Public headers (xen/include/public/) are allowed to retain longer identifiers for backward compatibility.
Rule 5.2 Required Identifiers declared in the same scope and name space shall be distinct The Xen characters limit for identifiers is 40. Public headers (xen/include/public/) are allowed to retain longer identifiers for backward compatibility.
Rule 5.3 Required An identifier declared in an inner scope shall not hide an identifier declared in an outer scope Using macros as macro parameters at invocation time is allowed even if both macros use identically named local variables, e.g. max(var0, min(var1, var2))
Rule 5.4 Required Macro identifiers shall be distinct The Xen characters limit for macro identifiers is 40. Public headers (xen/include/public/) are allowed to retain longer identifiers for backward compatibility.
Rule 6.2 Required Single-bit named bit fields shall not be of a signed type
Rule 8.1 Required Types shall be explicitly specified
Rule 8.4 Required A compatible declaration shall be visible when an object or function with external linkage is defined
Rule 8.5 Required An external object or function shall be declared once in one and only one file
Rule 8.6 Required An identifier with external linkage shall have exactly one external definition Declarations without definitions are allowed (specifically when the definition is compiled-out or optimized-out by the compiler)
Rule 8.8 Required The static storage class specifier shall be used in all declarations of objects and functions that have internal linkage
Rule 8.10 Required An inline function shall be declared with the static storage class gnu_inline (without static) is allowed.
Rule 8.12 Required Within an enumerator list the value of an implicitly-specified enumeration constant shall be unique
Rule 9.1 Mandatory The value of an object with automatic storage duration shall not be read before it has been set Rule clarification: do not use variables before they are initialized. An explicit initializer is not necessarily required. Try reducing the scope of the variable. If an explicit initializer is added, consider initializing the variable to a poison value.
Rule 9.2 Required The initializer for an aggregate or union shall be enclosed in braces
Rule 13.6 Mandatory The operand of the sizeof operator shall not contain any expression which has potential side effects
Rule 14.1 Required A loop counter shall not have essentially floating type
Rule 16.7 Required A switch-expression shall not have essentially Boolean type
Rule 17.3 Mandatory A function shall not be declared implicitly
Rule 17.4 Mandatory All exit paths from a function with non-void return type shall have an explicit return statement with an expression
Rule 17.6 Mandatory The declaration of an array parameter shall not contain the static keyword between the [ ]
Rule 19.1 Mandatory An object shall not be assigned or copied to an overlapping object Be aware that the static analysis tool Eclair might report several findings for Rule 19.1 of type "caution". These are instances where Eclair is unable to verify that the code is valid in regard to Rule 19.1. Caution reports are not violations.
Rule 20.7 Required Expressions resulting from the expansion of macro parameters shall be enclosed in parentheses
Rule 20.13 Required A line whose first token is # shall be a valid preprocessing directive
Rule 20.14 Required All #else #elif and #endif preprocessor directives shall reside in the same file as the #if #ifdef or #ifndef directive to which they are related