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 3.2	Required	Line-splicing shall not be used in // comments
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 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