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. For details, please refer to docs/misra/documenting-violations.rst
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.
The list below might need to be updated over time. Reach out to THE REST maintainers if you want to suggest a change.
| Dir number | Severity | Summary | Notes |
|---|---|---|---|
| Dir 1.1 | Required | Any implementation-defined behaviour on which the output of the program depends shall be documented and understood | |
| 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 4.11 | Required | The validity of values passed to library functions shall be checked | We do not have libraries in Xen (libfdt and others are not considered libraries from MISRA C point of view as they are imported in source form) |
| Dir 4.14 | Required | The validity of values received from external sources shall be checked |
| Rule number | Severity | Summary | Notes |
|---|---|---|---|
| Rule 1.1 | Required | The program shall contain no violations of the standard C syntax and constraints, and shall not exceed the implementation’s translation limits | We make use of several compiler extensions as documented by C-language-toolchain.rst |
| Rule 1.3 | Required | There shall be no occurrence of undefined or critical unspecified behaviour | |
| Rule 1.4 | Required | Emergent language features shall not be used | Emergent language features, such as C11 features, should not be confused with similar compiler extensions, which we use. When the time comes to adopt C11, this rule will be revisited. |
| Rule 2.1 | Required | A project shall not contain unreachable code | |
| 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 5.6 | Required | A typedef name shall be a unique identifier | |
| Rule 6.1 | Required | Bit-fields shall only be declared with an appropriate type | In addition to the C99 types, we also consider appropriate types enum and all explicitly signed / unsigned integer types. |
| Rule 6.2 | Required | Single-bit named bit fields shall not be of a signed type | |
| Rule 7.1 | Required | Octal constants shall not be used | |
| Rule 7.2 | Required | A “u” or “U” suffix shall be applied to all integer constants that are represented in an unsigned type | The rule asks that any integer literal that is implicitly unsigned is made explicitly unsigned by using one of the indicated suffixes. As an example, on a machine where the int type is 32-bit wide, 0x77777777 is signed whereas 0x80000000 is (implicitly) unsigned. In order to comply with the rule, the latter should be rewritten as either 0x80000000u or 0x80000000U. Consistency considerations may suggest using the same suffix even when not required by the rule. For instance, if one has: Original: f(0x77777777); f(0x80000000); one should do Solution 1: f(0x77777777U); f(0x80000000U); over Solution 2: f(0x77777777); f(0x80000000U); after having ascertained that “Solution 1” is compatible with the intended semantics. |
| Rule 7.3 | Required | The lowercase character l shall not be used in a literal suffix | |
| Rule 7.4 | Required | A string literal shall not be assigned to an object unless the object type is pointer to const-qualified char | All “character types” are permitted, as long as the string element type and the character type match. (There should be no casts.) Assigning a string literal to any object with type “pointer to const-qualified void” is allowed. |
| Rule 8.1 | Required | Types shall be explicitly specified | |
| Rule 8.2 | Required | Function types shall be in prototype form with named parameters | |
| Rule 8.3 | Required | All declarations of an object or function shall use the same names and type qualifiers | |
| 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 8.14 | Required | The restrict type qualifier shall not be used | |
| 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 9.3 | Required | Arrays shall not be partially initialized | {} is also allowed to specify explicit zero-initialization |
| Rule 9.4 | Required | An element of an object shall not be initialized more than once | |
| Rule 12.5 | Mandatory | The sizeof operator shall not have an operand which is a function parameter declared as “array of type” | |
| Rule 13.6 | Mandatory | The operand of the sizeof operator shall not contain any expression which has potential side effects | |
| Rule 13.1 | Required | Initializer lists shall not contain persistent 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 18.3 | Required | The relational operators > >= < and <= shall not be applied to objects of pointer type except where they point into the same object | |
| 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 | |
| Rule 21.13 | Mandatory | Any value passed to a function in <ctype.h> shall be representable as an unsigned char or be the value EOF | |
| Rule 21.17 | Mandatory | Use of the string handling functions from <string.h> shall not result in accesses beyond the bounds of the objects referenced by their pointer parameters | |
| Rule 21.18 | Mandatory | The size_t argument passed to any function in <string.h> shall have an appropriate value | |
| Rule 21.19 | Mandatory | The pointers returned by the Standard Library functions localeconv, getenv, setlocale or, strerror shall only be used as if they have pointer to const-qualified type | |
| Rule 21.20 | Mandatory | The pointer returned by the Standard Library functions asctime ctime gmtime localtime localeconv getenv setlocale or strerror shall not be used following a subsequent call to the same function | |
| Rule 21.21 | Required | The Standard Library function system of <stdlib.h> shall not be used | |
| Rule 22.2 | Mandatory | A block of memory shall only be freed if it was allocated by means of a Standard Library function | |
| Rule 22.4 | Mandatory | There shall be no attempt to write to a stream which has been opened as read-only | |
| Rule 22.5 | Mandatory | A pointer to a FILE object shall not be dereferenced | |
| Rule 22.6 | Mandatory | The value of a pointer to a FILE shall not be used after the associated stream has been closed |