정적검증 시 MISRA C 가이드라인이란? #임베디드 자동차 모델 기반 코딩 규칙

MISRA C의 등장 배경

Misra C의 등장 배경은 C 언어를 사용하는 소프트웨어 개발에서 발생하는 여러 문제를 해결하기 위해 만들어졌다.

C언어는 강력하고 유연한 언어지만, 잘못 사용할 경우 코드의 안전성, 보안성, 이식성 등에 문제가 발생할 수 있다.

특히, 안전 관련 산업 분야에서는 이러한 문제가 치명적일 수 있다.

 

Misra C의 등장 배경에는 다음과 같은 이유들이 있다:
1. 소프트웨어 신뢰성 요구 증가
산업 분야에서 사용되는 소프트웨어의 신뢰성 요구가 증가하면서, 안전하고 신뢰할 수 있는 코드를 작성하기 위한 필요성이 대두되었다.
2. C 언어의 유연성과 위험성
C언어는 매우 유연한 언어이지만, 잘못 사용할 경우 버그, 보안 취약점, 메모리 오류 등이 발생할 수 있다.
3. 산업 안전 요구 사항의 증가
산업 분야에서는 안전 요구 사항이 매우 엄격하며, 이를 충족시키기 위해서는 안전한 코드 작성이 필수적이다.
4. 소프트웨어의 복잡성 증가
현대 소프트웨어는 매우 복잡해지고 있으며, 이에 따라 코드의 신뢰성을 유지하기 위한 가이드라인이 필요해졌다.

Misra C는 이러한 배경 아래서 C 언어를 사용하는 소프트웨어 개발에서 발생하는 문제들을 해결하고, 안전하고 신뢰할 수 있는 코드를 작성하기 위한 목적으로 개발되었다. Misra C의 규칙들은 이러한 목표를 달성하기 위해 안전한 코딩 스타일을 제시하고, 코드의 신뢰성을 향상시키는데 도움을 준다.

 

 

MISRA C 가이드라인 규칙

모든 MISRA C 가이드라인은 " Mandatory ", " Required ", " Advisory "이라는 단일 범주를 가지며 아래와 같다.

• Mandatory Rule - 어길 수 없는 가이드라인으로, 필수로 지켜야한다. 즉, 어떠한 예외도 허용하지 않는다.
• Required Rule - 명확한 제약 조건, 요구 사항 및 주의 사항을 정의하는 예외를 지원할 때만 어길 수 있는 가이드라인으로, 정당한 사유가 있을 경우에 한해서 예외가 허용된다.
• Advisory Rule - 합리적으로 준수될 수 있는 권고 사항으로, 가이드라인 규칙을 어길 수는 있지만 반드시 지켜야 할 필요는 없다.

 

MISRA C 예시 (Rule 20.2)

만약 이러한 코드로 예를 들어보자.

#include "fi'le.h"    /* Non-compliant */

 

누가봐도 코드가 이상하지 않는가. 제일 쉬는 놈으로다가 예로 들었다.

이를 QAC 와 같은 정적검증 Tool 을 이용하여 검사해보면 MISRA C Rule에 아래와 같이 검출될 것이다.

 

이 규칙은 20.2 에 해당하며 해석하면 다음과 같다.

헤더 파일 이름에 ', ", 또는 \ 문자 및 /* 또는 // 문자열이 포함되어서는 안된다.

말 그대로 ' 가 들어가 있지 않은가. 

', ", 또는 \ 문자 또는 /* 또는 // 문자열이 사용되어 위와 같은 Rule 위반 메시지가 검출될 것이다. 

 

 

MISRA C 코딩 Rule 

아래는 MISRA C 2012 Guidelines for the use of.pdf 에 있는 내용을 첨삭하여 일부 내용을 가져왔다.

 

A standard C environment
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
Rule 1.2 Advisory Language extensions should not be used
Rule 1.3 Required There shall be no occurrence of undefined or critical unspecified behaviour

 

Unused code
Rule 2.1 Required A project shall not contain unreachable code
Rule 2.2 Required There shall be no dead code
Rule 2.3 Advisory A project should not contain unused type declarations
Rule 2.4 Advisory A project should not contain unused tag declarations
Rule 2.5 Advisory A project should not contain unused macro declarations
Rule 2.6 Advisory A function should not contain unused label declarations
Rule 2.7 Advisory There should be no unused parameters in functions

 

Comments
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

 

Character sets and lexical conventions
Rule 4.1 Required Octal and hexadecimal escape sequences shall be terminated
Rule 4.2 Advisory Trigraph should not be used

 

Identifiers
Rule 5.1 Required External identifiers shall be distinct
Rule 5.2 Required Identifiers declared in the same scope and name space shall be distinct
Rule 5.3 Required An identifier declared in an inner scope shall not hide an identifier declared in an outer scope
Rule 5.4 Required Macro identifiers shall be distinct
Rule 5.5 Required Identifiers shall be distinct from macro names
Rule 5.6 Required A type def name shall be a unique identifier
Rule 5.7 Required A tag name shall be a unique identifier
Rule 5.8 Required Identifiers that Defi ne objects or functions with external linkage shall be unique
Rule 5.9 Advisory Identifiers that Defi ne objects or functions with internal linkage should be unique

Types
Rule 6.1 Required Bit-FI LEDS shall only be declared with an appropriate type
Rule 6.2 Required Single-bit named bit FI LEDS shall not be of a signed type

Literals and constants
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
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’s type is “pointer to cons-qualified char”

Declarations and Defi nit ions
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 Defi Ned
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
Rule 8.7 Advisory Functions and objects should not be Defi Ned with external linkage if they are referenced in only one translation unit
Rule 8.8 Required The static storage class specifier shall be used in all declarations of objects and functions that have internal linkage
Rule 8.9 Advisory An object should be Defi Ned at block scope if its identifier only appears in a single function
Rule 8.10 Required An inline function shall be declared with the static storage class
Rule 8.11 Advisory When an array with external linkage is declared, its size should be explicitly specified

Rule 8.12 Required Within an enumerator list, the value of an implicitly-specified enumeration constant shall be unique
Rule 8.13 Advisory A pointer should point to a const-qualifi ed type whenever possible
Rule 8.14 Required The restrict type qualifi er shall not be used

Initialization
Rule 9.1 Mandatory The value of an object with automatic storage duration shall not be read before it has been set
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
Rule 9.4 Required An element of an object shall not be initialized more than once
Rule 9.5 Required Where designated initializers are used to initialize an array object the size of the array shall be specifi ed explicitly

The essential type model
Rule 10.1 Required Operands shall not be of an inappropriate essential type
Rule 10.2 Required Expressions of essentially character type shall not be used inappropriately in addition and subtraction operations
Rule 10.3 Required The value of an expression shall not be assigned to an object with a narrower essential type or of a diff erent essential type category
Rule 10.4 Required Both operands of an operator in which the usual arithmetic conversions are performed shall have the same essential type category
Rule 10.5 Advisory The value of an expression should not be cast to an inappropriate essential type
Rule 10.6 Required The value of a composite expression shall not be assigned to an object with wider essential type
Rule 10.7 Required If a composite expression is used as one operand of an operator in which the usual arithmetic conversions are performed then the other operand shall not have wider essential type
Rule 10.8 Required The value of a composite expression shall not be cast to a diff erent essential type category or a wider essential type

Pointer type conversions
Rule 11.1 Required Conversions shall not be performed between a pointer to a function and any other type
Rule 11.2 Required Conversions shall not be performed between a pointer to an incomplete type and any other type
Rule 11.3 Required A cast shall not be performed between a pointer to object type and a pointer to a diff erent object type
Rule 11.4 Advisory A conversion should not be performed between a pointer to object and an integer type
Rule 11.5 Advisory A conversion should not be performed from pointer to void into pointer to object
Rule 11.6 Required A cast shall not be performed between pointer to void and an arithmetic type
Rule 11.7 Required A cast shall not be performed between pointer to object and a noninteger arithmetic type
Rule 11.8 Required A cast shall not remove any const or volatile qualifi cation from the type pointed to by a pointer
Rule 11.9 Required The macro NULL shall be the only permitted form of integer null pointer constant

 

Expressions
Rule 12.1 Advisory The precedence of operators within expressions should be made explicit
Rule 12.2 Required The right hand operand of a shift operator shall lie in the range zero to one less than the width in bits of the essential type of the left hand operand
Rule 12.3 Advisory The comma operator should not be used
Rule 12.4 Advisory Evaluation of constant expressions should not lead to unsigned integer wrap-around

Side effects
Rule 13.1 Required Initializer lists shall not contain persistent side eff ects
Rule 13.2 Required The value of an expression and its persistent side eff ects shall be the same under all permitted evaluation orders
Rule 13.3 Advisory A full expression containing an increment (++) or decrement (--) operator should have no other potential side eff ects other than that caused by the increment or decrement operator
Rule 13.4 Advisory The result of an assignment operator should not be used
Rule 13.5 Required The right hand operand of a logical && or || operator shall not contain persistent side eff ects
Rule 13.6 Mandatory The operand of the sizeof operator shall not contain any expression which has potential side eff ects

Control statement expressions
Rule 14.1 Required A loop counter shall not have essentially fl oating type
Rule 14.2 Required A for loop shall be well-formed
Rule 14.3 Required Controlling expressions shall not be invariant
Rule 14.4 Required The controlling expression of an if statement and the controlling expression of an iteration-statement shall have essentially Boolean type

Control fl ow
Rule 15.1 Advisory The goto statement should not be used
Rule 15.2 Required The goto statement shall jump to a label declared later in the same function
Rule 15.3 Required Any label referenced by a goto statement shall be declared in the same block, or in any block enclosing the goto statement
Rule 15.4 Advisory There should be no more than one break or goto statement used to terminate any iteration statement
Rule 15.5 Advisory A function should have a single point of exit at the end
Rule 15.6 Required The body of an iteration-statement or a selection-statement shall be a compound-statement
Rule 15.7 Required All if … else if constructs shall be terminated with an else statement

Switch statements
Rule 16.1 Required All switch statements shall be well-formed
Rule 16.2 Required A switch label shall only be used when the most closely-enclosing compound statement is the body of a switch statement
Rule 16.3 Required An unconditional break statement shall terminate every switch-clause
Rule 16.4 Required Every switch statement shall have a default label
Rule 16.5 Required A default label shall appear as either the fi rst or the last switch label of a switch statement
Rule 16.6 Required Every switch statement shall have at least two switch-clauses
Rule 16.7 Required A switch-expression shall not have essentially Boolean type

Functions
Rule 17.1 Required The features of <stdarg.h> shall not be used
Rule 17.2 Required Functions shall not call themselves, either directly or indirectly
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 17.5 Advisory The function argument corresponding to a parameter declared to have an array type shall have an appropriate number of elements
Rule 17.6 Mandatory The declaration of an array parameter shall not contain the static keyword between the [ ]
Rule 17.7 Required The value returned by a function having non-void return type shall be used
Rule 17.8 Advisory A function parameter should not be modifi ed

Pointers and arrays
Rule 18.1 Required A pointer resulting from arithmetic on a pointer operand shall address an element of the same array as that pointer operand
Rule 18.2 Required Subtraction between pointers shall only be applied to pointers that address elements of the same array
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 18.4 Advisory The +, -, += and -= operators should not be applied to an expression of pointer type
Rule 18.5 Advisory Declarations should contain no more than two levels of pointer nesting
Rule 18.6 Required The address of an object with automatic storage shall not be copied to another object that persists after the fi rst object has ceased to exist
Rule 18.7 Required Flexible array members shall not be declared
Rule 18.8 Required Variable-length array types shall not be used

Overlapping storage
Rule 19.1 Mandatory An object shall not be assigned or copied to an overlapping object
Rule 19.2 Advisory The union keyword should not be used

Preprocessing directives
Rule 20.1 Advisory #include directives should only be preceded by preprocessor directives or comments
Rule 20.2 Required The ', " or \ characters and the /* or // character sequences shall not occur in a header fi le name
Rule 20.3 Required The #include directive shall be followed by either a <filename> or "filename" sequence
Rule 20.4 Required A macro shall not be defi ned with the same name as a keyword
Rule 20.5 Advisory #undef should not be used
Rule 20.6 Required Tokens that look like a preprocessing directive shall not occur within a macro argument
Rule 20.7 Required Expressions resulting from the expansion of macro parameters shall be enclosed in parentheses
Rule 20.8 Required The controlling expression of a #if or #elif preprocessing directive shall evaluate to 0 or 1
Rule 20.9 Required All identifi ers used in the controlling expression of #if or #elif preprocessing directives shall be #defi ne’d before evaluation
Rule 20.10 Advisory The # and ## preprocessor operators should not be used
Rule 20.11 Required A macro parameter immediately following a # operator shall not immediately be followed by a ## operator
Rule 20.12 Required A macro parameter used as an operand to the # or ## operators, which is itself subject to further macro replacement, shall only be used as an operand to these operators
Rule 20.13 Required A line whose fi rst token is # shall be a valid preprocessing directive
Rule 20.14 Required All #else, #elif and #endif preprocessor directives shall reside in the same fi le as the #if, #ifdef or #ifndef directive to which they are related

Standard libraries
Rule 21.1 Required #defi ne and #undef shall not be used on a reserved identifi er or reserved macro name
Rule 21.2 Required A reserved identifi er or macro name shall not be declared
Rule 21.3 Required The memory allocation and deallocation functions of <stdlib.h> shall not be used
Rule 21.4 Required The standard header fi le <setjmp.h> shall not be used
Rule 21.5 Required The standard header fi le <signal.h> shall not be used
Rule 21.6 Required The Standard Library input/output functions shall not be used
Rule 21.7 Required The atof, atoi, atol and atoll functions of <stdlib.h> shall not be used
Rule 21.8 Required The library functions abort, exit, getenv and system of <stdlib.h> shall not be used
Rule 21.9 Required The library functions bsearch and qsort of <stdlib.h> shall not be used
Rule 21.10 Required The Standard Library time and date functions shall not be used
Rule 21.11 Required The standard header fi le <tgmath.h> shall not be used
Rule 21.12 Advisory The exception handling features of <fenv.h> should not be used

Resources
Rule 22.1 Required All resources obtained dynamically by means of Standard Library functions shall be explicitly released
Rule 22.2 Mandatory A block of memory shall only be freed if it was allocated by means of a Standard Library function
Rule 22.3 Required The same fi le shall not be open for read and write access at the same time on diff erent streams
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