.. SPDX-License-Identifier: CC-BY-4.0
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 and docs/misra/deviations.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.
.. list-table::
:header-rows: 1
* - Dir number
- Severity
- Summary
- Notes
* - `Dir 1.1 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/D_01_01.c>`_
- Required
- Any implementation-defined behaviour on which the output of the
program depends shall be documented and understood
-
* - `Dir 2.1 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/D_02_01.c>`_
- Required
- All source files shall compile without any compilation errors
-
* - `Dir 4.1 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/D_04_01.c>`_
- Required
- Run-time failures shall be minimized
- The strategies adopted by Xen to prevent certain classes of runtime
failures is documented by
`C-runtime-failures.rst <docs/misra/C-runtime-failures.rst>`_
* - `Dir 4.7 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/D_04_07.c>`_
- Required
- If a function returns error information then that error
information shall be tested
-
* - `Dir 4.10 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/D_04_10.c>`_
- Required
- Precautions shall be taken in order to prevent the contents of a
header file being included more than once
- Files that are intended to be included more than once do not need to
conform to the directive
* - `Dir 4.11 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/D_04_11.c>`_
- 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 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/D_04_14.c>`_
- Required
- The validity of values received from external sources shall be
checked
-
.. list-table::
:header-rows: 1
* - Rule number
- Severity
- Summary
- Notes
* - `Rule 1.1 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_01_01.c>`_
- 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 <docs/misra/C-language-toolchain.rst>`_
* - `Rule 1.3 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_01_03.c>`_
- Required
- There shall be no occurrence of undefined or critical unspecified
behaviour
-
* - `Rule 1.4 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/>`_
- 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 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_02_01_1.c>`_
- Required
- A project shall not contain unreachable code
- The following are allowed:
- Invariantly constant conditions, e.g. if(IS_ENABLED(CONFIG_HVM)) { S; }
- Switch with a controlling value statically determined not to
match one or more case statements
- Functions that are intended to be referenced only from
assembly code (e.g. 'do_trap_fiq')
- asm-offsets.c, as they are not linked deliberately, because
they are used to generate definitions for asm modules
- Declarations without initializer are safe, as they are not
executed
* - `Rule 2.6 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_02_06.c>`_
- Advisory
- A function should not contain unused label declarations
-
* - `Rule 3.1 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_03_01.c>`_
- Required
- The character sequences /* and // shall not be used within a
comment
- Comments containing hyperlinks inside C-style block comments are safe
* - `Rule 3.2 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_03_02.c>`_
- Required
- Line-splicing shall not be used in // comments
-
* - `Rule 4.1 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_04_01.c>`_
- Required
- Octal and hexadecimal escape sequences shall be terminated
-
* - `Rule 4.2 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_04_02.c>`_
- Advisory
- Trigraphs should not be used
-
* - `Rule 5.1 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_05_01_2.c>`_
- 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 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_05_02.c>`_
- 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 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_05_03.c>`_
- 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 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_05_04.c>`_
- 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 5.5 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_05_05.c>`_
- Required
- Identifiers shall be distinct from macro names
- Macros expanding to their own name are allowed, e.g.::
#define x x
Clashes between names of function-like macros and identifiers of
non-callable entities are allowed. Callable entities having an
identifier that is the same of the name of a
function-like macro are not allowed. Example (not allowed)::
#define f(x, y) f(x, y)
void f(int x, int y);
* - `Rule 5.6 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_05_06.c>`_
- Required
- A typedef name shall be a unique identifier
-
* - `Rule 6.1 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_06_01.c>`_
- 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 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_06_02.c>`_
- Required
- Single-bit named bit fields shall not be of a signed type
-
* - `Rule 7.1 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_07_01.c>`_
- Required
- Octal constants shall not be used
-
* - `Rule 7.2 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_07_02.c>`_
- 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 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_07_03.c>`_
- Required
- The lowercase character l shall not be used in a literal suffix
-
* - `Rule 7.4 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_07_04.c>`_
- 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 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_08_01.c>`_
- Required
- Types shall be explicitly specified
-
* - `Rule 8.2 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_08_02.c>`_
- Required
- Function types shall be in prototype form with named parameters
- Clarification: both function and function pointers types shall
have named parameters.
* - `Rule 8.3 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_08_03.c>`_
- Required
- All declarations of an object or function shall use the same
names and type qualifiers
- The type ret_t maybe be deliberately used and defined as int or
long depending on the type of guest to service
* - `Rule 8.4 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_08_04.c>`_
- Required
- A compatible declaration shall be visible when an object or
function with external linkage is defined
- Allowed exceptions: asm-offsets.c, definitions for asm modules
not called from C code, gcov_base.c
* - `Rule 8.5 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_08_05_2.c>`_
- Required
- An external object or function shall be declared once in one and only one file
-
* - `Rule 8.6 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_08_06_2.c>`_
- 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 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_08_08.c>`_
- Required
- The static storage class specifier shall be used in all
declarations of objects and functions that have internal linkage
-
* - `Rule 8.10 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_08_10.c>`_
- Required
- An inline function shall be declared with the static storage class
- gnu_inline (without static) is allowed.
* - `Rule 8.12 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_08_12.c>`_
- Required
- Within an enumerator list the value of an implicitly-specified
enumeration constant shall be unique
-
* - `Rule 8.14 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_08_14.c>`_
- Required
- The restrict type qualifier shall not be used
-
* - `Rule 9.1 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_09_01.c>`_
- 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 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_09_02.c>`_
- Required
- The initializer for an aggregate or union shall be enclosed in
braces
-
* - `Rule 9.3 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_09_03.c>`_
- Required
- Arrays shall not be partially initialized
- {} is also allowed to specify explicit zero-initialization
* - `Rule 9.4 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_09_04.c>`_
- Required
- An element of an object shall not be initialized more than once
-
* - `Rule 10.1 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_10_01.c>`_
- Required
- Operands shall not be of an inappropriate essential type
- The following are allowed:
- Value-preserving conversions of integer constants
- Bitwise and, or, xor, one's complement, bitwise and assignment,
bitwise or assignment, bitwise xor assignment (bitwise and, or, xor
are safe on non-negative integers; also Xen assumes two's complement
representation)
- Left shift, right shift, left shift assignment, right shift
assignment (see C-language-toolchain.rst for uses of
compilers' extensions)
- Implicit conversions to boolean for conditionals (?: if while
for) and logical operators (! || &&)
- The essential type model allows the constants defined by anonymous
enums (e.g., enum { A, B, C }) to be used as operands to arithmetic
operators, as they have a signed essential type.
* - `Rule 10.2 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_10_02.c>`_
- Required
- Expressions of essentially character type shall not be used
inappropriately in addition and subtraction operations
-
* - `Rule 10.3 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_10_03.c>`_
- Required
- The value of an expression shall not be assigned to an object
with a narrower essential type or of a different essential type
category
- Please beware that this rule has many violations in the Xen
codebase today, and its adoption is aspirational. However, when
submitting new patches please try to decrease the number of
violations when possible.
gcc has a helpful warning that can help you spot and remove
violations of this kind: conversion. For instance, you can use
it as follows:
CFLAGS="-Wconversion -Wno-error=sign-conversion -Wno-error=conversion" make -C xen
* - `Rule 10.4 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_10_04.c>`_
- Required
- Both operands of an operator in which the usual arithmetic
conversions are performed shall have the same essential type
category
- Please beware that this rule has many violations in the Xen
codebase today, and its adoption is aspirational. However, when
submitting new patches please try to decrease the number of
violations when possible.
gcc has a helpful warning that can help you spot and remove
violations of this kind: arith-conversion. For instance, you
can use it as follows:
CFLAGS="-Warith-conversion -Wno-error=arith-conversion" make -C xen
* - `Rule 11.1 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_11_01.c>`_
- Required
- Conversions shall not be performed between a pointer to a
function and any other type
- All conversions to integer types are permitted if the destination
type has enough bits to hold the entire value. Conversions to
bool and void* are permitted.
* - `Rule 11.2 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_11_02.c>`_
- Required
- Conversions shall not be performed between a pointer to an
incomplete type and any other type
- All conversions to integer types are permitted if the destination
type has enough bits to hold the entire value. Conversions to
bool and void* are permitted.
* - `Rule 11.3 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_11_03.c>`_
- Required
- A cast shall not be performed between a pointer to object type
and a pointer to a different object type
-
* - `Rule 11.6 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_11_06.c>`_
- Required
- A cast shall not be performed between pointer to void and an
arithmetic type
- All conversions to integer types are permitted if the destination
type has enough bits to hold the entire value. Conversions to
bool are permitted.
* - `Rule 11.7 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_11_07.c>`_
- Required
- A cast shall not be performed between pointer to object and a noninteger arithmetic type
-
* - `Rule 11.8 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_11_08.c>`_
- Required
- A cast shall not remove any const or volatile qualification from the type pointed to by a pointer
-
* - `Rule 11.9 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_11_09.c>`_
- Required
- The macro NULL shall be the only permitted form of null pointer constant
-
* - `Rule 12.5 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_12_05.c>`_
- Mandatory
- The sizeof operator shall not have an operand which is a function
parameter declared as "array of type"
-
* - `Rule 13.1 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_13_01_1.c>`_
- Required
- Initializer lists shall not contain persistent side effects
-
* - `Rule 13.6 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_13_06.c>`_
- Required
- The operand of the sizeof operator shall not contain any
expression which has potential side effects
- In addition to sizeof, we also want to apply the rule to typeof
and alignof
* - `Rule 14.1 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_14_01.c>`_
- Required
- A loop counter shall not have essentially floating type
-
* - `Rule 14.3 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_14_03.c>`_
- Required
- Controlling expressions shall not be invariant
- Due to the extensive usage of IS_ENABLED, sizeof compile-time
checks, and other constructs that are detected as errors by MISRA
C scanners, managing the configuration of a MISRA C scanner for
this rule would be unmanageable. Thus, this rule is adopted with
a project-wide deviation on if, ?:, switch(sizeof(...)), and
switch(offsetof(...)) statements.
while(0) and while(1) and alike are allowed.
* - `Rule 14.4 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_14_04.c>`_
- Required
- The controlling expression of an if-statement and the controlling
expression of an iteration-statement shall have essentially
Boolean type
- Automatic conversions of integer types to bool are permitted.
Automatic conversions of pointer types to bool are permitted.
This rule still applies to enum types.
* - `Rule 16.3 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_16_03.c>`_
- Required
- An unconditional break statement shall terminate every switch-clause_
- In addition to break, also other unconditional flow control statements
such as continue, return, goto are allowed.
* - `Rule 16.4 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_16_04.c>`_
- Required
- Every switch statement shall have a default label
- Switch statements with enums as controlling expression don't need
a default label as gcc -Wall enables -Wswitch which warns (and
breaks the build as we use -Werror) if one of the enum labels is
missing from the switch.
Switch statements with integer types as controlling expression
should have a default label:
- if the switch is expected to handle all possible cases
explicitly, then a default label shall be added to handle
unexpected error conditions, using BUG(), ASSERT(), WARN(),
domain_crash(), or other appropriate methods;
- if the switch is expected to handle a subset of all possible
cases, then an empty default label shall be added with an
in-code comment on top of the default label with a reason and
when possible a more detailed explanation. Example::
default:
/* Notifier pattern */
break;
* - `Rule 16.2 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_16_02.c>`_
- Required
- A switch label shall only be used when the most closely-enclosing
compound statement is the body of a switch statement
- The x86 emulator (xen/arch/x86/x86_emulate*) is exempt from
compliance with this rule. Efforts to make the x86 emulator
adhere to Rule 16.2 would result in increased complexity and
maintenance difficulty, and could potentially introduce bugs.
* - `Rule 16.6 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_16_06.c>`_
- Required
- Every switch statement shall have at least two switch-clauses
- Single-clause switches are allowed when they do not involve a
default label.
* - `Rule 16.7 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_16_07.c>`_
- Required
- A switch-expression shall not have essentially Boolean type
-
* - `Rule 17.1 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_17_01.c>`_
- Required
- The features of <stdarg.h> shall not be used
-
* - `Rule 17.3 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_17_03.c>`_
- Mandatory
- A function shall not be declared implicitly
-
* - `Rule 17.4 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_17_04.c>`_
- Mandatory
- All exit paths from a function with non-void return type shall
have an explicit return statement with an expression
-
* - `Rule 17.5 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_17_05.c>`_
- Advisory
- The function argument corresponding to a parameter declared to
have an array type shall have an appropriate number of elements
-
* - `Rule 17.6 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_17_06.c>`_
- Mandatory
- The declaration of an array parameter shall not contain the
static keyword between the [ ]
-
* - `Rule 17.7 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_17_07.c>`_
- Required
- The value returned by a function having non-void return type
shall be used
- Please beware that this rule has many violations in the Xen
codebase today, and its adoption is aspirational. However, when
submitting new patches please try to decrease the number of
violations when possible.
* - `Rule 18.3 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_18_03.c>`_
- 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 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_19_01.c>`_
- 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 20.4 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_20_04.c>`_
- Required
- A macro shall not be defined with the same name as a keyword
-
* - `Rule 20.7 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_20_07.c>`_
- Required
- Expressions resulting from the expansion of macro parameters
shall be enclosed in parentheses
- Extra parentheses are not required when macro parameters are used
as function arguments, as macro arguments, array indices, lhs in
assignments or as initializers in initalizer lists.
* - `Rule 20.9 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_20_09.c>`_
- Required
- All identifiers used in the controlling expression of #if or
#elif preprocessing directives shall be #define'd before
evaluation
-
* - `Rule 20.12 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_20_12.c>`_
- 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
- Variadic macros are allowed to violate the rule.
* - `Rule 20.13 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_20_13.c>`_
- Required
- A line whose first token is # shall be a valid preprocessing
directive
-
* - `Rule 20.14 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_20_14.c>`_
- 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 21.1 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_21_01.c>`_
- Required
- #define and #undef shall not be used on a reserved identifier or
reserved macro name
- Identifiers starting with an underscore followed by another underscore
or an upper-case letter are reserved. Today Xen uses many, such as
header guards and bitwise manipulation functions. Upon analysis it turns
out Xen identifiers do not clash with the identifiers used by modern
GCC, but that is not a guarantee that there won't be a naming clash in
the future or with another compiler. For these reasons we discourage
the introduction of new reserved identifiers in Xen, and we see it as
positive the reduction of reserved identifiers. At the same time,
certain identifiers starting with two underscores are also commonly used
in Linux (e.g. __set_bit) and we don't think it would be an improvement
to rename them.
* - `Rule 21.2 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_21_02.c>`_
- Required
- A reserved identifier or reserved macro name shall not be
declared
- See comment for Rule 21.1
* - `Rule 21.6 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_21_06.c>`_
- Required
- The Standard Library input/output routines shall not be used
- Xen doesn't provide, use, or link against a Standard Library [#xen-stdlib]_
* - `Rule 21.9 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_21_09.c>`_
- Required
- The library functions bsearch and qsort of <stdlib.h> shall not be used
- Xen doesn't provide, use, or link against a Standard Library [#xen-stdlib]_
* - `Rule 21.10 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_21_10.c>`_
- Required
- The Standard Library time and date routines shall not be used
- Xen doesn't provide, use, or link against a Standard Library [#xen-stdlib]_
* - `Rule 21.13 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_21_13.c>`_
- Mandatory
- Any value passed to a function in <ctype.h> shall be representable as an
unsigned char or be the value EOF
-
* - `Rule 21.14 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_21_14.c>`_
- Required
- The Standard Library function memcmp shall not be used to compare
null terminated strings
-
* - `Rule 21.15 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_21_15.c>`_
- Required
- The pointer arguments to the Standard Library functions memcpy,
memmove and memcmp shall be pointers to qualified or unqualified
versions of compatible types
-
* - `Rule 21.16 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_21_16.c>`_
- Required
- The pointer arguments to the Standard Library function memcmp
shall point to either a pointer type, an essentially signed type,
an essentially unsigned type, an essentially Boolean type or an
essentially enum type
- void* arguments are allowed
* - `Rule 21.17 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_21_17.c>`_
- 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 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_21_18.c>`_
- Mandatory
- The size_t argument passed to any function in <string.h> shall have an
appropriate value
-
* - `Rule 21.19 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_21_19.c>`_
- 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 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_21_20.c>`_
- 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 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/>`_
- Required
- The Standard Library function system of <stdlib.h> shall not be used
-
* - `Rule 22.2 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_22_02.c>`_
- Mandatory
- A block of memory shall only be freed if it was allocated by means of a
Standard Library function
-
* - `Rule 22.4 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_22_04.c>`_
- Mandatory
- There shall be no attempt to write to a stream which has been opened as
read-only
-
* - `Rule 22.5 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_22_05.c>`_
- Mandatory
- A pointer to a FILE object shall not be dereferenced
-
* - `Rule 22.6 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_22_06.c>`_
- Mandatory
- The value of a pointer to a FILE shall not be used after the associated
stream has been closed
-
Terms & Definitions
-------------------
.. _switch-clause:
A *switch clause* can be defined as:
"the non-empty list of statements which follows a non-empty list of
case/default labels".
A formal definition is available within the amplification of MISRA C:2012
Rule 16.1.
.. rubric:: Footnotes
.. [#xen-stdlib] Xen implements itself a few functions with names that match
the corresponding function names of the Standard Library for developers'
convenience. These functions are part of the Xen code and subject to
analysis.