| R2.1 |
The compiler implementation guarantees that the unreachable code is
removed. Constant expressions and unreachable branches of if and switch
statements are expected. |
Tagged as safe for ECLAIR. |
| R2.1 |
Unreachability caused by calls to the following functions or macros
is deliberate and there is no risk of code being unexpectedly left
out. |
- Tagged as deliberate for ECLAIR. Such
macros are:
-
- BUG
- assert_failed
- __builtin_unreachable
- ASSERT_UNREACHABLE
|
| R2.1 |
Pure declarations, that is, declarations without initializations are
not executable, and therefore it is safe for them to be unreachable. The
most notable example of such a pattern being used in the codebase is
that of a variable declaration that should be available in all the
clauses of a switch statement. |
ECLAIR has been configured to ignore those statements. |
| R2.1 |
The asm-offset files are not linked deliberately, since they are
used to generate definitions for asm modules. |
Tagged as deliberate for ECLAIR. |
| R2.2 |
Proving compliance with respect to Rule 2.2 is generally impossible:
see https://arxiv.org/abs/2212.13933
for details. Moreover, peer review gives us confidence that no evidence
of errors in the program's logic has been missed due to undetected
violations of Rule 2.2, if any. Testing on time behavior gives us
confidence on the fact that, should the program contain dead code that
is not removed by the compiler, the resulting slowdown is
negligible. |
Project-wide deviation, tagged as disapplied for ECLAIR. |
| R2.6 |
Labels deliberately marked as unused trough the pseudo-attribute
__maybe_unused are either the result of
them not being in certain build configurations, or as a deliberate
practice (e.g., unimplemented_insn).
Given that the compiler is then entitled to remove them, the presence of
such labels poses no risks. |
Tagged as deliberate for ECLAIR. |
| R3.1 |
Comments starting with '/*' and containing hyperlinks are safe as
they are not instances of commented-out code. |
Tagged as safe for ECLAIR. |
| R5.3 |
As specified in rules.rst, shadowing due to macros being used as
macro arguments is allowed, as it's deemed not at risk of causing
developer confusion. |
- Tagged as safe for ECLAIR. So far,
the following macros are deviated:
-
- READ_SYSREG and WRITE_SYSREG
- max{t}? and min{t}?
- read[bwlq] and read[bwlq]relaxed
- per_cpu and this_cpu
- __emulate_2op and __emulate_2op_nobyte
- read_debugreg and write_debugreg
|
| R5.5 |
Macros expanding to their own name are allowed. |
Tagged as deliberate for ECLAIR. |
| R5.5 |
Clashes between names of function-like macros and identifiers of
non-callable entities are allowed. |
Tagged as deliberate for ECLAIR. |
| R5.5 |
Clashes between function names and macros are deliberate for string
handling functions since some architectures may want to use their own
arch-specific implementation. |
Tagged as deliberate for ECLAIR. |
| R5.5 |
In libelf, clashes between macros and function names are deliberate
and needed to prevent the use of undecorated versions of memcpy, memset
and memmove. |
Tagged as deliberate for ECLAIR. |
| R5.6 |
The type ret_t is deliberately defined multiple times depending on
the type of guest to service. |
Tagged as deliberate for ECLAIR. |
| R5.6 |
On X86, some types are deliberately defined multiple times,
depending on the number of guest paging levels. |
- Tagged as deliberate for ECLAIR. Such
types are:
-
- guest_intpte_t
- guest_l[12]e_t
|
| R5.6 |
Some files are not subject to respect MISRA rules at the moment,
but, among these out-of-scope files, there are definitions of typedef
names that are already defined within in-scope files and therefore,
ECLAIR does report a violation since not all the files involved in the
violation are excluded from the analysis. |
- Tagged as deliberate for ECLAIR. Such
excluded files are:
-
- xen/include/efi/*
- xen/arch//include/asm//efibind.h
|
| R7.1 |
It is safe to use certain octal constants the way they are defined
in specifications, manuals, and algorithm descriptions. Such places are
marked safe with a /* octal-ok */ in-code comment. |
Tagged as safe for ECLAIR. |
| R7.2 |
Violations caused by __HYPERVISOR_VIRT_START are related to the
particular use of it done in xen_mk_ulong. |
Tagged as deliberate for ECLAIR. |
| R7.4 |
Allow pointers of non-character type as long as the pointee is
const-qualified. |
ECLAIR has been configured to ignore these assignments. |
| R8.3 |
The type ret_t is deliberately used and defined as int or long
depending on the architecture. |
Tagged as deliberate for ECLAIR. |
| R8.3 |
Some files are not subject to respect MISRA rules at the moment, but
some entity from a file in scope is used; therefore ECLAIR does report a
violation, since not all the files involved in the violation are
excluded from the analysis. |
- Tagged as deliberate for ECLAIR. Such
excluded files are:
-
- xen/arch/x86/time.c
- xen/arch/x86/acpi/cpu_idle.c
- xen/arch/x86/mpparse.c
- xen/common/bunzip2.c
- xen/common/unlz4.c
- xen/common/unlzma.c
- xen/common/unlzo.c
- xen/common/unxz.c
- xen/common/unzstd.c
|
| R8.3 |
Parameter name "unused" (with an optional numeric suffix) is
deliberate and makes explicit the intention of not using such parameter
within the function. |
Tagged as deliberate for ECLAIR. |
| R8.4 |
The definitions present in the files 'asm-offsets.c' for any
architecture are used to generate definitions for asm modules, and are
not called by C code. Therefore the absence of prior declarations is
safe. |
Tagged as safe for ECLAIR. |
| R8.4 |
The functions defined in the file xen/common/coverage/gcov_base.c
are meant to be called from gcc-generated code in a non-release build
configuration. Therefore, the absence of prior declarations is
safe. |
Tagged as safe for ECLAIR. |
| R8.4 |
Functions and variables used only by asm modules are marked with the
asmlinkage macro. Existing code may use a
SAF-1-safe textual deviation (see safe.json), but new code should not
use it. |
Tagged as safe for ECLAIR. |
| R8.4 |
Some functions are excluded from non-debug build, therefore the
absence of declaration is safe. |
- Tagged as safe for ECLAIR, such
functions are:
-
- apei_read_mce()
- apei_check_mce()
- apei_clear_mce()
|
| R8.4 |
Given that bsearch and sort are defined with the attribute
'gnu_inline', it's deliberate not to have a prior declaration. See
Section "6.33.1 Common Function Attributes" of "GCC_MANUAL" for a full
explanation of gnu_inline. |
Tagged as deliberate for ECLAIR. |
| R8.4 |
first_valid_mfn is defined in this way because the current lack of
NUMA support in Arm and PPC requires it. |
Tagged as deliberate for ECLAIR. |
| R8.6 |
The following variables are compiled in multiple translation units
belonging to different executables and therefore are safe.
- current_stack_pointer
- bsearch
- sort
|
Tagged as safe for ECLAIR. |
| R8.6 |
Declarations without definitions are allowed (specifically when the
definition is compiled-out or optimized-out by the compiler). |
Tagged as deliberate in ECLAIR. |
| R8.6 |
The search procedure for Unix linkers is well defined, see ld(1)
manual: "The linker will search an archive only once, at the location
where it is specified on the command line. If the archive defines a
symbol which was undefined in some object which appeared before the
archive on the command line, the linker will include the appropriate
file(s) from the archive". In Xen, thanks to the order in which file
names appear in the build commands, if arch-specific definitions are
present, they get always linked in before searching in the lib.a archive
resulting from xen/lib. |
Tagged as deliberate for ECLAIR. |
| R8.10 |
The gnu_inline attribute without static is deliberately
allowed. |
Tagged as deliberate for ECLAIR. |
| R9.5 |
The possibility of committing mistakes by specifying an explicit
dimension is higher than omitting the dimension, therefore all such
instances of violations are deviated. |
Project-wide deviation, tagged as deliberate for ECLAIR. |
| R10.1, R10.3, R10.4 |
The value-preserving conversions of integer constants are safe. |
Tagged as safe for ECLAIR. |
| R10.1 |
Shifting non-negative integers to the right is safe. |
Tagged as safe for ECLAIR. |
| R10.1 |
Shifting non-negative integers to the left is safe if the result is
still non-negative. |
Tagged as safe for ECLAIR. |
| R10.1 |
Bitwise logical operations on non-negative integers are safe. |
Tagged as safe for ECLAIR. |
| R10.1 |
The implicit conversion to Boolean for logical operator arguments is
well-known to all Xen developers to be a comparison with 0. |
Tagged as safe for ECLAIR. |
| R10.1 |
Xen only supports architectures where signed integers are
representend using two's complement and all the Xen developers are aware
of this. For this reason, bitwise operations are safe. |
Tagged as safe for ECLAIR. |
| R10.1 |
Given the assumptions on the toolchain detailed in
docs/misra/C-language-toolchain.rst and the build flags used by the
project, it is deemed safe to use bitwise shift operators. See
automation/eclair_analysis/deviations.ecl for the full explanation. |
Tagged as safe for ECLAIR. |
| R10.1 |
The macro ISOLATE_LSB encapsulates the well-known pattern (x &
-x) applied to unsigned integer values on 2's complement architectures
(i.e., all architectures supported by Xen), used to obtain a mask where
just the least significant nonzero bit of x is set. If no bits are set,
0 is returned. |
Tagged as safe for ECLAIR. |
| R11.1 |
The conversion from a function pointer to unsigned long or (void *)
does not lose any information, provided that the target type has enough
bits to store it. |
Tagged as safe for ECLAIR. |
| R11.1 |
The conversion from a function pointer to a boolean has a well-known
semantics that do not lead to unexpected behaviour. |
Tagged as safe for ECLAIR. |
| R11.2 |
The conversion from a pointer to an incomplete type to unsigned long
does not lose any information, provided that the target type has enough
bits to store it. |
Tagged as safe for ECLAIR. |
| R11.3 |
Conversions to object pointers that have a pointee type with a
smaller (i.e., less strict) alignment requirement are safe. |
Tagged as safe for ECLAIR. |
| R11.6 |
Conversions from and to integral types are safe, in the assumption
that the target type has enough bits to store the value. See also
Section "4.7 Arrays and Pointers" of "GCC_MANUAL" |
Tagged as safe for ECLAIR. |
| R11.6 |
The conversion from a pointer to a boolean has a well-known
semantics that do not lead to unexpected behaviour. |
Tagged as safe for ECLAIR. |
| R11.8 |
Violations caused by container_of are due to pointer arithmetic
operations with the provided offset. The resulting pointer is then
immediately cast back to its original type, which preserves the
qualifier. This use is deemed safe. Fixing this violation would require
to increase code complexity and lower readability. |
Tagged as safe for ECLAIR. |
| R11.9 |
__ACCESS_ONCE uses an integer, which happens to be zero, as a
compile time check. The typecheck uses a cast. The usage of zero or
other integers for this purpose is allowed. |
Tagged as deliberate for ECLAIR. |
| R13.5 |
All developers and reviewers can be safely assumed to be well aware
of the short-circuit evaluation strategy for logical operators. |
Project-wide deviation; tagged as disapplied for ECLAIR. |
| R13.6 |
On x86, macros alternative_v?call[0-9] use sizeof and typeof to
check that the argument types match the corresponding parameter
ones. |
Tagged as deliberate for ECLAIR. |
| R13.6 |
Anything, no matter how complicated, inside the BUILD_BUG_ON macro
is subject to a compile-time evaluation without relevant side
effects." |
Tagged as safe for ECLAIR. |
| R14.2 |
The severe restrictions imposed by this rule on the use of 'for'
statements are not counterbalanced by the presumed facilitation of the
peer review activity. |
Project-wide deviation; tagged as disapplied for ECLAIR. |
| R14.3 |
The Xen team relies on the fact that invariant conditions of 'if'
statements and conditional operators are deliberate. |
Tagged as deliberate for ECLAIR. |
| R14.3 |
Switches having a 'sizeof' operator as the condition are deliberate
and have limited scope. |
Tagged as deliberate for ECLAIR. |
| R14.3 |
The use of an invariant size argument in {put,get}_unsafe_size and
array_access_ok, as defined in arch/x86(_64)?/include/asm/uaccess.h is
deliberate and is deemed safe. |
Tagged as deliberate for ECLAIR. |
| R14.4 |
A controlling expression of 'if' and iteration statements having
integer, character or pointer type has a semantics that is well-known to
all Xen developers. |
Tagged as deliberate for ECLAIR. |
| R14.4 |
The XEN team relies on the fact that the enum is_dying has the
constant with assigned value 0 act as false and the other ones as true,
therefore have the same behavior of a boolean. |
Tagged as deliberate for ECLAIR. |
| R16.2 |
Complying with the Rule would entail a lot of code duplication in
the implementation of the x86 emulator, therefore it is deemed better to
leave such files as is. |
Tagged as deliberate for ECLAIR. |
| R16.3 |
Statements that change the control flow (i.e., break, continue,
goto, return) and calls to functions that do not return the control back
are "allowed terminal statements". |
Tagged as safe for ECLAIR. |
| R16.3 |
An if-else statement having both branches ending with one of the
allowed terminal statemets is itself an allowed terminal
statements. |
Tagged as safe for ECLAIR. |
| R16.3 |
An if-else statement having an always true condition and the true
branch ending with an allowed terminal statement is itself an allowed
terminal statement. |
Tagged as safe for ECLAIR. |
| R16.3 |
A switch clause ending with a statement expression which, in turn,
ends with an allowed terminal statement (e.g., the expansion of
generate_exception()) is safe. |
Tagged as safe for ECLAIR. |
| R16.3 |
A switch clause ending with a do-while-false the body of which, in
turn, ends with an allowed terminal statement (e.g., PARSE_ERR_RET()) is
safe. An exception to that is the macro ASSERT_UNREACHABLE() which is
effective in debug build only: a switch clause ending with
ASSERT_UNREACHABLE() is not considered safe. |
Tagged as safe for ECLAIR. |
| R16.3 |
Switch clauses ending with pseudo-keyword "fallthrough" are
safe. |
Tagged as safe for ECLAIR. |
| R16.3 |
Switch clauses ending with failure method "BUG()" are safe. |
Tagged as safe for ECLAIR. |
| R16.3 |
Existing switch clauses not ending with the break statement are safe
if an explicit comment indicating the fallthrough intention is present.
However, the use of such comments in new code is deprecated: the
pseudo-keyword "fallthrough" shall be used. |
- Tagged as safe for ECLAIR. The
accepted comments are:
-
- /* fall through */
- /* fall through. */
- /* fallthrough */
- /* fallthrough. */
- /* Fall through */
- /* Fall through. */
- /* Fallthrough */
- /* Fallthrough. */
|
| R16.4 |
Switch statements having a controlling expression of enum type
deliberately do not have a default case: 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. |
Tagged as deliberate for ECLAIR. |
| R16.4 |
A switch statement with a single switch clause and no default label
may be used in place of an equivalent if statement if it is considered
to improve readability. |
Tagged as deliberate for ECLAIR. |
| R16.6 |
A switch statement with a single switch clause and no default label
may be used in place of an equivalent if statement if it is considered
to improve readability. |
Tagged as deliberate for ECLAIR. |
| R17.1 |
printf()-like functions are allowed to use the variadic features
provided by stdarg.h. |
Tagged as deliberate for ECLAIR. |
| R17.7 |
Not using the return value of a function does not endanger safety if
it coincides with an actual argument. |
- Tagged as safe for ECLAIR. Such
functions are:
-
- __builtin_memcpy()
- __builtin_memmove()
- __builtin_memset()
- cpumask_check()
|
| R18.2 |
Subtractions between pointers where at least one of the operand is a
pointer to a symbol defined by the linker are safe. |
Tagged as safe for ECLAIR. |
| R18.2 |
Subtraction between pointers encapsulated by macro page_to_mfn are
safe. |
Tagged as safe for ECLAIR. |
| R20.4 |
The override of the keyword "inline" in xen/compiler.h is present so
that section contents checks pass when the compiler chooses not to
inline a particular function. |
Comment-based deviation. |
| R20.7 |
Code violating Rule 20.7 is safe when macro parameters are used:
- as function arguments;
- as macro arguments;
- as array indices;
- as lhs in assignments;
- as initializers, possibly designated, in initalizer lists;
- as constant expressions of switch case labels.
|
Tagged as safe for ECLAIR. |
| R20.7 |
Violations due to the use of macros defined in files that are not in
scope for compliance are allowed, as that is imported code. |
Tagged as safe for ECLAIR. |
| R20.7 |
To avoid compromising readability, the macros alternative_(v)?call[0-9] are allowed not to
parenthesize their arguments, as there are already sanity checks in
place. |
Tagged as safe for ECLAIR. |
| R20.7 |
The macro count_args_ is not
compliant with the rule, but is not likely to incur in the risk of being
misused or lead to developer confusion, and refactoring it to add
parentheses breaks its functionality. |
Tagged as safe for ECLAIR. |
| R20.7 |
The macros {COMPILE,RUNTIME}_CHECK
defined in xen/include/xen/self-tests.h
are allowed not to parenthesize the "fn" argument, to allow
function-like macros to be tested as well as functions. Given the
specialized use of these macros and their limited usage scope, omitting
parentheses is deemed unlikely to cause issues. |
Tagged as deliberate for ECLAIR. |
| R20.7 |
Problems related to operator precedence can not occur if the
expansion of the macro argument is surrounded by tokens '{', '}' and
';'. |
Tagged as safe for ECLAIR. |
| R20.12 |
Variadic macros that use token pasting often employ the gcc
extension ext_paste_comma, as detailed in
C-language-toolchain.rst, which is not
easily replaceable; macros that in addition perform regular argument
expansion on the same argument subject to the # or ## operators violate
the Rule if the argument is a macro. |
Tagged as deliberate for ECLAIR. |
| R20.12 |
Macros that are used for runtime or build-time assertions contain
deliberate uses of an argument as both a regular argument and a
stringification token, to provide useful diagnostic messages. |
Tagged as deliberate for ECLAIR. |
| R20.12 |
GENERATE_CASE is a local helper macro that allows some selected
switch statements to be more compact and readable. As such, the risk of
developer confusion in using such macro is deemed negligible. This
construct is deviated only in Translation Units that present a violation
of the Rule due to uses of this macro. |
Tagged as deliberate for ECLAIR. |
| R21.9 |
Xen does not use the bsearch and
qsort functions provided by the C
Standard Library, but provides in source form its own implementation,
therefore any unspecified or undefined behavior associated to the
functions provided by the Standard Library does not apply. Any such
behavior that may exist in such functions is therefore under the
jurisdiction of other MISRA C rules. |
Project-wide deviation, tagged as deliberate for ECLAIR. |
| R21.10 |
Xen does not use the facilities provided by the <time.h> provided by the C Standard
Library, but provides in source form its own implementation, therefore
any unspecified, undefined or implementation-defined behavior associated
to the functions provided by the Standard Library does not apply. Any
such behavior that may exist in such functions is therefore under the
jurisdiction of other MISRA C rules. |
Project-wide deviation, tagged as deliberate for ECLAIR. |