Re: [PATCH v1] misra: add deviation for rules 21.1 and 21.2

[Dmytro Prokopchuk1 <dmytro_prokopchuk1@xxxxxxxx>]

On 7/18/25 08:31, Jan Beulich wrote:
> On 17.07.2025 22:47, Dmytro Prokopchuk1 wrote:
>>
>>
>> On 4/23/25 20:54, victorm.lira@xxxxxxx wrote:
>>> From: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
>>>
>>> MISRA C Rules 21.1 ("#define and #undef shall not be used on a
>>> reserved identifier or reserved macro name") and R21.2 ("A reserved
>>> identifier or reserved macro name shall not be declared") violations
>>> are not problematic for Xen, as it does not use the C or POSIX
>>> libraries.
>>>
>>> Xen uses -fno-builtin and -nostdinc to ensure this, but there are still
>>> __builtin_* functions from the compiler that are available so
>>> a deviation is formulated for all identifiers not starting with
>>> "__builtin_".
>>>
>>> The missing text of a deviation for Rule 21.2 is added to
>>> docs/misra/deviations.rst.
>>>
>>> To avoid regressions, tag both rules as clean and add them to the
>>> monitored set.
>>>
>>> Signed-off-by: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
>>> Signed-off-by: Federico Serafini <federico.serafini@xxxxxxxxxxx>
>>> Signed-off-by: Victor Lira <victorm.lira@xxxxxxx>
>>> Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
>>> ---
>>> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>> Cc: Anthony PERARD <anthony.perard@xxxxxxxxxx>
>>> Cc: Michal Orzel <michal.orzel@xxxxxxx>
>>> Cc: Jan Beulich <jbeulich@xxxxxxxx>
>>> Cc: Julien Grall <julien@xxxxxxx>
>>> Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>>> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
>>> Cc: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
>>> Cc: Federico Serafini <federico.serafini@xxxxxxxxxxx>
>>> Cc: Bertrand Marquis <bertrand.marquis@xxxxxxx>
>>> ---
>>>    .../eclair_analysis/ECLAIR/deviations.ecl     |  9 ++++++-
>>>    .../eclair_analysis/ECLAIR/monitored.ecl      |  2 ++
>>>    automation/eclair_analysis/ECLAIR/tagging.ecl |  2 ++
>>>    docs/misra/deviations.rst                     | 26 ++++++++++++++++++-
>>>    4 files changed, 37 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/automation/eclair_analysis/ECLAIR/deviations.ecl 
>>> b/automation/eclair_analysis/ECLAIR/deviations.ecl
>>> index 2c8fb92713..ffa23b53b7 100644
>>> --- a/automation/eclair_analysis/ECLAIR/deviations.ecl
>>> +++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
>>> @@ -639,8 +639,15 @@ in the expansion."
>>>    # Series 21.
>>>    #
>>>
>>> +-doc_begin="Xen does not use C and POSIX libraries:
>>> +identifiers reserved by these libraries can be used safely, except for 
>>> those
>>> +beginning with '__builtin_'."
>>> +-config=MC3A2.R21.1,macros={safe, "!^__builtin_.*$"}
>>> +-config=MC3A2.R21.2,declarations={safe, "!^__builtin_.*$"}
>>> +-doc_end
>>> +
>>>    -doc_begin="or, and and xor are reserved identifiers because they 
>>> constitute alternate
>>> -spellings for the corresponding operators (they are defined as macros by 
>>> iso646.h).
>>> +spellings for the corresponding logical operators (as defined in header 
>>> 'iso646.h').
>>>    However, Xen doesn't use standard library headers, so there is no risk 
>>> of overlap."
>>>    -config=MC3A2.R21.2,reports+={safe, 
>>> "any_area(stmt(ref(kind(label)&&^(or|and|xor|not)$)))"}
>>>    -doc_end
>>> diff --git a/automation/eclair_analysis/ECLAIR/monitored.ecl 
>>> b/automation/eclair_analysis/ECLAIR/monitored.ecl
>>> index 8351996ec8..da229a0d84 100644
>>> --- a/automation/eclair_analysis/ECLAIR/monitored.ecl
>>> +++ b/automation/eclair_analysis/ECLAIR/monitored.ecl
>>> @@ -79,6 +79,8 @@
>>>    -enable=MC3A2.R20.12
>>>    -enable=MC3A2.R20.13
>>>    -enable=MC3A2.R20.14
>>> +-enable=MC3A2.R21.1
>>> +-enable=MC3A2.R21.2
>>>    -enable=MC3A2.R21.3
>>>    -enable=MC3A2.R21.4
>>>    -enable=MC3A2.R21.5
>>> diff --git a/automation/eclair_analysis/ECLAIR/tagging.ecl 
>>> b/automation/eclair_analysis/ECLAIR/tagging.ecl
>>> index 1d078d8905..3292bf751e 100644
>>> --- a/automation/eclair_analysis/ECLAIR/tagging.ecl
>>> +++ b/automation/eclair_analysis/ECLAIR/tagging.ecl
>>> @@ -88,6 +88,8 @@ MC3A2.R20.11||
>>>    MC3A2.R20.12||
>>>    MC3A2.R20.13||
>>>    MC3A2.R20.14||
>>> +MC3A2.R21.1||
>>> +MC3A2.R21.2||
>>>    MC3A2.R21.3||
>>>    MC3A2.R21.4||
>>>    MC3A2.R21.5||
>>> diff --git a/docs/misra/deviations.rst b/docs/misra/deviations.rst
>>> index fe0b1e10a2..88328eaa8a 100644
>>> --- a/docs/misra/deviations.rst
>>> +++ b/docs/misra/deviations.rst
>>> @@ -587,7 +587,31 @@ Deviations related to MISRA C:2012 Rules:
>>>           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.
>>> -
>>> +
>>> +   * - R21.1
>>> +     - Rule 21.1 reports identifiers reserved for the C and POSIX standard
>>> +       libraries. Xen does not use such libraries and all translation units
>>> +       are compiled with option '-nostdinc', therefore there is no reason 
>>> to
>>> +       avoid to use `#define` or `#undef` on such identifiers except for 
>>> those
>>> +       beginning with `__builtin_` for which compilers may perform (wrong)
>>> +       optimizations.
>>> +     - Tagged as `safe` for ECLAIR.
>>> +
>>> +   * - R21.2
>>> +     - Rule 21.2 reports identifiers reserved for the C and POSIX standard
>>> +       libraries. Xen does not use such libraries and all translation units
>>> +       are compiled with option '-nostdinc', therefore there is no reason 
>>> to
>>> +       avoid declaring such identifiers except for those beginning with
>>> +       `__builtin_` for which compilers may perform (wrong) optimizations.
>>> +     - Tagged as `safe` for ECLAIR.
>>> +
>>> +   * - R21.2
>>> +     - `or`, `and` and `xor` are reserved identifiers because they 
>>> constitute
>>> +       alternate spellings for the corresponding logical operators
>>> +       (as defined in Standard Library header `\<iso646.h\>`). Xen does 
>>> not use
>>> +       Standard library headers, so there is no risk of overlap.
>>> +     - Tagged as `safe` 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,
>>> --
>>> 2.47.0
>>
>> Hello All!
>>
>> I tried to play with Rule 21.1 deviations.
>>
>> After applying the following configurations:
>>
>> -config=MC3A2.R21.1,macros+={safe, "^offsetof$ || ^(is|to)[a-z]+$ ||
>> name(NULL) || name(bool) || name(true) || name(false)"}
>> -config=MC3A2.R21.1,macros+={safe,
>> "loc(file(^xen/include/xen/inttypes\\.h$))"}
>> -config=MC3A2.R21.1,macros+={safe, "loc(file(^xen/include/xen/types\\.h$))"}
>> -config=MC3A2.R21.1,macros+={safe, "^str[a-z]+$ || ^(v)?sprintf$ ||
>> ^va_[a-z]+$"}
> 
> Can you spell these out in words? I can only vaguely interpret these Eclair
> patterns, sorry.
Yes, sure.

That means to deviate the following macros:
- offsetof
- begin with either ‘is’ or ‘to’ followed by a lowercase letters 
(islower, isdigit, tolower, toupper, etc.)
- NULL
- bool
- true
- false
- all PRI/SCN macros for printing/scanning format specifiers from header 
file xen/include/xen/inttypes.h
- all macros from header file xen/include/xen/types.h (limits: 
UINT8_MAX, INT_MAX, LONG_MIN, etc.)
- begin with 'str' followed by a lowercase letters (string functions)
- sprintf/vsprintf
- begin with 'va_' followed by a lowercase letters (va_copy, va_start, 
va_end, va_arg)

> 
>> Eclair showed 699 remaining violations.
>> All of them were related to names beginning with an underscore (_).
>>
>> It's possible to resolve the rest of them with help of (all, except for
>> those beginning with '__builtin_' and '__x86_64__'):
>>
>> -config=MC3A2.R21.1,macros+={safe, "^_.*$ && !^__builtin_.*$ &&
>> !^__x86_64__$"}
>>
>> Probably, the exception list can be extended.
>>
>> Jan,
>> I know you don't want to disallow "_all_" such reserved identifiers.
>> But how to deal with that?
> 
> How do I not want this? I've been arguing for years that we should respect
> the reserved name spaces. (Did you perhaps mean "... you don't want to
> deviate ..."?) There are exceptions, yes, e.g. ...
> 
Yes, I meant about deviations. Sorry.

>> Try to cover all macros? Like this, for example (I assume that there are
>> no such reserved macros):
>> -config=MC3A2.R21.1,macros+={safe, "^.*XEN.*$ || ^.*HYPERVISOR.*$"}
> 
> ... anything we may have (wrongly) introduced into the public headers. We
> can't very well change naming there.
Looks like the only way is to deviate all macros (that are currently 
used in Xen), tag rule as "clean" and prohibit using reserved names in 
the future.

Any suggestions?

Dmytro

> 
> Jan