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[XEN PATCH] xen/bitmap: remove comment-based deviations

Federico Serafini posted 1 patch 2 months, 3 weeks ago
Patches applied successfully (tree, apply log)
git fetch https://gitlab.com/xen-project/patchew/xen tags/patchew/4aa692a50a5d08d24560f02fdc36911965fc860b.1724850701.git.federico.serafini@bugseng.com
automation/eclair_analysis/ECLAIR/deviations.ecl | 4 ++++
docs/misra/deviations.rst                        | 5 +++++
xen/include/xen/bitmap.h                         | 3 ---
3 files changed, 9 insertions(+), 3 deletions(-)
[XEN PATCH] xen/bitmap: remove comment-based deviations
Posted by Federico Serafini 2 months, 3 weeks ago 
Update ECLAIR configuration of MISRA C:2012 Rule 20.7 ("Expressions
resulting from the expansion of macro parameters shall be enclosed in
parentheses") to tag as 'safe' the expansions of arguments surrounded
by the following tokens: '{', '}' and ';'.

Remove redundant comment-based deviations.

Signed-off-by: Federico Serafini <federico.serafini@bugseng.com>
---
 automation/eclair_analysis/ECLAIR/deviations.ecl | 4 ++++
 docs/misra/deviations.rst                        | 5 +++++
 xen/include/xen/bitmap.h                         | 3 ---
 3 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/automation/eclair_analysis/ECLAIR/deviations.ecl b/automation/eclair_analysis/ECLAIR/deviations.ecl
index 1aa8277066..f37329973f 100644
--- a/automation/eclair_analysis/ECLAIR/deviations.ecl
+++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
@@ -565,6 +565,10 @@ of this macro do not lead to developer confusion, and can thus be deviated."
 -config=MC3R1.R20.7,reports+={safe, "any_area(any_loc(any_exp(macro(^count_args_$))))"}
 -doc_end
 
+-doc_begin="The expansion of an argument surrounded by tokens '{', '}' and ';' is safe."
+-config=MC3R1.R20.7,expansion_context+={safe, "left_right(^[\\{;]$,^[;\\}]$)"}
+-doc_end
+
 -doc_begin="Uses of variadic macros that have one of their arguments defined as
 a macro and used within the body for both ordinary parameter expansion and as an
 operand to the # or ## operators have a behavior that is well-understood and
diff --git a/docs/misra/deviations.rst b/docs/misra/deviations.rst
index d51aa422b5..d529726464 100644
--- a/docs/misra/deviations.rst
+++ b/docs/misra/deviations.rst
@@ -512,6 +512,11 @@ Deviations related to MISRA C:2012 Rules:
        refactoring it to add parentheses breaks its functionality.
      - Tagged as `safe` for ECLAIR.
 
+   * - R20.7
+     - The expansion of an argument surrounded by tokens '{', '}' and ';' is
+       safe.
+     - 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
diff --git a/xen/include/xen/bitmap.h b/xen/include/xen/bitmap.h
index 5d668053b0..4b642cd420 100644
--- a/xen/include/xen/bitmap.h
+++ b/xen/include/xen/bitmap.h
@@ -103,13 +103,10 @@ extern int bitmap_allocate_region(unsigned long *bitmap, int pos, int order);
 #define bitmap_switch(nbits, zero, small, large)			  \
 	unsigned int n__ = (nbits);					  \
 	if (__builtin_constant_p(nbits) && !n__) {			  \
-		/* SAF-7-safe Rule 20.7 non-parenthesized macro argument */ \
 		zero;							  \
 	} else if (__builtin_constant_p(nbits) && n__ <= BITS_PER_LONG) { \
-		/* SAF-7-safe Rule 20.7 non-parenthesized macro argument */ \
 		small;							  \
 	} else {							  \
-		/* SAF-7-safe Rule 20.7 non-parenthesized macro argument */ \
 		large;							  \
 	}
 
-- 
2.34.1
Re: [XEN PATCH] xen/bitmap: remove comment-based deviations
Posted by Stefano Stabellini 2 months, 3 weeks ago 
On Wed, 28 Aug 2024, Federico Serafini wrote:
> Update ECLAIR configuration of MISRA C:2012 Rule 20.7 ("Expressions
> resulting from the expansion of macro parameters shall be enclosed in
> parentheses") to tag as 'safe' the expansions of arguments surrounded
> by the following tokens: '{', '}' and ';'.
> 
> Remove redundant comment-based deviations.
> 
> Signed-off-by: Federico Serafini <federico.serafini@bugseng.com>

I am missing some context: is this done to cover other cases similar to
the one below (bitmap_allocate_region) or is this done only to get rid
of the three SAF-7-safe in-code comments?


> ---
>  automation/eclair_analysis/ECLAIR/deviations.ecl | 4 ++++
>  docs/misra/deviations.rst                        | 5 +++++
>  xen/include/xen/bitmap.h                         | 3 ---
>  3 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/automation/eclair_analysis/ECLAIR/deviations.ecl b/automation/eclair_analysis/ECLAIR/deviations.ecl
> index 1aa8277066..f37329973f 100644
> --- a/automation/eclair_analysis/ECLAIR/deviations.ecl
> +++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
> @@ -565,6 +565,10 @@ of this macro do not lead to developer confusion, and can thus be deviated."
>  -config=MC3R1.R20.7,reports+={safe, "any_area(any_loc(any_exp(macro(^count_args_$))))"}
>  -doc_end
>  
> +-doc_begin="The expansion of an argument surrounded by tokens '{', '}' and ';' is safe."
> +-config=MC3R1.R20.7,expansion_context+={safe, "left_right(^[\\{;]$,^[;\\}]$)"}
> +-doc_end
> +
>  -doc_begin="Uses of variadic macros that have one of their arguments defined as
>  a macro and used within the body for both ordinary parameter expansion and as an
>  operand to the # or ## operators have a behavior that is well-understood and
> diff --git a/docs/misra/deviations.rst b/docs/misra/deviations.rst
> index d51aa422b5..d529726464 100644
> --- a/docs/misra/deviations.rst
> +++ b/docs/misra/deviations.rst
> @@ -512,6 +512,11 @@ Deviations related to MISRA C:2012 Rules:
>         refactoring it to add parentheses breaks its functionality.
>       - Tagged as `safe` for ECLAIR.
>  
> +   * - R20.7
> +     - The expansion of an argument surrounded by tokens '{', '}' and ';' is
> +       safe.
> +     - 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
> diff --git a/xen/include/xen/bitmap.h b/xen/include/xen/bitmap.h
> index 5d668053b0..4b642cd420 100644
> --- a/xen/include/xen/bitmap.h
> +++ b/xen/include/xen/bitmap.h
> @@ -103,13 +103,10 @@ extern int bitmap_allocate_region(unsigned long *bitmap, int pos, int order);
>  #define bitmap_switch(nbits, zero, small, large)			  \
>  	unsigned int n__ = (nbits);					  \
>  	if (__builtin_constant_p(nbits) && !n__) {			  \
> -		/* SAF-7-safe Rule 20.7 non-parenthesized macro argument */ \
>  		zero;							  \
>  	} else if (__builtin_constant_p(nbits) && n__ <= BITS_PER_LONG) { \
> -		/* SAF-7-safe Rule 20.7 non-parenthesized macro argument */ \
>  		small;							  \
>  	} else {							  \
> -		/* SAF-7-safe Rule 20.7 non-parenthesized macro argument */ \
>  		large;							  \
>  	}
>  
> -- 
> 2.34.1
>
Re: [XEN PATCH] xen/bitmap: remove comment-based deviations
Posted by Federico Serafini 2 months, 3 weeks ago 
On 29/08/24 02:42, Stefano Stabellini wrote:
> On Wed, 28 Aug 2024, Federico Serafini wrote:
>> Update ECLAIR configuration of MISRA C:2012 Rule 20.7 ("Expressions
>> resulting from the expansion of macro parameters shall be enclosed in
>> parentheses") to tag as 'safe' the expansions of arguments surrounded
>> by the following tokens: '{', '}' and ';'.
>>
>> Remove redundant comment-based deviations.
>>
>> Signed-off-by: Federico Serafini <federico.serafini@bugseng.com>
> 
> I am missing some context: is this done to cover other cases similar to
> the one below (bitmap_allocate_region) or is this done only to get rid
> of the three SAF-7-safe in-code comments?

This is done to cover also other cases that may occur in the future.
More details here:
https://lists.xenproject.org/archives/html/xen-devel/2024-08/msg01392.html

-- 
Federico Serafini, M.Sc.

Software Engineer, BUGSENG (http://bugseng.com)
Re: [XEN PATCH] xen/bitmap: remove comment-based deviations
Posted by Jan Beulich 2 months, 3 weeks ago 
On 28.08.2024 15:12, Federico Serafini wrote:
> --- a/automation/eclair_analysis/ECLAIR/deviations.ecl
> +++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
> @@ -565,6 +565,10 @@ of this macro do not lead to developer confusion, and can thus be deviated."
>  -config=MC3R1.R20.7,reports+={safe, "any_area(any_loc(any_exp(macro(^count_args_$))))"}
>  -doc_end
>  
> +-doc_begin="The expansion of an argument surrounded by tokens '{', '}' and ';' is safe."
> +-config=MC3R1.R20.7,expansion_context+={safe, "left_right(^[\\{;]$,^[;\\}]$)"}
> +-doc_end

Not the least because this is quite a bit wider than ...

> --- a/xen/include/xen/bitmap.h
> +++ b/xen/include/xen/bitmap.h
> @@ -103,13 +103,10 @@ extern int bitmap_allocate_region(unsigned long *bitmap, int pos, int order);
>  #define bitmap_switch(nbits, zero, small, large)			  \
>  	unsigned int n__ = (nbits);					  \
>  	if (__builtin_constant_p(nbits) && !n__) {			  \
> -		/* SAF-7-safe Rule 20.7 non-parenthesized macro argument */ \
>  		zero;							  \
>  	} else if (__builtin_constant_p(nbits) && n__ <= BITS_PER_LONG) { \
> -		/* SAF-7-safe Rule 20.7 non-parenthesized macro argument */ \
>  		small;							  \
>  	} else {							  \
> -		/* SAF-7-safe Rule 20.7 non-parenthesized macro argument */ \
>  		large;							  \
>  	}

... what's needed here, I wonder if we're not opening up avenues to
problems by generally permitting that pattern. Plus in the description
I'm missing a statement to the effect of why this is (always) safe.

Jan
Re: [XEN PATCH] xen/bitmap: remove comment-based deviations
Posted by Federico Serafini 2 months, 3 weeks ago 
On 28/08/24 16:50, Jan Beulich wrote:
> On 28.08.2024 15:12, Federico Serafini wrote:
>> --- a/automation/eclair_analysis/ECLAIR/deviations.ecl
>> +++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
>> @@ -565,6 +565,10 @@ of this macro do not lead to developer confusion, and can thus be deviated."
>>   -config=MC3R1.R20.7,reports+={safe, "any_area(any_loc(any_exp(macro(^count_args_$))))"}
>>   -doc_end
>>   
>> +-doc_begin="The expansion of an argument surrounded by tokens '{', '}' and ';' is safe."
>> +-config=MC3R1.R20.7,expansion_context+={safe, "left_right(^[\\{;]$,^[;\\}]$)"}
>> +-doc_end
> 
> Not the least because this is quite a bit wider than ...
> 
>> --- a/xen/include/xen/bitmap.h
>> +++ b/xen/include/xen/bitmap.h
>> @@ -103,13 +103,10 @@ extern int bitmap_allocate_region(unsigned long *bitmap, int pos, int order);
>>   #define bitmap_switch(nbits, zero, small, large)			  \
>>   	unsigned int n__ = (nbits);					  \
>>   	if (__builtin_constant_p(nbits) && !n__) {			  \
>> -		/* SAF-7-safe Rule 20.7 non-parenthesized macro argument */ \
>>   		zero;							  \
>>   	} else if (__builtin_constant_p(nbits) && n__ <= BITS_PER_LONG) { \
>> -		/* SAF-7-safe Rule 20.7 non-parenthesized macro argument */ \
>>   		small;							  \
>>   	} else {							  \
>> -		/* SAF-7-safe Rule 20.7 non-parenthesized macro argument */ \
>>   		large;							  \
>>   	}
> 
> ... what's needed here, I wonder if we're not opening up avenues to
> problems by generally permitting that pattern. Plus in the description
> I'm missing a statement to the effect of why this is (always) safe.

The rational of the rule is that if a macro argument expands to an
expression, there may be problems related to operator precedence, e.g.:

#define A(x, y) x * y

A(1+1, 2+2) will expand to: 1+1 * 2+2

Yes, the deviation is more general and wider than what is needed for
the specific case but it is safe: if the expanded argument is between
one of the aforementioned tokens, then there are no operators involved
and no precedence issues.

I can add some details in a v2.

-- 
Federico Serafini, M.Sc.

Software Engineer, BUGSENG (http://bugseng.com)
Re: [XEN PATCH] xen/bitmap: remove comment-based deviations
Posted by Jan Beulich 2 months, 3 weeks ago 
On 30.08.2024 10:13, Federico Serafini wrote:
> On 28/08/24 16:50, Jan Beulich wrote:
>> On 28.08.2024 15:12, Federico Serafini wrote:
>>> --- a/automation/eclair_analysis/ECLAIR/deviations.ecl
>>> +++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
>>> @@ -565,6 +565,10 @@ of this macro do not lead to developer confusion, and can thus be deviated."
>>>   -config=MC3R1.R20.7,reports+={safe, "any_area(any_loc(any_exp(macro(^count_args_$))))"}
>>>   -doc_end
>>>   
>>> +-doc_begin="The expansion of an argument surrounded by tokens '{', '}' and ';' is safe."
>>> +-config=MC3R1.R20.7,expansion_context+={safe, "left_right(^[\\{;]$,^[;\\}]$)"}
>>> +-doc_end
>>
>> Not the least because this is quite a bit wider than ...
>>
>>> --- a/xen/include/xen/bitmap.h
>>> +++ b/xen/include/xen/bitmap.h
>>> @@ -103,13 +103,10 @@ extern int bitmap_allocate_region(unsigned long *bitmap, int pos, int order);
>>>   #define bitmap_switch(nbits, zero, small, large)			  \
>>>   	unsigned int n__ = (nbits);					  \
>>>   	if (__builtin_constant_p(nbits) && !n__) {			  \
>>> -		/* SAF-7-safe Rule 20.7 non-parenthesized macro argument */ \
>>>   		zero;							  \
>>>   	} else if (__builtin_constant_p(nbits) && n__ <= BITS_PER_LONG) { \
>>> -		/* SAF-7-safe Rule 20.7 non-parenthesized macro argument */ \
>>>   		small;							  \
>>>   	} else {							  \
>>> -		/* SAF-7-safe Rule 20.7 non-parenthesized macro argument */ \
>>>   		large;							  \
>>>   	}
>>
>> ... what's needed here, I wonder if we're not opening up avenues to
>> problems by generally permitting that pattern. Plus in the description
>> I'm missing a statement to the effect of why this is (always) safe.
> 
> The rational of the rule is that if a macro argument expands to an
> expression, there may be problems related to operator precedence, e.g.:
> 
> #define A(x, y) x * y
> 
> A(1+1, 2+2) will expand to: 1+1 * 2+2
> 
> Yes, the deviation is more general and wider than what is needed for
> the specific case but it is safe: if the expanded argument is between
> one of the aforementioned tokens, then there are no operators involved
> and no precedence issues.
> 
> I can add some details in a v2.

Please do,taking into consideration also language extensions that we use,
e.g. the statements-as-expressions one (where figure braces exist inside
an expression).

Jan

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