Re: [XEN PATCH for-4.19] xen/bitmap: amend MISRA C deviation for Rule 20.7

[Jan Beulich <jbeulich@xxxxxxxx>]

On 09.07.2024 11:34, Nicola Vetrini wrote:
> As noticed in the gitlab analyses, deviating bitmap_switch
> for Rule 20.7 in this way does not work for ECLAIR.
> 
> Instead, the deviation should be put in the macro invocation.

Why is this? I ask in particular because ...

> --- a/xen/include/xen/bitmap.h
> +++ b/xen/include/xen/bitmap.h
> @@ -103,18 +103,16 @@ 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;                                                    \
>       }
>  
>  static inline void bitmap_zero(unsigned long *dst, unsigned int nbits)
>  {
> +     /* SAF-7-safe Rule 20.7 non-parenthesized macro argument */
>       bitmap_switch(nbits,,
>               *dst = 0UL,
>               memset(dst, 0, bitmap_bytes(nbits)));
> @@ -139,6 +137,7 @@ static inline void bitmap_fill(unsigned long *dst, 
> unsigned int nbits)
>  static inline void bitmap_copy(unsigned long *dst, const unsigned long *src,
>                       unsigned int nbits)
>  {
> +        /* SAF-7-safe Rule 20.7 non-parenthesized macro argument */
>       bitmap_switch(nbits,,
>               *dst = *src,
>               memcpy(dst, src, bitmap_bytes(nbits)));
> @@ -147,6 +146,7 @@ static inline void bitmap_copy(unsigned long *dst, const 
> unsigned long *src,
>  static inline void bitmap_and(unsigned long *dst, const unsigned long *src1,
>                       const unsigned long *src2, unsigned int nbits)
>  {
> +     /* SAF-7-safe Rule 20.7 non-parenthesized macro argument */
>       bitmap_switch(nbits,,
>               *dst = *src1 & *src2,
>               __bitmap_and(dst, src1, src2, nbits));
> @@ -155,6 +155,7 @@ static inline void bitmap_and(unsigned long *dst, const 
> unsigned long *src1,
>  static inline void bitmap_or(unsigned long *dst, const unsigned long *src1,
>                       const unsigned long *src2, unsigned int nbits)
>  {
> +     /* SAF-7-safe Rule 20.7 non-parenthesized macro argument */
>       bitmap_switch(nbits,,
>               *dst = *src1 | *src2,
>               __bitmap_or(dst, src1, src2, nbits));
> @@ -163,6 +164,7 @@ static inline void bitmap_or(unsigned long *dst, const 
> unsigned long *src1,
>  static inline void bitmap_xor(unsigned long *dst, const unsigned long *src1,
>                       const unsigned long *src2, unsigned int nbits)
>  {
> +     /* SAF-7-safe Rule 20.7 non-parenthesized macro argument */
>       bitmap_switch(nbits,,
>               *dst = *src1 ^ *src2,
>               __bitmap_xor(dst, src1, src2, nbits));
> @@ -171,6 +173,7 @@ static inline void bitmap_xor(unsigned long *dst, const 
> unsigned long *src1,
>  static inline void bitmap_andnot(unsigned long *dst, const unsigned long 
> *src1,
>                       const unsigned long *src2, unsigned int nbits)
>  {
> +     /* SAF-7-safe Rule 20.7 non-parenthesized macro argument */
>       bitmap_switch(nbits,,
>               *dst = *src1 & ~*src2,
>               __bitmap_andnot(dst, src1, src2, nbits));
> @@ -179,6 +182,7 @@ static inline void bitmap_andnot(unsigned long *dst, 
> const unsigned long *src1,
>  static inline void bitmap_complement(unsigned long *dst, const unsigned long 
> *src,
>                       unsigned int nbits)
>  {
> +     /* SAF-7-safe Rule 20.7 non-parenthesized macro argument */
>       bitmap_switch(nbits,,
>               *dst = ~*src & BITMAP_LAST_WORD_MASK(nbits),
>               __bitmap_complement(dst, src, nbits));
> @@ -187,6 +191,7 @@ static inline void bitmap_complement(unsigned long *dst, 
> const unsigned long *sr
>  static inline int bitmap_equal(const unsigned long *src1,
>                       const unsigned long *src2, unsigned int nbits)
>  {
> +     /* SAF-7-safe Rule 20.7 non-parenthesized macro argument */
>       bitmap_switch(nbits,
>               return -1,
>               return !((*src1 ^ *src2) & BITMAP_LAST_WORD_MASK(nbits)),
> @@ -196,6 +201,7 @@ static inline int bitmap_equal(const unsigned long *src1,
>  static inline int bitmap_intersects(const unsigned long *src1,
>                       const unsigned long *src2, unsigned int nbits)
>  {
> +     /* SAF-7-safe Rule 20.7 non-parenthesized macro argument */
>       bitmap_switch(nbits,
>               return -1,
>               return ((*src1 & *src2) & BITMAP_LAST_WORD_MASK(nbits)) != 0,
> @@ -205,6 +211,7 @@ static inline int bitmap_intersects(const unsigned long 
> *src1,
>  static inline int bitmap_subset(const unsigned long *src1,
>                       const unsigned long *src2, unsigned int nbits)
>  {
> +     /* SAF-7-safe Rule 20.7 non-parenthesized macro argument */
>       bitmap_switch(nbits,
>               return -1,
>               return !((*src1 & ~*src2) & BITMAP_LAST_WORD_MASK(nbits)),
> @@ -213,6 +220,7 @@ static inline int bitmap_subset(const unsigned long *src1,
>  
>  static inline int bitmap_empty(const unsigned long *src, unsigned int nbits)
>  {
> +     /* SAF-7-safe Rule 20.7 non-parenthesized macro argument */
>       bitmap_switch(nbits,
>               return -1,
>               return !(*src & BITMAP_LAST_WORD_MASK(nbits)),
> @@ -221,6 +229,7 @@ static inline int bitmap_empty(const unsigned long *src, 
> unsigned int nbits)
>  
>  static inline int bitmap_full(const unsigned long *src, unsigned int nbits)
>  {
> +     /* SAF-7-safe Rule 20.7 non-parenthesized macro argument */
>       bitmap_switch(nbits,
>               return -1,
>               return !(~*src & BITMAP_LAST_WORD_MASK(nbits)),

... having the same comment on every invocation is naturally quite a bit
less desirable. So far I was under the impression that macro-specific
deviations can be dealt with by marking the macro definition accordingly.
I've been assuming this is a general pattern. If it isn't, would you
please first clarify what Eclair's specific requirements are for a SAF
marker to take effect when involving a macro?

Jan