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
