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


  • To: Federico Serafini <federico.serafini@xxxxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Fri, 30 Aug 2024 11:10:47 +0200
  • Autocrypt: addr=jbeulich@xxxxxxxx; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL
  • Cc: consulting@xxxxxxxxxxx, Simone Ballarin <simone.ballarin@xxxxxxxxxxx>, Doug Goldstein <cardoe@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Fri, 30 Aug 2024 09:10:55 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

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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