[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [PATCH v2] misra: add deviation for MISRA C Rule 11.3
- To: Dmytro Prokopchuk1 <dmytro_prokopchuk1@xxxxxxxx>
- From: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
- Date: Fri, 26 Sep 2025 09:49:08 +0200
- Arc-authentication-results: i=1; bugseng.com; arc=none smtp.remote-ip=162.55.131.47
- Arc-message-signature: i=1; d=bugseng.com; s=openarc; a=rsa-sha256; c=relaxed/relaxed; t=1758872948; h=DKIM-Signature:MIME-Version:Date:From:To:Cc:Subject:In-Reply-To: References:Message-ID:X-Sender:Organization:Content-Type: Content-Transfer-Encoding; bh=hOX7BXjqXFIc87ZFW5RPol29CzZmaqU6Ty3bcp9Rj24=; b=pG0eS/YCx5btoq7YWTFj8h7cDTnrFfyrb1XNBwuNUzrx4bVhbOLeYkSQfldUr/iD8VMy 0PTLWn930BfE1jGupF7wEqAX/f8Cto8CxA4J7hxha8vXO4jEwNLGQaMCxr3glScnp4Mpf 8kzDobdo1fdJdxa68dDTGxE4ljeqLQp6Va/YyFw2pmNcJbZ7cu3xpG95UK5EbPthtmdVx Gh3/caTsFboDevKMCNPGoWNO3whDJuZrWVgdWLp8taazo7X4zfdVbylJT8+W9wjtxFHwI zHNWH/1GdHvNVRbDetcBhawLgdx930RPmU7q2Q9AWKlJkAkZrarDKQ4woAffnz133gPON etMWvSEUPaJlVbHb3VAUVbCI7kzR1OLWgL87sZz21zlhbMNhJxWTaPu1XAeogi5C4D06R 7nfvxTjbY//sE5DzcywVxdm3MCCZuwKBcxY8F+h0mas6j5hfLAd+/Zb0yHdAoxfiCdOy9 cauuI6nmKMqXmpHG47mqvz4k3nCkXU5bm2zPOeKQHfJifIv5hG6hdB5mveo2HhQvT1lIt CTa8InMXFW3rB/Brp2EQbCmQy82hOm7wjeucVkkCL7L8QW+R/fur12KMtWCzZOr5/m3ds J6YQUQazJ0NptmqJTjVGKcLDcKpQHIl2JzbSi/JvxljlhAxXJBrnkSnFC/5lFXc=
- Arc-seal: i=1; d=bugseng.com; s=openarc; a=rsa-sha256; cv=none; t=1758872948; b=hxFbrJg0HD1mrPZrjhJEMHtfhfDkKhaIP4pFSe8syEAicIOsWZEJUvbUPXAn+7nUraXB JaC29VkOzt0h2NV6FWdN5NJRh+HdwOPxYky6nsCoTJCZ+XX3vvqODkfk8rr6NsOcjflqz ls9s36ZmQZ6uUlns5PBtOoGSk7hTK4daNJxxQSuym/CWHaDAvBILvt0Xcbs68eTQe4UOR 4zm/FmNopRKooKo9nbP/J4PzoxXAin9nmFkgc5bKc5ES66X1ahRYnCkAlLIbrbr/nxp3I +z8Z5mmgGoXwbTRrdwGSXKMW7P9fpcEUT7X36txafnWhlvNZ35y/e+KK0fNR+1R3WvGiy 95ofcW9xTWb3WXRbpHdEFwbA7lFinsju8D8i/DkjQP+itHCxvUjad4t8ItkRyZ1bneoP+ QLoC2ExL4YPfRBrAl1gJoLnhKMUKmpMr90LgRxZrzCtRDkn2WRtA4rwi/bqr23DLFrKEH hMGeUQ7H8zfQZ/otN4+Ig6UAwgLRtoehjbR0WKTZvuURpbOkt0+u/Qa4AO6VP3i181hbc lRzl6H8L2JOTNY+wB7ddHt+hfSYBx0yDHRC7iTezvN7DP83cMDaYglngAIQwfadxH+5OA tm5UwmeInxQ1jvZWp+YeInUORXPOhNw3Ou25CTrOU/Q+WR2V/p8PSAFMlpyJ/ls=
- Authentication-results: bugseng.com; arc=none smtp.remote-ip=162.55.131.47
- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Doug Goldstein <cardoe@xxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, Jan Beulich <jbeulich@xxxxxxxx>
- Delivery-date: Fri, 26 Sep 2025 07:49:21 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 2025-09-25 21:11, Dmytro Prokopchuk1 wrote:
On 8/25/25 13:23, Jan Beulich wrote:
On 24.08.2025 19:27, Dmytro Prokopchuk1 wrote:
MISRA C Rule 11.3 states: "A cast shall not be performed between a
pointer
to object type and a pointer to a different object type."
Violations of this rule arise due to the 'container_of()' macro,
which casts
a member of a structure to its containing structure:
container_of(ptr, type, member) ({ \
typeof_field(type, member) *__mptr = (ptr); \
(type *)( (char *)__mptr - offsetof(type,member) );})
The 'container_of()' macro is safe because it relies on the
standardized and
well-defined 'offsetof()' macro to calculate the memory address of
the
containing structure, while assuming proper alignment and ensuring no
undefined behavior, provided that the input pointer is valid and
points to
the specified member.
I may have said so before: This all reads okay to me, just that I'm
unsure
it would actually be convincing to an assessor. The "provided that
..." is
a pretty strong requirement, which isn't overly hard to get wrong.
Stefano,
Nicola - what's your take here?
Jan
Stefano, Nicola,
gentle reminder.
Dmytro.
The fact that you can't guarantee that the pointer you receive is
aligned was the main reason why I didn't already introduce such a
deviation in the first place. Now, as Stefano pointed out unaligned
accessed are largely ok on ARM and x86, with the exception on MMIO
pointers (hard fault) and some niche cases in x86 which probably don't
matter for Xen dealing with vectorized data types. So the crucial point
(not just for this specific deviation) is ensuring that pointer are
properly aligned when it matters, which in this case is the same as
making sure that "ptr" indeed points to a struct member. What might be a
convincing argument is to have sufficient testing and sanitizers (ASAN
mostly helps here) to show that this assumption is met with some degree
of confidence.
--
Nicola Vetrini, B.Sc.
Software Engineer
BUGSENG (https://bugseng.com)
LinkedIn: https://www.linkedin.com/in/nicola-vetrini-a42471253
|
