Re: [PATCH 2/2] xen/arm: Fix MISRA regression on R1.1, flexible array member not at the end

[Nicola Vetrini <nicola.vetrini@bugseng.com>]

On 2024-04-30 13:09, Luca Fancellu wrote:
> Commit 2209c1e35b47 ("xen/arm: Introduce a generic way to access memory
> bank structures") introduced a MISRA regression for Rule 1.1 because a
> flexible array member is introduced in the middle of a struct, 
> furthermore
> this is using a GCC extension that is going to be deprecated in GCC 14 
> and
> a warning to identify such cases will be present
> (-Wflex-array-member-not-at-end) to identify such cases.
> 
> In order to fix this issue, use the macro __struct_group to create a
> structure 'struct membanks_hdr' which will hold the common data among
> structures using the 'struct membanks' interface.
> 
> Modify the 'struct shared_meminfo' and 'struct meminfo' to use this new
> structure, effectively removing the flexible array member from the 
> middle
> of the structure and modify the code accessing the .common field to use
> the macro container_of to maintain the functionality of the interface.
> 
> Given this change, container_of needs to be supplied with a type and so
> the macro 'kernel_info_get_mem' inside arm/include/asm/kernel.h can't 
> be
> an option since it uses const and non-const types for struct membanks, 
> so
> introduce two static inline, one of which will keep the const 
> qualifier.
> 
> Given the complexity of the interface, which carries a lot of benefit 
> but
> on the other hand could be prone to developer confusion if the access 
> is
> open-coded, introduce two static inline helper for the
> 'struct kernel_info' .shm_mem member and get rid the open-coding
> shm_mem.common access.
> 
> Fixes: 2209c1e35b47 ("xen/arm: Introduce a generic way to access memory 
> bank structures")
> Signed-off-by: Luca Fancellu <luca.fancellu@arm.com>
> ---
>  xen/arch/arm/acpi/domain_build.c        |  2 +-
>  xen/arch/arm/domain_build.c             |  6 +++---
>  xen/arch/arm/include/asm/kernel.h       | 11 ++++++++++-
>  xen/arch/arm/include/asm/setup.h        | 18 ++++++++++--------
>  xen/arch/arm/include/asm/static-shmem.h | 12 ++++++++++++
>  xen/arch/arm/static-shmem.c             | 19 +++++++++----------
>  6 files changed, 45 insertions(+), 23 deletions(-)
> 

 From a MISRA perspective the regression on R1.1 is resolved (see [1]).

[1] https://gitlab.com/xen-project/patchew/xen/-/jobs/6748211368

-- 
Nicola Vetrini, BSc
Software Engineer, BUGSENG srl (https://bugseng.com)