Re: [PATCH] generic/altp2m: address violations of MISRA C Rule 2.1

[Dmytro Prokopchuk1 <dmytro_prokopchuk1@xxxxxxxx>]

Hello, Jan

On 4/10/26 09:04, Jan Beulich wrote:
> On 09.04.2026 19:37, Dmytro Prokopchuk1 wrote:
>> MISRA C Rule 2.1 states: "A project shall not contain unreachable code".
>>
>> In certain build configurations,
> 
> Can you give an example where ...
If CONFIG_VM_EVENT is enabled on ARM.
> 
>> the function 'altp2m_vcpu_idx()' is defined
>> as an inline function that contains the 'BUG()' macro. This resulted in a
>> violation because the 'BUG()' macro makes the function non-returning.
>>
>> To ensure compliance with MISRA C Rule 2.1, this patch removes the inline
>> function implementation and its BUG()-based unreachable code. It is replaced
>> with an unconditional function declaration for 'altp2m_vcpu_idx()'.
> 
> ... a declaration is needed? The sole non-x86 reference I see is from
Yes, declaration is needed. The file 'common/monitor.c' contains a usage 
of the 'altp2m_vcpu_idx()' and compiler must see it to avoid "error: 
implicit declaration of function ‘altp2m_vcpu_idx’".
> common/monitor.c, and the sole relevant Kconfig option I can spot is
> VM_EVENT. When that's off, the file won't be built at all.
But when 'CONFIG_VM_EVENT=y' this file is compiled on ARM.
> 
> Further, BUG() and a few more constructs have a dedicated deviation
> already in place. I don't mind a useless function to be shrunk (or, as
> per above, perhaps even dropped), but the justification then needs to
> be different.
Well, with Stefano's comment regarding return type, the commit subject 
and message could be rewritten like:

generic/altp2m: align and simplify altp2m_vcpu_idx()

The return type of 'altp2m_vcpu_idx()' in the generic altp2m.h header is
currently 'unsigned int', which is inconsistent with its 'uint16_t'
return type on x86 and the 'altp2m_idx' member of the monitor structures.

To fix this type inconsistency and simplify the header, this patch
replaces the static inline implementation of 'altp2m_vcpu_idx()' 
(contained a BUG() stub) with a simple function declaration returning
uint16_t.

For architectures using the generic altp2m.h header (such as ARM when
CONFIG_VM_EVENT is enabled), common code calls to 'altp2m_vcpu_idx()' in 
common/monitor.c are guarded by 'altp2m_active()', which
statically returns 'false'. The compiler's DCE will optimize out these 
calls, avoiding any linker issues for the missing definition.

> 
> Jan

BR, Dmytro.