Re: [PATCH] docs/misra: new rules addition

[Jan Beulich <jbeulich@xxxxxxxx>]

On 08.06.2023 13:02, Roberto Bagnara wrote:
> On 07/06/23 23:53, Stefano Stabellini wrote:
>> On Wed, 7 Jun 2023, Jan Beulich wrote:
>>>> +   * - `Rule 5.6 
>>>> <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_05_06.c>`_
>>>> +     - Required
>>>> +     - A typedef name shall be a unique identifier
>>>> +     -
>>>
>>> Considering that the rule requires uniqueness across the entire code
>>> base (and hence precludes e.g. two functions having identically named
>>> local typedefs), I'm a little puzzled this was adopted. I for one
>>> question that a use like the one mentioned is really at risk of being
>>> confusing. Instead I think that the need to change at least one of
>>> the names is at risk of making the code less readable then, even if
>>> ever so slightly. (All of this said - I don't know if we have any
>>> violations of this rule.)
>>
>> I don't think we have many local typedefs and I think we have only few
>> violations if I remember right. I'll let Roberto confirm how many. This
>> rule was considered not a difficult rule (some difficult rules were
>> found, namely 2.1, 5.5 and 7.4.)
> 
> There currently are 30 violations for ARM64:
> 
> - some involve a typedef module_name (in the call it was said this should
>    be renamed module_name_t, which will solve the issue);
> - most concern repeated typedefs (UINT64 and similar) which are repeated
>    in xen/arch/arm/include/asm/arm64/efibind.h
>    and xen/include/acpi/actypes.h
> - ret_t and phys_addr_t are also redefined in a couple of places.
> 
> There are 90 violations for X86_64, for the same reasons, plus
> 
> - another set of typedefs for basic types (such as u8);
> - repeated typedefs for things like guest_l1e_t in the same header file:
> 
> xen/arch/x86/include/asm/guest_pt.h:60.39-60.49:
> for program `xen/.xen-syms.0', the identifier for typedef `guest_l1e_t' is 
> reused
> xen/arch/x86/include/asm/guest_pt.h:128.22-128.32:
> for program `xen/.xen-syms.0', the identifier for typedef `guest_l1e_t' is 
> reused
> 
> The indicated lines read as follows:
> 
> typedef struct { guest_intpte_t l1; } guest_l1e_t;
> typedef l1_pgentry_t guest_l1e_t;

So this is an example where I don't think we can sensibly do away with the
re-use of the same typedef name: We use it so we can build the same source
files multiple ways, dealing with different paging modes guests may be in.

Jan