Re: [XEN PATCH 4/6] x86emul: address violations of MISRA C Rule 20.7

[Jan Beulich <jbeulich@xxxxxxxx>]

On 11.06.2024 17:53, Nicola Vetrini wrote:
> MISRA C Rule 20.7 states: "Expressions resulting from the expansion
> of macro parameters shall be enclosed in parentheses". Therefore, some
> macro definitions should gain additional parentheses to ensure that all
> current and future users will be safe with respect to expansions that
> can possibly alter the semantics of the passed-in macro parameter.
> 
> No functional change.
> 
> Signed-off-by: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
> ---
> These local helpers could in principle be deviated, but the readability
> and functionality are essentially unchanged by complying with the rule,
> so I decided to modify the macro definition as the preferred option.

Well, yes, but ...

> --- a/xen/arch/x86/x86_emulate/x86_emulate.c
> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
> @@ -2255,7 +2255,7 @@ x86_emulate(
>          switch ( modrm_reg & 7 )
>          {
>  #define GRP2(name, ext) \
> -        case ext: \
> +        case (ext): \
>              if ( ops->rmw && dst.type == OP_MEM ) \
>                  state->rmw = rmw_##name; \
>              else \
> @@ -8611,7 +8611,7 @@ int x86_emul_rmw(
>              unsigned long dummy;
>  
>  #define XADD(sz, cst, mod) \
> -        case sz: \
> +        case (sz): \
>              asm ( "" \
>                    COND_LOCK(xadd) " %"#mod"[reg], %[mem]; " \
>                    _POST_EFLAGS("[efl]", "[msk]", "[tmp]") \

... this is really nitpicky of the rule / tool. What halfway realistic
ways do you see to actually misuse these macros? What follows the "case"
keyword is just an expression; no precedence related issues are possible.

Jan