Re: [PATCH] x86/emul: Work around MISRA R13.2 complaint

[Jan Beulich <jbeulich@xxxxxxxx>]

On 10.05.2025 02:18, Andrew Cooper wrote:
> Rule 13.2 states: "The value of an expression and its persistent side effects
> shall be the same under all permitted evaluation orders".
> 
> Eclair complains about a Rule 13.2 violations because validate_far_branch()
> assigns to rc,

Followed by "goto", i.e. not taking the path to ...

> and the entirety of commit_far_branch() is also assigned to rc.

... that assignment. This pretty clearly looks like a tool shortcoming to
me, and I think it would be a good idea to ...

> --- a/xen/arch/x86/x86_emulate/x86_emulate.c
> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
> @@ -333,12 +333,14 @@ do {                                                    
>                 \
>                                : (ip) > (cs)->limit, X86_EXC_GP, 0);     \
>  })
>  
> -#define commit_far_branch(cs, newip) ({                                 \
> -    validate_far_branch(cs, newip);                                     \
> -    _regs.r(ip) = (newip);                                              \
> -    singlestep = _regs.eflags & X86_EFLAGS_TF;                          \
> -    ops->write_segment(x86_seg_cs, cs, ctxt);                           \
> -})
> +#define commit_far_branch(cs, newip) (                                  \
> +        ({                                                              \
> +            validate_far_branch(cs, newip);                             \
> +            _regs.r(ip) = (newip);                                      \
> +            singlestep = _regs.eflags & X86_EFLAGS_TF;                  \
> +        }),                                                             \
> +        ops->write_segment(x86_seg_cs, cs, ctxt)                        \
> +    )

... add a brief comment here clarifying why this odd a statement is used.

Jan