Re: [PATCH v1 1/3] x86: x86_emulate: address violations of MISRA C Rule 19.1

[Jan Beulich <jbeulich@xxxxxxxx>]

On 26.04.2025 01:42, victorm.lira@xxxxxxx wrote:
> From: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
> 
> Rule 19.1 states: "An object shall not be assigned or copied
> to an overlapping object". Since the "call" and "compat_call" are

Was this taken from patch 2 without editing?

> --- a/xen/arch/x86/x86_emulate/x86_emulate.c
> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
> @@ -526,9 +526,19 @@ static inline void put_loop_count(
>           */                                                             \
>          if ( !amd_like(ctxt) && mode_64bit() && ad_bytes == 4 )         \
>          {                                                               \
> +            uint64_t tmp;                                               \
> +                                                                        \
>              _regs.r(cx) = 0;                                            \
> -            if ( extend_si ) _regs.r(si) = _regs.esi;                   \
> -            if ( extend_di ) _regs.r(di) = _regs.edi;                   \
> +            if ( extend_si )                                            \
> +            {                                                           \
> +                tmp = _regs.esi;                                        \
> +                _regs.r(si) = tmp;                                      \
> +            }                                                           \
> +            if ( extend_di )                                            \
> +            {                                                           \
> +                tmp = _regs.edi;                                        \
> +                _regs.r(di) = tmp;                                      \
> +            }                                                           \

See commit 7225f13aef03 for how we chose to address similar issues elsewhere
in the emulator. I think we want to be consistent there. This will then also
eliminate ...

> @@ -2029,7 +2039,12 @@ x86_emulate(
>          switch ( op_bytes )
>          {
>          case 2: _regs.ax = (int8_t)_regs.ax; break; /* cbw */
> -        case 4: _regs.r(ax) = (uint32_t)(int16_t)_regs.ax; break; /* cwde */
> +        case 4:
> +            {
> +                uint32_t tmp = (uint32_t)(int16_t)_regs.ax;
> +                _regs.r(ax) = tmp;
> +                break; /* cwde */
> +            }

... the odd brace placement here, as well as the inconsistency in the types
you used for the temporary variables (both really could have been unsigned
int; no need for a fixed-width type).

Jan