Re: [XEN PATCH v2] arm64/vfp: address MISRA C:2012 Dir 4.3

[Michal Orzel <michal.orzel@xxxxxxx>]

Hi Nicola,

On 24/08/2023 09:37, Nicola Vetrini wrote:
> 
> 
> Directive 4.3 prescribes the following:
> "Assembly language shall be encapsulated and isolated",
> on the grounds of improved readability and ease of maintenance.
> 
> A static inline function is the chosen encapsulation mechanism.
> 
> No functional change.
> 
> Signed-off-by: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
> ---
> Changes in v2:
> - Switched to a static inline function
> ---
>  xen/arch/arm/arm64/vfp.c | 78 ++++++++++++++++++++++------------------
>  1 file changed, 44 insertions(+), 34 deletions(-)
> 
> diff --git a/xen/arch/arm/arm64/vfp.c b/xen/arch/arm/arm64/vfp.c
> index 2d0d7c2e6ddb..5c884380ee42 100644
> --- a/xen/arch/arm/arm64/vfp.c
> +++ b/xen/arch/arm/arm64/vfp.c
> @@ -4,6 +4,48 @@
>  #include <asm/vfp.h>
>  #include <asm/arm64/sve.h>
> 
> +static inline void save_state(uint64_t *fpregs)
> +{
> +    asm volatile("stp q0, q1, [%1, #16 * 0]\n\t"
> +                 "stp q2, q3, [%1, #16 * 2]\n\t"
> +                 "stp q4, q5, [%1, #16 * 4]\n\t"
> +                 "stp q6, q7, [%1, #16 * 6]\n\t"
> +                 "stp q8, q9, [%1, #16 * 8]\n\t"
> +                 "stp q10, q11, [%1, #16 * 10]\n\t"
> +                 "stp q12, q13, [%1, #16 * 12]\n\t"
> +                 "stp q14, q15, [%1, #16 * 14]\n\t"
> +                 "stp q16, q17, [%1, #16 * 16]\n\t"
> +                 "stp q18, q19, [%1, #16 * 18]\n\t"
> +                 "stp q20, q21, [%1, #16 * 20]\n\t"
> +                 "stp q22, q23, [%1, #16 * 22]\n\t"
> +                 "stp q24, q25, [%1, #16 * 24]\n\t"
> +                 "stp q26, q27, [%1, #16 * 26]\n\t"
> +                 "stp q28, q29, [%1, #16 * 28]\n\t"
> +                 "stp q30, q31, [%1, #16 * 30]\n\t"
> +                 : "=Q" (*fpregs) : "r" (fpregs));
> +}
> +
> +static inline void restore_state(uint64_t *fpregs)
This can be const as you are loading data from fpregs into registers

> +{
> +    asm volatile("ldp q0, q1, [%1, #16 * 0]\n\t"
> +                 "ldp q2, q3, [%1, #16 * 2]\n\t"
> +                 "ldp q4, q5, [%1, #16 * 4]\n\t"
> +                 "ldp q6, q7, [%1, #16 * 6]\n\t"
> +                 "ldp q8, q9, [%1, #16 * 8]\n\t"
> +                 "ldp q10, q11, [%1, #16 * 10]\n\t"
> +                 "ldp q12, q13, [%1, #16 * 12]\n\t"
> +                 "ldp q14, q15, [%1, #16 * 14]\n\t"
> +                 "ldp q16, q17, [%1, #16 * 16]\n\t"
> +                 "ldp q18, q19, [%1, #16 * 18]\n\t"
> +                 "ldp q20, q21, [%1, #16 * 20]\n\t"
> +                 "ldp q22, q23, [%1, #16 * 22]\n\t"
> +                 "ldp q24, q25, [%1, #16 * 24]\n\t"
> +                 "ldp q26, q27, [%1, #16 * 26]\n\t"
> +                 "ldp q28, q29, [%1, #16 * 28]\n\t"
> +                 "ldp q30, q31, [%1, #16 * 30]\n\t"
> +                 : : "Q" (*fpregs), "r" (fpregs));
> +}
> +
>  void vfp_save_state(struct vcpu *v)
>  {
>      if ( !cpu_has_fp )
> @@ -13,23 +55,7 @@ void vfp_save_state(struct vcpu *v)
>          sve_save_state(v);
>      else
>      {
No need for brackets
> -        asm volatile("stp q0, q1, [%1, #16 * 0]\n\t"
> -                     "stp q2, q3, [%1, #16 * 2]\n\t"
> -                     "stp q4, q5, [%1, #16 * 4]\n\t"
> -                     "stp q6, q7, [%1, #16 * 6]\n\t"
> -                     "stp q8, q9, [%1, #16 * 8]\n\t"
> -                     "stp q10, q11, [%1, #16 * 10]\n\t"
> -                     "stp q12, q13, [%1, #16 * 12]\n\t"
> -                     "stp q14, q15, [%1, #16 * 14]\n\t"
> -                     "stp q16, q17, [%1, #16 * 16]\n\t"
> -                     "stp q18, q19, [%1, #16 * 18]\n\t"
> -                     "stp q20, q21, [%1, #16 * 20]\n\t"
> -                     "stp q22, q23, [%1, #16 * 22]\n\t"
> -                     "stp q24, q25, [%1, #16 * 24]\n\t"
> -                     "stp q26, q27, [%1, #16 * 26]\n\t"
> -                     "stp q28, q29, [%1, #16 * 28]\n\t"
> -                     "stp q30, q31, [%1, #16 * 30]\n\t"
> -                     : "=Q" (*v->arch.vfp.fpregs) : "r" 
> (v->arch.vfp.fpregs));
> +        save_state(v->arch.vfp.fpregs);
>      }
> 
>      v->arch.vfp.fpsr = READ_SYSREG(FPSR);
> @@ -47,23 +73,7 @@ void vfp_restore_state(struct vcpu *v)
>          sve_restore_state(v);
>      else
>      {
No need for brackets
> -        asm volatile("ldp q0, q1, [%1, #16 * 0]\n\t"
> -                     "ldp q2, q3, [%1, #16 * 2]\n\t"
> -                     "ldp q4, q5, [%1, #16 * 4]\n\t"
> -                     "ldp q6, q7, [%1, #16 * 6]\n\t"
> -                     "ldp q8, q9, [%1, #16 * 8]\n\t"
> -                     "ldp q10, q11, [%1, #16 * 10]\n\t"
> -                     "ldp q12, q13, [%1, #16 * 12]\n\t"
> -                     "ldp q14, q15, [%1, #16 * 14]\n\t"
> -                     "ldp q16, q17, [%1, #16 * 16]\n\t"
> -                     "ldp q18, q19, [%1, #16 * 18]\n\t"
> -                     "ldp q20, q21, [%1, #16 * 20]\n\t"
> -                     "ldp q22, q23, [%1, #16 * 22]\n\t"
> -                     "ldp q24, q25, [%1, #16 * 24]\n\t"
> -                     "ldp q26, q27, [%1, #16 * 26]\n\t"
> -                     "ldp q28, q29, [%1, #16 * 28]\n\t"
> -                     "ldp q30, q31, [%1, #16 * 30]\n\t"
> -                     : : "Q" (*v->arch.vfp.fpregs), "r" 
> (v->arch.vfp.fpregs));
> +        restore_state(v->arch.vfp.fpregs);
>      }
> 
>      WRITE_SYSREG(v->arch.vfp.fpsr, FPSR);

Apart from that (up to maintainers if it can be done on commit):
Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>

~Michal