Re: [XEN PATCH v3 07/12] x86/hvm: address violations of MISRA C Rule 16.3

[Jan Beulich <jbeulich@xxxxxxxx>]

On 26.06.2024 11:28, Federico Serafini wrote:
> @@ -2798,11 +2800,12 @@ void hvm_emulate_one_vm_event(enum emul_kind kind, 
> unsigned int trapnr,
>          hvio->mmio_insn_bytes = sizeof(hvio->mmio_insn);
>          memcpy(hvio->mmio_insn, curr->arch.vm_event->emul.insn.data,
>                 hvio->mmio_insn_bytes);
> +        fallthrough;
>      }
> -    /* Fall-through */
>      default:

Can you clarify for me please whether this arrangement actually helps?
I'm pretty sure it'll result in a Coverity complaint, as my understanding
is that for them the marker (comment or pseudo-keyword) has to immediately
precede the subsequent label. IOW even if you confirmed that Eclair is
smarter in this regard, it may still need converting to

        hvio->mmio_insn_bytes = sizeof(hvio->mmio_insn);
        memcpy(hvio->mmio_insn, curr->arch.vm_event->emul.insn.data,
               hvio->mmio_insn_bytes);
    }
        fallthrough;
    default:

> --- a/xen/arch/x86/hvm/hypercall.c
> +++ b/xen/arch/x86/hvm/hypercall.c
> @@ -111,6 +111,7 @@ int hvm_hypercall(struct cpu_user_regs *regs)
>      case 8:
>          eax = regs->rax;
>          /* Fallthrough to permission check. */
> +        fallthrough;
>      case 4:
>      case 2:
>          if ( currd->arch.monitor.guest_request_userspace_enabled &&

Arguably the comment could then be dropped in exchange. Yet I won't
insist on you doing so (and others may also disagree).

Jan