Re: [PATCH] x86/gen-cpuid: avoid violations of Misra rule 1.3

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 02/08/2023 10:43 am, Jan Beulich wrote:
> Structures or unions without any named members aren't liked by Misra
> (nor the C standard). Avoid emitting such for leaves without any known
> bits.
>
> At this occasion also add the script to the X86 section in ./MAINTAINERS.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -601,6 +601,7 @@ F:        xen/arch/x86/
>  F:   xen/include/public/arch-x86/
>  F:   xen/include/xen/lib/x86
>  F:   xen/lib/x86
> +F:   xen/tools/gen-cpuid.py
>  F:   tools/firmware/hvmloader/
>  F:   tools/firmware/rombios/
>  F:   tools/firmware/vgabios/
> --- a/xen/tools/gen-cpuid.py
> +++ b/xen/tools/gen-cpuid.py
> @@ -367,6 +367,7 @@ def crunch_numbers(state):
>      for word in range(state.nr_entries):
>  
>          names = []
> +        empty = 1
>          for bit in range(32):
>  
>              name = state.names.get(word * 32 + bit, "")
> @@ -380,9 +381,15 @@ def crunch_numbers(state):
>              if name in ("APIC", "OSXSAVE", "OSPKE"):
>                  name = ""
>  
> +            if name:
> +                empty = 0
> +
>              names.append(name.lower())
>  
> -        state.bitfields.append("bool " + ":1, ".join(names) + ":1")
> +        if empty:
> +            state.bitfields.append("unsigned int empty_" + str(word) + ":32")
> +        else:
> +            state.bitfields.append("bool " + ":1, ".join(names) + ":1")

There's no need for the extra empty variable (this is python, not C).

if any(names):
    state.bitfields.append("bool " + ":1, ".join(names) + ":1")
else:
    state.bitfields.append("uint32_t empty_%s" % (word, ))

But there's a related bug later in the script which MISRA won't notice
unless it happens to run on the cset boundary introducing a new leaf.

I'll see about doing a patch to address both.

~Andrew