Re: [PATCH v2 1/2] qom/object: add available_if field to TypeInfo

[Markus Armbruster <armbru@redhat.com>]

Pierrick Bouvier <pierrick.bouvier@oss.qualcomm.com> writes:

> With the single-binary, we start mixing types for different targets,
> that may or may not be available for current one.
>
> Previously, we implemented an approach based on interfaces, but it
> proved to be too limited. It requires duplication between
> machines/cpus/devices, and does not handle specific cases where a type
> should be available based on a target configuration (Kconfig).
>
> To solve this, we add a new field, available_if, to TypeInfo.
> It is an array containing a list of requirements for type to be
> available.
>
> For now, we have only targets as requirements, but later we'll add
> specific target config entries also.
>
> We also add a TARGET_REQS macro, to declare a list of requirements. For
> sanity sake, we don't use a complex variadic macro prefixing each
> parameter. It requires a lot of macro boilerplate in C, and prevent
> readers to jump easily to definition for each parameter.
>
> Signed-off-by: Pierrick Bouvier <pierrick.bouvier@oss.qualcomm.com>
> ---
>  include/qemu/target-info.h | 11 +++++++++++
>  include/qom/object.h       |  5 +++++
>  qom/object.c               | 10 ++++++++++
>  rust/qom/src/qom.rs        |  1 +
>  stubs/meson.build          |  1 +
>  stubs/target-info.c        | 11 +++++++++++
>  target-info.c              | 13 +++++++++++++
>  7 files changed, 52 insertions(+)
>  create mode 100644 stubs/target-info.c
>
> diff --git a/include/qemu/target-info.h b/include/qemu/target-info.h
> index 6c5b714288e..6379e65bbcf 100644
> --- a/include/qemu/target-info.h
> +++ b/include/qemu/target-info.h
> @@ -50,6 +50,17 @@ const char *target_cpu_type(void);
>   */
>  bool target_big_endian(void);
>  
> +typedef enum TargetReq {
> +    /* 0 is reserved for end of array */
> +    TARGET_REQ_BASE_ARM = 1,
> +    TARGET_REQ_AARCH64,
> +    TARGET_REQ_ARM,
> +} TargetReq;
> +
> +#define TARGET_REQS(...) (const TargetReq[]){__VA_ARGS__, 0}

The sentinel 0 is not a member of the enum.

Is this safe?  I'm asking because the C standard is infatuated with
undefined behavior.  Checking C99...  all I can find is Annex I "Common
warnings"

         -- A  value  is  given to an object of an enumeration type
            other than by assignment  of  an  enumeration  constant
            that  is  a  member  of  that  type,  or an enumeration
            variable that has the same type,  or  the  value  of  a
            function   that   returns  the  same  enumeration  type

Looks like it's safe.

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