Re: [Qemu-devel] [PATCH v3 15/49] qapi: do not define enumeration value explicitely

[Markus Armbruster]

Subject: explicitly

Marc-André Lureau <address@hidden> writes:

> The C standard has the initial value at 0 and the subsequent values
> incremented by 1. No need to set this explicitely.
>
> This will prevent from artificial "gaps" when compiling out some enum
> values and having unnecessarily large MAX values & enums arrays.
>
> Signed-off-by: Marc-André Lureau <address@hidden>
> ---
>  scripts/qapi/common.py | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/scripts/qapi/common.py b/scripts/qapi/common.py
> index 60c1d0a783..68a567f53f 100644
> --- a/scripts/qapi/common.py
> +++ b/scripts/qapi/common.py
> @@ -2032,14 +2032,11 @@ typedef enum %(c_name)s {
>  ''',
>                  c_name=c_name(name))
>  
> -    i = 0
>      for value in enum_values:
>          ret += mcgen('''
> -    %(c_enum)s = %(i)d,
> +    %(c_enum)s,
>  ''',
> -                     c_enum=c_enum_const(name, value, prefix),
> -                     i=i)
> -        i += 1
> +                     c_enum=c_enum_const(name, value, prefix))
>  
>      ret += mcgen('''
>  } %(c_name)s;

What excactly in your series depends on this?

What safeguards do you propose to ensure an enumeration with
conditionals is compiled only with the exact same conditionals within
the same program?

Example of the kind of deathtrap to guard against: compile

    typedef enum Color {
        COLOR_WHITE,
#if defined(NEED_CPU_H)
#if defined(TARGET_S390X)
        COLOR_BLUE,
#endif /* defined(TARGET_S390X) */
#endif /* defined(NEED_CPU_H) */
        COLOR_BLACK,
    } Color;

in s390x-code (COLOR_BLACK = 2) and in target-independent code
(COLOR_BLACK = 1), then linking the two together.

Yes, I know a similar deathtrap will be set up for struct and union
types.  No excuse for ignoring either of the two.