[PATCH] linux: Fix integer overflow warnings when including <sys/mount.h> [BZ #32708]

[Collin Funk]

Florian Weimer <fweimer@redhat.com> writes:

> I believe unsigned enum types are still a GNU extension, but maybe
> <sys/mount.h> isn't expected to be processed with compilers without such
> extensions.

I don't think that unsigned enums are a GNU extension. In C99 section
6.7.2.2 [1]:

    Each enumerated type shall be compatible with char, a signed integer
    type, or an unsigned integer type. The choice of type is
    implementation-defined, 110) but shall be capable of representing the
    values of all the members of the enumeration. The enumerated type is
    incomplete until after the } that terminates the list of enumerator
    declarations.

And subscript 110:

    An implementation may delay the choice of which integer type until
    all enumeration constants have been seen.

This definition taken from Gnulib is a good demonstration of this:

    typedef enum
    {
      _Bool_must_promote_to_int = -1,
      false = 0,
      true = 1
    } _Bool;

Without _Bool_must_promote_to_int the compiler is free to chose
'unsigned int' as the type for the enum, which is unwanted in this case.

Collin

[1] https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf