linux-kernel - Re: [PATCH] IB/mlx4: Avoid implicit enumerated type conversion

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Message-ID: <CAKwvOd=qNZsfSFJUFZqBbSYt4T_T7TudohzhTqpigvDAHek78A@mail.gmail.com>
Date:   Thu, 27 Sep 2018 15:42:24 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     bvanassche@....org
Cc:     jgg@...pe.ca, Nathan Chancellor <natechancellor@...il.com>,
        dledford@...hat.com, linux-rdma@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] IB/mlx4: Avoid implicit enumerated type conversion

On Thu, Sep 27, 2018 at 3:33 PM Bart Van Assche <bvanassche@....org> wrote:
>
> On Thu, 2018-09-27 at 16:28 -0600, Jason Gunthorpe wrote:
> > On Thu, Sep 27, 2018 at 01:34:16PM -0700, Nick Desaulniers wrote:
> >
> > > > Neither ib_qp_create_flags nor mlx4_ib_qp_flags have negative values, is
> > > > signedness necessary?
> > >
> > > enums are by default restricted to the range of ints.
> >
> > That's not quite right, the compiler sizes the enum to be able to fit
> > the largest value contained within, today that is int, but if we added
> > 1<<31, then it would become larger.
>
> Hi Jason,
>
> Are you perhaps confusing C and C++? For C++, an enumeration whose underlying
> type is not fixed, the underlying type is an integral type that can represent
> all the enumerator values defined in the enumeration. For C however I think
> that enumeration values are restricted to what fits in an int.
>
> Bart.
>

To quote the sacred texts (ANSIIISO9899-1990):

6.5.2.2 Enumeration specifiers
The expression that defines the value of an enumeration constant shall
be an integral constant
expression that has a value representable as an int.
-- 
Thanks,
~Nick Desaulniers