linux-kernel - Re: [PATCH] kbuild: Disable -Wpointer-to-enum-cast

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Date:   Tue, 10 Mar 2020 09:48:40 -0700
From:   Joe Perches <joe@...ches.com>
To:     Masahiro Yamada <masahiroy@...nel.org>,
        David Laight <David.Laight@...lab.com>
Cc:     Nathan Chancellor <natechancellor@...il.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH] kbuild: Disable -Wpointer-to-enum-cast

On Wed, 2020-03-11 at 00:30 +0900, Masahiro Yamada wrote:
> On Tue, Mar 10, 2020 at 8:31 PM David Laight <David.Laight@...lab.com> wrote:
> > From: Nathan Chancellor
> > > Sent: 10 March 2020 01:26
> > ...
> > > Sure, I can send v2 to do that but I think that sending 97 patches just
> > > casting the small values (usually less than twenty) to unsigned long
> > > then to the enum is rather frivolous. I audited at least ten to fifteen
> > > of these call sites when creating the clang patch and they are all
> > > basically false positives.
> > 
> > Such casts just make the code hard to read.
> > If misused casts can hide horrid bugs.
> > IMHO sprinkling the code with casts just to remove
> > compiler warnings will bite back one day.
> > 
> 
> I agree that too much casts make the code hard to read,
> but irrespective of this patch, there is no difference
> in the fact that we need a cast to convert
> (const void *) to a non-pointer value.
> 
> The difference is whether we use
> (uintptr_t) or (enum foo).

or hide it altogether in a macro like cast_to

#define cast_to(type, val)	\
	etc...

where cast_to could do the appropriate
intermediate cast if type is an enum
and sizeof(tupeof val) is larger than int