linux-kernel - Re: [RFC PATCH 03/13] usb: remove the usage of the list iterator after the loop

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Date:   Wed, 23 Feb 2022 12:43:10 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Jakob <jakobkoschel@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Mike Rapoport <rppt@...nel.org>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Brian Johannesmeyer <bjohannesmeyer@...il.com>,
        Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>
Subject: Re: [RFC PATCH 03/13] usb: remove the usage of the list iterator
 after the loop

On Wed, Feb 23, 2022 at 12:25 PM Arnd Bergmann <arnd@...db.de> wrote:
>
> I looked at the gcc documentation for this flag, and it tells me that
> it's default-enabled for std=c99 or higher. Turning it on for --std=gnu89
> shows the same warning, so at least it doesn't sound like the actual
> behavior changed, only the warning output. clang does not warn
> for this code at all, regardless of the --std= flag.

Ok, so we should be able to basically convert '--std=gnu89' into
'--std=gnu11 -Wno-shift-negative-value' with no expected change of
behavior.

Of course, maybe we need to make -Wno-shift-negative-value be
conditional on the compiler supporting it in the first place?

I really would love to finally move forward on this, considering that
it's been brewing for many many years.

I think the loop iterators are the biggest user-visible thing, but
there might be others.

And some googling seems to show that the reason for
-Wshift-negative-value is that with C99 the semantics changed for
targets that weren't two's complement. We *really* don't care.

Of course, the C standard being the bunch of incompetents they are,
they in the process apparently made left-shifts undefined (rather than
implementation-defined). Christ, they keep on making the same mistakes
over and over. What was the definition of insanity again?

                  Linus