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

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Message-ID: <7abf3406919b4f0c828dacea6ce97ce8@AcuMS.aculab.com>
Date:   Sun, 27 Feb 2022 07:10:45 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Segher Boessenkool' <segher@...nel.crashing.org>,
        Arnd Bergmann <arnd@...db.de>
CC:     Linus Torvalds <torvalds@...ux-foundation.org>,
        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

From: Segher Boessenkool
> Sent: 27 February 2022 01:10
> 
> On Sat, Feb 26, 2022 at 11:14:15PM +0100, Arnd Bergmann wrote:
> > On Sat, Feb 26, 2022 at 1:42 PM Segher Boessenkool
> > <segher@...nel.crashing.org> wrote:
> > > On Wed, Feb 23, 2022 at 11:23:39AM -0800, Linus Torvalds wrote:
> >
> > >
> > > The only reason the warning exists is because it is undefined behaviour
> > > (not implementation-defined or anything).  The reason it is that in the
> > > standard is that it is hard to implement and even describe for machines
> > > that are not two's complement.  However relevant that is today :-)

I thought only right shifts of negative values were 'undefined'.
And that was to allow cpu that only had logical shift right
(ie ones that didn't propagate the sign) to be conformant.
I wonder when the last cpu like that was?

Quite why the standards keeps using the term 'undefined behaviour'
beats me - there ought to be something for 'undefined value'.

	David

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