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

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Message-ID: <6729109ae6ad429f87270e2bef2eed2f@AcuMS.aculab.com>
Date:   Mon, 28 Feb 2022 06:15:59 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Linus Torvalds' <torvalds@...ux-foundation.org>,
        Segher Boessenkool <segher@...nel.crashing.org>
CC:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Arnd Bergmann <arnd@...db.de>, 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: Linus Torvalds
> Sent: 27 February 2022 21:05
...
> And then the C standards people decided that "because our job isn't to
> describe all the architectural issues you can hit, we'll call it
> undefined, and in the process let compiler people intentionally break
> it".
> 
> THAT is a problem.

I'm waiting for them to decide that memset(ptr, 0, len) of
any structure that contains a pointer is UB (because a NULL
pointer need not be the all zero bit pattern) so decide
to discard the call completely (or some such).

Non-zero NULL pointers is the only reason arithmetic on NULL
pointers isn't valid.

Or maybe that character range tests are UB because '0' to '9'
don't have to be adjacent - they are even adjacent in EBCDIC.

Some of the 'strict aliasing' bits are actually useful since
they let the compiler reorder reads and writes.
But the definition is brain-dead.
Sometimes it would be nice to have byte writes reordered,
but even using int:8 doesn't work.

I have never worked out what 'restrict' actually does,
in any places I've tried it did nothing.
Although I may have been hoping it would still help when
the function got inlined.

	David

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