From: David Laight <David.Laight@ACULAB.COM>
To: 'Segher Boessenkool' <segher@kernel.crashing.org>,
Naresh Kamboju <naresh.kamboju@linaro.org>
Cc: Nathan Chancellor <nathan@kernel.org>,
Anders Roxell <anders.roxell@linaro.org>,
Linux Regressions <regressions@lists.linux.dev>,
Arnd Bergmann <arnd@arndb.de>,
clang-built-linux <llvm@lists.linux.dev>,
"Nick Desaulniers" <ndesaulniers@google.com>,
open list <linux-kernel@vger.kernel.org>,
"lkft-triage@lists.linaro.org" <lkft-triage@lists.linaro.org>,
Aneesh Kumar K.V <aneesh.kumar@kernel.org>,
Jeff Xu <jeffxu@chromium.org>,
"Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Dan Carpenter <dan.carpenter@linaro.org>,
Kees Cook <keescook@chromium.org>
Subject: RE: powerpc: io-defs.h:43:1: error: performing pointer arithmetic on a null pointer has undefined behavior [-Werror,-Wnull-pointer-arithmetic]
Date: Tue, 16 Apr 2024 11:09:26 +0000 [thread overview]
Message-ID: <1d0de2bee67643bfa5a561e70133db75@AcuMS.aculab.com> (raw)
In-Reply-To: <20240416103819.GQ19790@gate.crashing.org>
From: Segher Boessenkool
> Sent: 16 April 2024 11:38
>
> On Tue, Apr 16, 2024 at 03:02:52PM +0530, Naresh Kamboju wrote:
> > In file included from arch/powerpc/include/asm/io.h:672:
> > arch/powerpc/include/asm/io-defs.h:43:1: error: performing pointer
> > arithmetic on a null pointer has undefined behavior
> > [-Werror,-Wnull-pointer-arithmetic]
>
> It is not UB, but just undefined: the program is meaningless.
>
> It is not a null pointer but even a null pointer constant here. It
> matters in places, including here.
>
> It would help if the warnings were more correct :-(
Isn't it only a problem because the NULL pointer isn't required to
be the all-zero bit pattern?
So when do we get a warning from using memset() on a structure
that contains pointers? Since it is equally buggy.
Has anyone ever seen a system where NULL wasn't 'all zeros'?
I've used a system where the 'native' invalid pointer was 'all ones',
but even there the C code used 'all zeros'.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
WARNING: multiple messages have this Message-ID (diff)
From: David Laight <David.Laight@ACULAB.COM>
To: 'Segher Boessenkool' <segher@kernel.crashing.org>,
Naresh Kamboju <naresh.kamboju@linaro.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@kernel.org>,
Anders Roxell <anders.roxell@linaro.org>,
Linux Regressions <regressions@lists.linux.dev>,
Arnd Bergmann <arnd@arndb.de>,
clang-built-linux <llvm@lists.linux.dev>,
Nick Desaulniers <ndesaulniers@google.com>,
open list <linux-kernel@vger.kernel.org>,
"lkft-triage@lists.linaro.org" <lkft-triage@lists.linaro.org>,
Nathan Chancellor <nathan@kernel.org>,
Jeff Xu <jeffxu@chromium.org>,
"Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Dan Carpenter <dan.carpenter@linaro.org>,
Kees Cook <keescook@chromium.org>
Subject: RE: powerpc: io-defs.h:43:1: error: performing pointer arithmetic on a null pointer has undefined behavior [-Werror,-Wnull-pointer-arithmetic]
Date: Tue, 16 Apr 2024 11:09:26 +0000 [thread overview]
Message-ID: <1d0de2bee67643bfa5a561e70133db75@AcuMS.aculab.com> (raw)
In-Reply-To: <20240416103819.GQ19790@gate.crashing.org>
From: Segher Boessenkool
> Sent: 16 April 2024 11:38
>
> On Tue, Apr 16, 2024 at 03:02:52PM +0530, Naresh Kamboju wrote:
> > In file included from arch/powerpc/include/asm/io.h:672:
> > arch/powerpc/include/asm/io-defs.h:43:1: error: performing pointer
> > arithmetic on a null pointer has undefined behavior
> > [-Werror,-Wnull-pointer-arithmetic]
>
> It is not UB, but just undefined: the program is meaningless.
>
> It is not a null pointer but even a null pointer constant here. It
> matters in places, including here.
>
> It would help if the warnings were more correct :-(
Isn't it only a problem because the NULL pointer isn't required to
be the all-zero bit pattern?
So when do we get a warning from using memset() on a structure
that contains pointers? Since it is equally buggy.
Has anyone ever seen a system where NULL wasn't 'all zeros'?
I've used a system where the 'native' invalid pointer was 'all ones',
but even there the C code used 'all zeros'.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2024-04-16 11:10 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-16 9:32 powerpc: io-defs.h:43:1: error: performing pointer arithmetic on a null pointer has undefined behavior [-Werror,-Wnull-pointer-arithmetic] Naresh Kamboju
2024-04-16 9:32 ` Naresh Kamboju
2024-04-16 10:38 ` Segher Boessenkool
2024-04-16 10:38 ` Segher Boessenkool
2024-04-16 11:09 ` David Laight [this message]
2024-04-16 11:09 ` David Laight
2024-04-16 11:01 ` Arnd Bergmann
2024-04-16 11:01 ` Arnd Bergmann
2024-04-16 11:55 ` Arnd Bergmann
2024-04-16 11:55 ` Arnd Bergmann
2024-04-16 12:42 ` Dan Carpenter
2024-04-16 12:42 ` Dan Carpenter
2024-04-16 12:44 ` Arnd Bergmann
2024-04-16 12:44 ` Arnd Bergmann
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1d0de2bee67643bfa5a561e70133db75@AcuMS.aculab.com \
--to=david.laight@aculab.com \
--cc=anders.roxell@linaro.org \
--cc=aneesh.kumar@kernel.org \
--cc=arnd@arndb.de \
--cc=dan.carpenter@linaro.org \
--cc=jeffxu@chromium.org \
--cc=keescook@chromium.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=lkft-triage@lists.linaro.org \
--cc=llvm@lists.linux.dev \
--cc=naresh.kamboju@linaro.org \
--cc=nathan@kernel.org \
--cc=naveen.n.rao@linux.ibm.com \
--cc=ndesaulniers@google.com \
--cc=regressions@lists.linux.dev \
--cc=segher@kernel.crashing.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.