linux-kernel - Re: powerpc: io-defs.h:43:1: error: performing pointer arithmetic on a null pointer has undefined behavior [-Werror,-Wnull-pointer-arithmetic]

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Date: Tue, 16 Apr 2024 05:38:19 -0500
From: Segher Boessenkool <segher@...nel.crashing.org>
To: Naresh Kamboju <naresh.kamboju@...aro.org>
Cc: open list <linux-kernel@...r.kernel.org>, lkft-triage@...ts.linaro.org,
        Linux Regressions <regressions@...ts.linux.dev>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
        Anders Roxell <anders.roxell@...aro.org>,
        Kees Cook <keescook@...omium.org>, Arnd Bergmann <arnd@...db.de>,
        clang-built-linux <llvm@...ts.linux.dev>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>, Jeff Xu <jeffxu@...omium.org>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Dan Carpenter <dan.carpenter@...aro.org>
Subject: Re: powerpc: io-defs.h:43:1: error: performing pointer arithmetic on a null pointer has undefined behavior [-Werror,-Wnull-pointer-arithmetic]

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 :-(


Segher