linux-kernel - RE: [PATCH] asm-generic/io.h: Silence -Wnull-pointer-arithmetic warning on PCI

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Date:   Tue, 13 Apr 2021 12:56:44 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Arnd Bergmann' <arnd@...db.de>,
        Niklas Schnelle <schnelle@...ux.ibm.com>
CC:     Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>
Subject: RE: [PATCH] asm-generic/io.h: Silence -Wnull-pointer-arithmetic
 warning on PCI_IOBASE

From: Arnd Bergmann
> Sent: 13 April 2021 13:27
> 
> On Tue, Apr 13, 2021 at 1:54 PM Niklas Schnelle <schnelle@...ux.ibm.com> wrote:
> >
> > When PCI_IOBASE is not defined, it is set to 0 such that it is ignored
> > in calls to the readX/writeX primitives. While mathematically obvious
> > this triggers clang's -Wnull-pointer-arithmetic warning.
> 
> Indeed, this is an annoying warning.
> 
> > An additional complication is that PCI_IOBASE is explicitly typed as
> > "void __iomem *" which causes the type conversion that converts the
> > "unsigned long" port/addr parameters to the appropriate pointer type.
> > As non pointer types are used by drivers at the callsite since these are
> > dealing with I/O port numbers, changing the parameter type would cause
> > further warnings in drivers. Instead use "uintptr_t" for PCI_IOBASE
> > 0 and explicitly cast to "void __iomem *" when calling readX/writeX.

Since the definitions make no sense when PCI_IOBASE in undefined
maybe the functions should either not be defined, be stubs that
do nothing or stubs that are BUG().

	David

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