linux-kernel - RE: [PATCH v3 3/3] asm-generic/io.h: Silence -Wnull-pointer-arithmetic warning on PCI

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Date:   Wed, 21 Apr 2021 11:24:47 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Niklas Schnelle' <schnelle@...ux.ibm.com>,
        Arnd Bergmann <arnd@...db.de>,
        Vineet Gupta <vgupta@...opsys.com>,
        "David S. Miller" <davem@...emloft.net>
CC:     Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        "clang-built-linux@...glegroups.com" 
        <clang-built-linux@...glegroups.com>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>
Subject: RE: [PATCH v3 3/3] asm-generic/io.h: Silence
 -Wnull-pointer-arithmetic warning on PCI_IOBASE

From: Niklas Schnelle
> Sent: 21 April 2021 12:18
> 
> When PCI_IOBASE is not defined, it is set to 0 such that it is ignored
> in calls to the readX/writeX primitives. This triggers clang's
> -Wnull-pointer-arithmetic warning and will result in illegal accesses on
> platforms that do not support I/O ports if drivers do still attempt to
> access them.
> 
> Make things explicit and silence the warning by letting inb() and
> friends fail with WARN_ONCE() and a 0xff... return in case PCI_IOBASE is
> not defined.
...
> 
> diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h
> index c6af40ce03be..aabb0a8186ee 100644
> --- a/include/asm-generic/io.h
> +++ b/include/asm-generic/io.h
...
> @@ -458,12 +454,17 @@ static inline void writesq(volatile void __iomem *addr, const void *buffer,
>  #define _inb _inb
>  static inline u8 _inb(unsigned long addr)
>  {
> +#ifdef PCI_IOBASE
>  	u8 val;
> 
>  	__io_pbr();
>  	val = __raw_readb(PCI_IOBASE + addr);
>  	__io_par(val);
>  	return val;
> +#else
> +	WARN_ONCE(1, "No I/O port support\n");
> +	return ~0;
> +#endif
>  }
>  #endif

I suspect that this might be better not inlined
when PCI_IOBASE is undefined.

Otherwise you get quite a lot of bloat from all the
WARN_ONCE() calls.

	David

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