linux-kernel - Re: [PATCH v4 2/3] string.h: add memcpy_and

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Message-ID: <1504635482.4516.3.camel@suse.com>
Date:   Tue, 05 Sep 2017 20:18:02 +0200
From:   Martin Wilck <mwilck@...e.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Christoph Hellwig <hch@....de>,
        Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Hannes Reinecke <hare@...e.de>, linux-nvme@...ts.infradead.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 2/3] string.h: add memcpy_and_pad()

On Tue, 2017-09-05 at 09:28 +0200, Arnd Bergmann wrote:
> 
> > +/**
> > + * memcpy_and_pad - Copy one buffer to another with padding
> > + * @dest: Where to copy to
> > + * @dest_len: The destination buffer size
> > + * @src: Where to copy from
> > + * @count: The number of bytes to copy
> > + * @pad: Character to use for padding if space is left in
> > destination.
> > + */
> > +__FORTIFY_INLINE void memcpy_and_pad(void *dest, size_t dest_len,
> > +                                    const void *src, size_t count,
> > int pad)
> > +{
> 
> This is causing compile-time warnings for me:
> 
> In file included from /git/arm-soc/arch/x86/include/asm/string.h:2:0,
>                  from /git/arm-soc/include/linux/string.h:18,
>                  from /git/arm-soc/arch/x86/include/asm/page_32.h:34,
>                  from /git/arm-soc/arch/x86/include/asm/page.h:13,
>                  from /git/arm-
> soc/arch/x86/include/asm/thread_info.h:11,
>                  from /git/arm-soc/include/linux/thread_info.h:37,
>                  from /git/arm-soc/arch/x86/include/asm/preempt.h:6,
>                  from /git/arm-soc/include/linux/preempt.h:80,
>                  from /git/arm-soc/include/linux/spinlock.h:50,
>                  from /git/arm-soc/include/linux/seqlock.h:35,
>                  from /git/arm-soc/include/linux/time.h:5,
>                  from /git/arm-soc/include/linux/stat.h:18,
>                  from /git/arm-soc/include/linux/module.h:10,
>                  from /git/arm-soc/drivers/md/dm-integrity.c:9:
> /git/arm-soc/arch/x86/include/asm/string_32.h:196:25: error:
> '__memcpy' is static but used in inline function 'memcpy_and_pad'
> which is not static [-Werror]
>  #define memcpy(t, f, n) __memcpy((t), (f), (n))
>                          ^~~~~~~~
> /git/arm-soc/include/linux/string.h:466:3: note: in expansion of
> macro 'memcpy'
> 
>    ^
> /git/arm-soc/arch/x86/include/asm/string_32.h:196:25: error:
> '__memcpy' is static but used in inline function 'memcpy_and_pad'
> which is not static [-Werror]
>  #define memcpy(t, f, n) __memcpy((t), (f), (n))
>                          ^~~~~~~~
> 
> The problem is the use of __FORTIFY_INLINE outside of the #ifdef
> section above it.
> I used an ugly local workaround, duplicating the function with a
> 'static inline' variant
> in an #else block. Alternatively we could add an extern version in
> lib/string.c for the
> non-fortified case.

I'm sorry. It seems that I messed the code up by trying to do it right.
I suggest to simply drop the fortification code from this function,
which is not a "common str/mem function" anyway. Please tell me if
that'd be ok for you.

I'll send a patch in a follow-up email. 

Martin

-- 
Dr. Martin Wilck <mwilck@...e.com>, Tel. +49 (0)911 74053 2107
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)