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

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Message-ID: <CAK8P3a0u5w1C+L6t9h5+4fu0gt79u68B+txhF6adAT3MVfwW3Q@mail.gmail.com>
Date:   Tue, 5 Sep 2017 09:28:25 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Martin Wilck <mwilck@...e.com>
Cc:     Christoph Hellwig <hch@....de>,
        Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Martin Wilck <mwilck@...e.de>,
        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 Mon, Aug 14, 2017 at 10:12 PM, Martin Wilck <mwilck@...e.com> wrote:
> This helper function is useful for the nvme subsystem, and maybe
> others.
>
> Note: the warnings reported by the kbuild test robot for this patch
> are actually generated by the use of CONFIG_PROFILE_ALL_BRANCHES
> together with __FORTIFY_INLINE.
>
> Signed-off-by: Martin Wilck <mwilck@...e.com>
> ---

>  #if !defined(__NO_FORTIFY) && defined(__OPTIMIZE__) && defined(CONFIG_FORTIFY_SOURCE)
> @@ -395,4 +396,33 @@ __FORTIFY_INLINE char *strcpy(char *p, const char *q)
>
>  #endif
>
> +/**
> + * 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.

       Arnd