linux-kernel - Re: [PATCH v2] isdn: avm: Fix string plus integer warning from Clang

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Message-ID: <CAKwvOdnyhpho0x-fi03RQOrqqBFYfKdScSj9FDWPFOvg2DrGsg@mail.gmail.com>
Date:   Thu, 10 Jan 2019 10:57:44 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Karsten Keil <isdn@...ux-pingi.de>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] isdn: avm: Fix string plus integer warning from Clang

On Wed, Jan 9, 2019 at 9:42 PM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> A recent commit in Clang expanded the -Wstring-plus-int warning, showing
> some odd behavior in this file.
>
> drivers/isdn/hardware/avm/b1.c:426:30: warning: adding 'int' to a string does not append to the string [-Wstring-plus-int]
>                 cinfo->version[j] = "\0\0" + 1;
>                                     ~~~~~~~^~~
> drivers/isdn/hardware/avm/b1.c:426:30: note: use array indexing to silence this warning
>                 cinfo->version[j] = "\0\0" + 1;
>                                            ^
>                                     &      [  ]
> 1 warning generated.
>
> This is equivalent to just "\0". Nick pointed out that it is smarter to
> use "" instead of "\0" because "" is used elsewhere in the kernel and
> can be deduplicated at the linking stage.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/309
> Suggested-by: Nick Desaulniers <ndesaulniers@...gle.com>

Thanks for sending the v2.  I'll leave review to the maintainers to
confirm my suspicions about the code's intent.

> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
>
> v1 -> v2:
>
> * Use "" instead of "\0", as they are equivalent, but "" can be
>   deduplicated by the linker, as pointed out by Nick.
>
>  drivers/isdn/hardware/avm/b1.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/isdn/hardware/avm/b1.c b/drivers/isdn/hardware/avm/b1.c
> index 4ac378e48902..40ca1e8fa09f 100644
> --- a/drivers/isdn/hardware/avm/b1.c
> +++ b/drivers/isdn/hardware/avm/b1.c
> @@ -423,7 +423,7 @@ void b1_parse_version(avmctrl_info *cinfo)
>         int i, j;
>
>         for (j = 0; j < AVM_MAXVERSION; j++)
> -               cinfo->version[j] = "\0\0" + 1;
> +               cinfo->version[j] = "";
>         for (i = 0, j = 0;
>              j < AVM_MAXVERSION && i < cinfo->versionlen;
>              j++, i += cinfo->versionbuf[i] + 1)
> --
> 2.20.1
>


-- 
Thanks,
~Nick Desaulniers