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

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Message-ID: <CAKwvOdmaZ6bbnkPGqEeaB6MMnLm+7Q14MUbbq_kNz5usgcU0bA@mail.gmail.com>
Date:   Tue, 8 Jan 2019 09:50:39 -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] isdn: avm: Fix string plus integer warning from Clang

On Mon, Jan 7, 2019 at 9:07 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" so fix it to clean up the warning.

Hard to tell what the intent of this was.  I also assume that they
meant to set all version strings to the empty string.  I think just `=
""` would be better, as otherwise that creates a new data section
containing two zero bytes vs the empty string which already probably
exists throughout the kernel and can be deduplicated by the linker.
https://godbolt.org/z/qf3Rn8
Sorry I gave the quick LGTM in
https://github.com/ClangBuiltLinux/linux/issues/309#issuecomment-452106468,
that was my mistake.  Assuming there's no other comments (maybe from
the maintainers) on what the intent of this code actually is, would
you mind sending a V2?  (Sorry again for the quick LGTM on this
version).

>
> Link: https://github.com/ClangBuiltLinux/linux/issues/309
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
>  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..7fa8141e2019 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] = "\0";
>         for (i = 0, j = 0;
>              j < AVM_MAXVERSION && i < cinfo->versionlen;
>              j++, i += cinfo->versionbuf[i] + 1)
> --
> 2.20.1
>


-- 
Thanks,
~Nick Desaulniers