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

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Message-Id: <20190119.100200.853063369704641480.davem@davemloft.net>
Date:   Sat, 19 Jan 2019 10:02:00 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     natechancellor@...il.com
Cc:     isdn@...ux-pingi.de, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, ndesaulniers@...gle.com
Subject: Re: [PATCH v2] isdn: avm: Fix string plus integer warning from
 Clang

From: Nathan Chancellor <natechancellor@...il.com>
Date: Wed,  9 Jan 2019 22:41:08 -0700

> 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>
> 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.

Applied, that was certainly a funny construct....

It obviously is trying to initialize the array elements to pointers
to empty strings.