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

From: Nick Desaulniers
Date: Tue Jan 08 2019 - 12:50:53 EST


On Mon, Jan 7, 2019 at 9:07 PM Nathan Chancellor
<natechancellor@xxxxxxxxx> 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@xxxxxxxxx>
> ---
> 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