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

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Date:   Tue, 8 Jan 2019 10:54:14 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.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 Tue, Jan 08, 2019 at 09:50:39AM -0800, Nick Desaulniers wrote:
> 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).

Of course, thank you for the explanation and further exploration. I'll
send a v2 later today/tomorrow to give some time for the maintainers to
chime in.

> 
> >
> > 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