Re: [PATCH] checkpatch: prefer = {} initializations to = {0}

[Marion & Christophe JAILLET]

Copy paste error, see below :/

Le 14/08/2021 à 15:59, Christophe JAILLET a écrit :
> Hi all,
>
> Le 05/08/2021 à 12:43, Dan Carpenter a écrit :
> > The "= {};" style empty struct initializer is preferred over = {0}.
> > It avoids the situation where the first struct member is a pointer and
> > that generates a Sparse warning about assigning using zero instead of
> > NULL.  Also it's just nicer to look at.
> >
> > Some people complain that {} is less portable but the kernel has
> > different portability requirements from userspace so this is not a
> > issue that we care about.
> >
> > Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> > ---
> >   scripts/checkpatch.pl | 6 ++++++
> >   1 file changed, 6 insertions(+)
> >
> > diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> > index 461d4221e4a4..32c8a0ca6fd0 100755
> > --- a/scripts/checkpatch.pl
> > +++ b/scripts/checkpatch.pl
> > @@ -4029,6 +4029,12 @@ sub process {
> >                    "Using $1 is unnecessary\n" . $herecurr);
> >           }
> > +# prefer = {}; to = {0};
> > +        if ($line =~ /= \{ *0 *\}/) {
> > +            WARN("ZERO_INITIALIZER",
> > +                 "= {} is preferred over = {0}\n" . $herecurr);
> > +        }
> > +
> >   # Check for potential 'bare' types
> >           my ($stat, $cond, $line_nr_next, $remain_next, $off_next,
> >               $realline_next);
>
> [1] and [2] state that {} and {0} don't have the same effect. So if 
> correct, this is not only a matter of style.
>
> When testing with gcc 10.3.0, I arrived at the conclusion that both {} 
> and {0} HAVE the same behavior (i.e the whole structure and included 
> structures are completely zeroed) and I don't have a C standard to check 
> what the rules are.
> gcc online doc didn't help me either.
>
> To test, I wrote a trivial C program, compiled it with gcc -S and looked 
> at the assembly files.
>
>
> Maybe, if it is an undefined behavior, other compilers behave 
> differently than gcc.
>
>
> However, the 2 persons listed bellow have a much better Linux and C 
> background than me. So it is likely that my testings were too naive.
>
>
> Can someone provide some rational or compiler output that confirms that 
> {} and {0} are not the same?
>
> Because if confirmed, I guess that there is some clean-up work to do all 
> over the code, not only to please Sparse!
>
>
> Thanks in advance.
> CJ
>
>
>
> [1]: Russell King - 
> https://lore.kernel.org/netdev/YRFGxxkNyJDxoGWu@shredder/T/#efe1b6c7862b7ca9588c2734f04be5ef94e03d446 
>
>
> [2]: Leon Romanovsky - 
> https://lore.kernel.org/netdev/YRFGxxkNyJDxoGWu@shredder/T/#efe1b6c7862b7ca9588c2734f04be5ef94e03d446 
https://lore.kernel.org/netdev/162894660670.3097.4150652110351873021.git-patchwork-notify@xxxxxxxxxx/T/#m3424d6e97ef0f0ddd429cce3369a6da0ea9af276