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

Christophe JAILLET
2021-08-14T13:59:35Z

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@oracle.com>
> ---
> 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 -