Re: [PATCH] checkpatch: prefer = {} initializations to = {0}
From: Christophe JAILLET <hidden>
Date: 2021-08-14 13:59:40
Also in:
lkml
Hi all, Le 05/08/2021 à 12:43, Dan Carpenter a écrit :
quoted hunk ↗ jump to hunk
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 <redacted> --- 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 (local)
[2]: Leon Romanovsky -
https://lore.kernel.org/netdev/YRFGxxkNyJDxoGWu@shredder/T/#efe1b6c7862b7ca9588c2734f04be5ef94e03d446 (local)