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 :

quoted

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) 

https://lore.kernel.org/netdev/162894660670.3097.4150652110351873021.git-patchwork-notify@kernel.org/T/#m3424d6e97ef0f0ddd429cce3369a6da0ea9af276 (local)