Re: [PATCH] btrfs: Fix backref.c selftest compilation warning

[Tang Bin]

Hi David:

On 2020/4/14 23:22, David Sterba wrote:
> On Tue, Apr 14, 2020 at 05:19:31PM +0200, David Sterba wrote:
> > On Sat, Apr 11, 2020 at 11:49:15PM +0800, Tang Bin wrote:
> > > Fix missing braces compilation warning in the ARM
> > > compiler environment:
> > >      fs/btrfs/backref.c: In function âis_shared_data_backrefâ:
> > >      fs/btrfs/backref.c:394:9: warning: missing braces around initializer [-Wmissing-braces]
> > >        struct prelim_ref target = {0};
> > >      fs/btrfs/backref.c:394:9: warning: (near initialization for âtarget.rbnodeâ) [-Wmissing-braces]
> > >
> > > Signed-off-by: Tang Bin <tangbin@xxxxxxxxxxxxxxxxxxxx>
> > > Signed-off-by: Shengju Zhang <zhangshengju@xxxxxxxxxxxxxxxxxxxx>
> > > ---
> > >   fs/btrfs/backref.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
> > > index 9c380e7..0cc0257 100644
> > > --- a/fs/btrfs/backref.c
> > > +++ b/fs/btrfs/backref.c
> > > @@ -391,7 +391,7 @@ static int is_shared_data_backref(struct preftrees *preftrees, u64 bytenr)
> > >   	struct rb_node **p = &preftrees->direct.root.rb_root.rb_node;
> > >   	struct rb_node *parent = NULL;
> > >   	struct prelim_ref *ref = NULL;
> > > -	struct prelim_ref target = {0};
> > > +	struct prelim_ref target = {};
> > I wonder why this initialization is a problem while there are about 20
> > other uses of "{0}". The warning is about the embedded rbnode, but why
> > does a more recent compiler not warn about that? Is this a missing fix
> > from the one you use?
> >
> > I don't mind fixing compiler warnings as long as it bothers enough
> > people, eg. we have fixes reported by gcc 7 but I'm hesitant to fix
> > anything older without a good reason.
> This seems to be the bug report
>
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53119
> "Bug 53119 - -Wmissing-braces wrongly warns about universal zero
> initializer {0} "

Thank you for your reply. My tool chain is 
"arm-linux-gnueabihf-gcc(Linaro GCC 4.9-2017.01) 4.9.4".

I was trying to do an experiment on the hardware so I compiled it and 
there was a warning. Maybe as Qu Wenruo said possible tools are old?

Thank you for your patience,

Tang Bin