Re: [PATCH] perf build: Restore {0} initializer since GCC-15

[James Clark]

On 19/03/2025 11:19 am, James Clark wrote:
> On 19/03/2025 11:04 am, Leo Yan wrote:
> > GCC-15 release claims [1]:
> >
> >   {0} initializer in C or C++ for unions no longer guarantees clearing
> >   of the whole union (except for static storage duration initialization),
> >   it just initializes the first union member to zero. If initialization
> >   of the whole union including padding bits is desirable, use {} (valid
> >   in C23 or C++) or use -fzero-init-padding-bits=unions option to
> >   restore old GCC behavior.
> >
> > This new behaviour might cause stale and unexpected data we defined in
> > Perf.  Add the -fzero-init-padding-bits=unions option for entirely
> > zeroing union structures.
>
> Do we need this? I don't see any unions initialized in that way. In fact 
> there is only one struct initialized with {0}, the other handful are 
> char*s but I don't think either are affected.
>
> Adding options that allow people to add more non standard code doesn't 
> feel very portable or in the spirit of doing it the right way. Maybe 
> there's an argument that it guards against future mistakes, but it's not 
> mentioned in the commit message.


After reading in a bit more detail and seeing all the extra 
inconsistencies between compilers/versions/syntaxes etc I retract this 
and agree that -fzero-init-padding-bits=all would be harmless and only 
make things better.