Re: [PATCH 1/3] KVM: arm64: fix override-init warnings in W=1 builds

[Sebastian Ott]

On Fri, 12 Jul 2024, Marc Zyngier wrote:
> On Fri, 12 Jul 2024 12:03:30 +0100,
> Sebastian Ott <sebott@xxxxxxxxxx> wrote:
> > Remove double initializations in cases where that's easily possible
> > - like extra NULL initialization in static global structures. In the
> > other cases just silence -Woverride-init.
> >
> > To fix warnings like the following:
> > arch/arm64/kvm/hyp/vhe/switch.c:271:43: warning: initialized field overwritten [-Woverride-init]
> >   271 |         [ESR_ELx_EC_CP15_32]            = kvm_hyp_handle_cp15_32,
> >       |                                           ^~~~~~~~~~~~~~~~~~~~~~
> >
> > Signed-off-by: Sebastian Ott <sebott@xxxxxxxxxx>
> > ---
> >  arch/arm64/kvm/handle_exit.c     | 5 +++++
> >  arch/arm64/kvm/hyp/nvhe/switch.c | 6 ++----
> >  arch/arm64/kvm/hyp/vhe/switch.c  | 3 +--
> >  arch/arm64/kvm/sys_regs.c        | 5 +++++
> >  4 files changed, 13 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> > index d7c2990e7c9e..2c049746657c 100644
> > --- a/arch/arm64/kvm/handle_exit.c
> > +++ b/arch/arm64/kvm/handle_exit.c
> > @@ -291,6 +291,9 @@ static int handle_svc(struct kvm_vcpu *vcpu)
> >  	return 1;
> >  }
> >
> > +__diag_push();
> > +__diag_ignore_all("-Woverride-init", "Allow field overrides in exit_handlers");
>
> The wording you are looking for is "Silence stupid warning". I really
> mean it. There is really nothing wrong with this code, and if the
> compiler doesn't understand the purpose of a default initialiser, then
> *maybe* it should be fixed rather than polluting the kernel with this
> stuff.
[...]
> > -static const exit_handler_fn hyp_exit_handlers[] = {
> > -	[0 ... ESR_ELx_EC_MAX]		= NULL,
> > +static const exit_handler_fn hyp_exit_handlers[ESR_ELx_EC_MAX + 1] = {
>
> Is this really any better? I don't think so. It makes the intent
> disappear instead of making it explicit. Intent matters *a lot*.

I'm not claiming that it's an improvement to the code. But yea, I see your
point. How about disabling that flag in the makefile?

Thanks,
Sebastian