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

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Message-ID: <d3bd266c-922f-d1b6-5b14-edd892ad7fd1@redhat.com>
Date: Mon, 15 Jul 2024 12:43:58 +0200 (CEST)
From: Sebastian Ott <sebott@...hat.com>
To: Mark Rutland <mark.rutland@....com>
cc: Marc Zyngier <maz@...nel.org>, linux-arm-kernel@...ts.infradead.org, 
    kvmarm@...ts.linux.dev, linux-kernel@...r.kernel.org, 
    Oliver Upton <oliver.upton@...ux.dev>, James Morse <james.morse@....com>, 
    Suzuki K Poulose <suzuki.poulose@....com>, 
    Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
    Zenghui Yu <yuzenghui@...wei.com>
Subject: Re: [PATCH 1/3] KVM: arm64: fix override-init warnings in W=1
 builds

On Mon, 15 Jul 2024, Mark Rutland wrote:
> On Fri, Jul 12, 2024 at 10:55:16PM +0100, Marc Zyngier wrote:
>> On Fri, 12 Jul 2024 12:03:30 +0100,
>> Sebastian Ott <sebott@...hat.com> 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@...hat.com>
>>> ---
>>>  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.
>
> IMO this would be a lot more palatable if this were an attribute on the
> struct or assignment, like we asked for in the past:
>
>  https://lore.kernel.org/lkml/20190809083251.GA48423@lakrids.cambridge.arm.com/
>
> Having something that we could put specifically on the default assignment would
> make this a lot more legible and better capture the intent.

Yea, I double checked in the gcc doc - there seems to be no other means to
silence this per var or assignment. We can disable that in the makefile
for the whole file or dir or we keep it as it is.

Thanks,
Sebastian