linux-kernel - Re: [PATCH] kvm: arm64: use BUG() instead of BUG

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Message-ID: <20250807155626.GA2145434@ax162>
Date: Thu, 7 Aug 2025 08:56:26 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] kvm: arm64: use BUG() instead of BUG_ON(1)

On Thu, Aug 07, 2025 at 09:21:28AM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> The BUG_ON() macro adds a little bit of complexity over BUG(), and in
> some cases this ends up confusing the compiler's control flow analysis
> in a way that results in a warning. This one now shows up with clang-21:
> 
> arch/arm64/kvm/vgic/vgic-mmio.c:1094:3: error: variable 'len' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
>  1094 |                 BUG_ON(1);
> 
> Change both instances of BUG_ON(1) to a plain BUG() in the arm64 kvm
> code, to avoid the false-positive warning.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Yeah I had responded to a build report around this but I never followed
up on seeing if it got fixed.

https://lore.kernel.org/20250714171559.GA1364710@ax162/

Reviewed-by: Nathan Chancellor <nathan@...nel.org>

> ---
>  arch/arm64/kvm/hyp/nvhe/list_debug.c | 2 +-
>  arch/arm64/kvm/vgic/vgic-mmio.c      | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/list_debug.c b/arch/arm64/kvm/hyp/nvhe/list_debug.c
> index 46a2d4f2b3c6..baa6260f88dc 100644
> --- a/arch/arm64/kvm/hyp/nvhe/list_debug.c
> +++ b/arch/arm64/kvm/hyp/nvhe/list_debug.c
> @@ -17,7 +17,7 @@ static inline __must_check bool nvhe_check_data_corruption(bool v)
>  		bool corruption = unlikely(condition);			 \
>  		if (corruption) {					 \
>  			if (IS_ENABLED(CONFIG_BUG_ON_DATA_CORRUPTION)) { \
> -				BUG_ON(1);				 \
> +				BUG();				 	 \
>  			} else						 \
>  				WARN_ON(1);				 \
>  		}							 \
> diff --git a/arch/arm64/kvm/vgic/vgic-mmio.c b/arch/arm64/kvm/vgic/vgic-mmio.c
> index e416e433baff..a573b1f0c6cb 100644
> --- a/arch/arm64/kvm/vgic/vgic-mmio.c
> +++ b/arch/arm64/kvm/vgic/vgic-mmio.c
> @@ -1091,7 +1091,7 @@ int vgic_register_dist_iodev(struct kvm *kvm, gpa_t dist_base_address,
>  		len = vgic_v3_init_dist_iodev(io_device);
>  		break;
>  	default:
> -		BUG_ON(1);
> +		BUG();
>  	}
>  
>  	io_device->base_addr = dist_base_address;
> -- 
> 2.39.5
> 
>