kvm: arm64: use BUG() instead of BUG_ON(1)

[PATCH] kvm: arm64: use BUG() instead of BUG_ON(1)

Posted by Arnd Bergmann 1 month, 4 weeks ago

From: Arnd Bergmann <arnd@arndb.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@arndb.de>
---
 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

Re: [PATCH] kvm: arm64: use BUG() instead of BUG_ON(1)

Posted by Oliver Upton 1 month, 3 weeks ago

On Thu, 07 Aug 2025 09:21:28 +0200, Arnd Bergmann wrote:
> 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);
> 
> [...]

Applied to fixes, thanks!

[1/1] kvm: arm64: use BUG() instead of BUG_ON(1)
      https://git.kernel.org/kvmarm/kvmarm/c/700d6868fee2

--
Best,
Oliver

Re: [PATCH] kvm: arm64: use BUG() instead of BUG_ON(1)

Posted by Nathan Chancellor 1 month, 4 weeks ago

On Thu, Aug 07, 2025 at 09:21:28AM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.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@arndb.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@kernel.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
> 
>