Re: [PATCH] vmw_vsock: bypass false-positive Wnonnull warning with gcc-16

[Bobby Eshleman]

On Tue, Feb 03, 2026 at 05:34:00PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
> 
> The gcc-16.0.1 snapshot produces a false-positive warning that turns
> into a build failure with CONFIG_WERROR:
> 
> In file included from arch/x86/include/asm/string.h:6,
>                  from net/vmw_vsock/vmci_transport.c:10:
> In function 'vmci_transport_packet_init',
>     inlined from '__vmci_transport_send_control_pkt.constprop' at net/vmw_vsock/vmci_transport.c:198:2:
> arch/x86/include/asm/string_32.h:150:25: error: argument 2 null where non-null expected because argument 3 is nonzero [-Werror=nonnull]
>   150 | #define memcpy(t, f, n) __builtin_memcpy(t, f, n)
>       |                         ^~~~~~~~~~~~~~~~~~~~~~~~~
> net/vmw_vsock/vmci_transport.c:164:17: note: in expansion of macro 'memcpy'
>   164 |                 memcpy(&pkt->u.wait, wait, sizeof(pkt->u.wait));
>       |                 ^~~~~~
> arch/x86/include/asm/string_32.h:150:25: note: in a call to built-in function '__builtin_memcpy'
> net/vmw_vsock/vmci_transport.c:164:17: note: in expansion of macro 'memcpy'
>   164 |                 memcpy(&pkt->u.wait, wait, sizeof(pkt->u.wait));
>       |                 ^~~~~~
> 
> This seems relatively harmless, and it so far the only instance of this
> warning I have found. The __vmci_transport_send_control_pkt function
> is called either with wait=NULL or with one of the type values that
> pass 'wait' into memcpy() here, but not from the same caller.
> 
> Replacing the memcpy with a struct assignment is otherwise the same
> but avoids the warning.
> 
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
>  net/vmw_vsock/vmci_transport.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/vmw_vsock/vmci_transport.c b/net/vmw_vsock/vmci_transport.c
> index 00f6bbdb035a..a64522be1bad 100644
> --- a/net/vmw_vsock/vmci_transport.c
> +++ b/net/vmw_vsock/vmci_transport.c
> @@ -161,7 +161,7 @@ vmci_transport_packet_init(struct vmci_transport_packet *pkt,
>  
>  	case VMCI_TRANSPORT_PACKET_TYPE_WAITING_READ:
>  	case VMCI_TRANSPORT_PACKET_TYPE_WAITING_WRITE:
> -		memcpy(&pkt->u.wait, wait, sizeof(pkt->u.wait));
> +		pkt->u.wait = *wait;
>  		break;
>  
>  	case VMCI_TRANSPORT_PACKET_TYPE_REQUEST2:
> -- 
> 2.39.5
> 

Reviewed-by: Bobby Eshleman <bobbyeshleman@xxxxxxxx>