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

[Stefano Garzarella <sgarzare@redhat.com>]

On Tue, Feb 03, 2026 at 05:34:00PM +0100, Arnd Bergmann wrote:
>From: Arnd Bergmann <arnd@arndb.de>
>
>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@arndb.de>
>---
> net/vmw_vsock/vmci_transport.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)

Not sure if it's net or net-next material, maybe net to avoid the 
warning/error on v6.19 too ?

Anyway LGTM and thanks for the fix!

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>

>
>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
>