Linux Virtualization - Apr 2016 - [PATCH] virtio: fix "warning: ‘queue’ may be used uninitialized"

This fixes the following warning:
drivers/virtio/virtio_ring.c:1032:5: warning: ?queue? may be used
uninitialized in this function

The conditions that govern when queue is set aren't apparent to gcc.

Setting queue = NULL clears the warning.

Signed-off-by: Jeff Mahoney <jeffm at suse.com>
---

 drivers/virtio/virtio_ring.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1006,7 +1006,7 @@ struct virtqueue *vring_create_virtqueue
 	const char *name)
 {
 	struct virtqueue *vq;
-	void *queue;
+	void *queue = NULL;
 	dma_addr_t dma_addr;
 	size_t queue_size_in_bytes;
 	struct vring vring;

-- 
Jeff Mahoney
SUSE Labs

On Mon, Apr 04, 2016 at 02:14:19PM -0400, Jeff Mahoney
wrote:
> This fixes the following warning:
> drivers/virtio/virtio_ring.c:1032:5: warning: ?queue? may be used
> uninitialized in this function
> 
> The conditions that govern when queue is set aren't apparent to gcc.
> 
> Setting queue = NULL clears the warning.
> 
> Signed-off-by: Jeff Mahoney <jeffm at suse.com>
Which gcc version produces this warning?
I do not seem to see it with gcc 5.3.1.
Also - use uninitialized_var then?
> ---
> 
>  drivers/virtio/virtio_ring.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -1006,7 +1006,7 @@ struct virtqueue *vring_create_virtqueue
>  	const char *name)
>  {
>  	struct virtqueue *vq;
> -	void *queue;
> +	void *queue = NULL;
>  	dma_addr_t dma_addr;
>  	size_t queue_size_in_bytes;
>  	struct vring vring;
> 
> -- 
> Jeff Mahoney
> SUSE Labs

On 4/5/16 4:04 AM, Michael S. Tsirkin wrote:
> On Mon, Apr 04, 2016 at 02:14:19PM -0400, Jeff Mahoney wrote:
>> This fixes the following warning:
>> drivers/virtio/virtio_ring.c:1032:5: warning: ?queue? may be used
>> uninitialized in this function
>>
>> The conditions that govern when queue is set aren't apparent to
gcc.
>>
>> Setting queue = NULL clears the warning.
>>
>> Signed-off-by: Jeff Mahoney <jeffm at suse.com>
> 
> Which gcc version produces this warning?
> I do not seem to see it with gcc 5.3.1.
gcc version 4.8.5 (SUSE Linux)
> Also - use uninitialized_var then?
If it were a fast path, sure, but otherwise the use of uninitialized_var
just makes similar issues harder to debug if the code changes.

-Jeff
>> ---
>>
>>  drivers/virtio/virtio_ring.c |    2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> --- a/drivers/virtio/virtio_ring.c
>> +++ b/drivers/virtio/virtio_ring.c
>> @@ -1006,7 +1006,7 @@ struct virtqueue *vring_create_virtqueue
>>  	const char *name)
>>  {
>>  	struct virtqueue *vq;
>> -	void *queue;
>> +	void *queue = NULL;
>>  	dma_addr_t dma_addr;
>>  	size_t queue_size_in_bytes;
>>  	struct vring vring;
>>
>> -- 
>> Jeff Mahoney
>> SUSE Labs
> 

-- 
Jeff Mahoney
SUSE Labs

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