Re: [PATCH for-4.15 5/5] tools/xenstored: Silence coverity when using xs_state_* structures

[Jürgen Groß <jgross@xxxxxxxx>]

On 25.02.21 18:41, Julien Grall wrote:
> From: Julien Grall <jgrall@xxxxxxxxxx>
>
> Coverity will report unitialized values for every use of xs_state_*
> structures in the save part. This can be prevented by using the [0]
> rather than [] to define variable length array.
>
> Coverity-ID: 1472398
> Coverity-ID: 1472397
> Coverity-ID: 1472396
> Coverity-ID: 1472395
> Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
Sorry, but Coverity is clearly wrong here.

Should we really modify our code to work around bugs in external
static code analyzers?


Juergen

> ---
>
>  From my understanding, the tools and the hypervisor already rely on GNU
> extensions. So the change should be fine.
>
> If not, we can use the same approach as XEN_FLEX_ARRAY_DIM.
> ---
>   tools/xenstore/include/xenstore_state.h | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/tools/xenstore/include/xenstore_state.h 
> b/tools/xenstore/include/xenstore_state.h
> index ae0d053c8ffc..407d9e920c0f 100644
> --- a/tools/xenstore/include/xenstore_state.h
> +++ b/tools/xenstore/include/xenstore_state.h
> @@ -86,7 +86,7 @@ struct xs_state_connection {
>       uint16_t data_in_len;    /* Number of unprocessed bytes read from conn. */
>       uint16_t data_resp_len;  /* Size of partial response pending for conn. */
>       uint32_t data_out_len;   /* Number of bytes not yet written to conn. */
> -    uint8_t  data[];         /* Pending data (read, written) + 0-7 pad bytes. 
> */
> +    uint8_t  data[0];         /* Pending data (read, written) + 0-7 pad bytes. 
> */
>   };
>   
>   /* Watch: */
> @@ -94,7 +94,7 @@ struct xs_state_watch {
>       uint32_t conn_id;       /* Connection this watch is associated with. */
>       uint16_t path_length;   /* Number of bytes of path watched (incl. 0). */
>       uint16_t token_length;  /* Number of bytes of watch token (incl. 0). */
> -    uint8_t data[];         /* Path bytes, token bytes, 0-7 pad bytes. */
> +    uint8_t data[0];        /* Path bytes, token bytes, 0-7 pad bytes. */
>   };
>   
>   /* Transaction: */
> @@ -125,7 +125,7 @@ struct xs_state_node {
>   #define XS_STATE_NODE_TA_WRITTEN  0x0002
>       uint16_t perm_n;        /* Number of permissions (0 in TA: node deleted). 
> */
>       /* Permissions (first is owner, has full access). */
> -    struct xs_state_node_perm perms[];
> +    struct xs_state_node_perm perms[0];
>       /* Path and data follows, plus 0-7 pad bytes. */
>   };
>   #endif /* XENSTORE_STATE_H */

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