Re: [PATCH v6 01/14] drm/panthor: Add uAPI

[Erik Faye-Lund <erik.faye-lund@collabora.com>]

On Thu, 2024-02-29 at 17:22 +0100, Boris Brezillon wrote:
> +/**
> + * enum drm_panthor_sync_op_flags - Synchronization operation flags.
> + */
> +enum drm_panthor_sync_op_flags {
> +	/** @DRM_PANTHOR_SYNC_OP_HANDLE_TYPE_MASK: Synchronization
> handle type mask. */
> +	DRM_PANTHOR_SYNC_OP_HANDLE_TYPE_MASK = 0xff,
> +
> +	/** @DRM_PANTHOR_SYNC_OP_HANDLE_TYPE_SYNCOBJ:
> Synchronization object type. */
> +	DRM_PANTHOR_SYNC_OP_HANDLE_TYPE_SYNCOBJ = 0,
> +
> +	/**
> +	 * @DRM_PANTHOR_SYNC_OP_HANDLE_TYPE_TIMELINE_SYNCOBJ:
> Timeline synchronization
> +	 * object type.
> +	 */
> +	DRM_PANTHOR_SYNC_OP_HANDLE_TYPE_TIMELINE_SYNCOBJ = 1,
> +
> +	/** @DRM_PANTHOR_SYNC_OP_WAIT: Wait operation. */
> +	DRM_PANTHOR_SYNC_OP_WAIT = 0 << 31,
> +
> +	/** @DRM_PANTHOR_SYNC_OP_SIGNAL: Signal operation. */
> +	DRM_PANTHOR_SYNC_OP_SIGNAL = (int)(1u << 31),

Why do we cast to int here? 1u << 31 doesn't fit in a 32-bit signed
integer, so isn't this undefined behavior in C?

I'm asking, because Coverity complains about overflows when we assign
the value to drm_panthor_sync_op::flags in Mesa, and looking at it...
it seems to be right in complaining!

For reference, here's the Coverity issue (requires login,
unfortunately):
https://scan5.scan.coverity.com/#/project-view/59795/10037?selectedIssue=1605083