linux-kernel - Re: [PATCH][next] drm/nouveau: fence: Avoid -Wflex-array-member-not-at-end warning

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Message-ID: <202504071223.EDBF8A080@keescook>
Date: Mon, 7 Apr 2025 12:23:55 -0700
From: Kees Cook <kees@...nel.org>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Lyude Paul <lyude@...hat.com>, Danilo Krummrich <dakr@...nel.org>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	dri-devel@...ts.freedesktop.org, nouveau@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] drm/nouveau: fence: Avoid
 -Wflex-array-member-not-at-end warning

On Wed, Apr 02, 2025 at 03:28:10PM -0600, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> getting ready to enable it, globally.
> 
> Use the `DEFINE_RAW_FLEX()` helper for an on-stack definition of
> a flexible structure where the size of the flexible-array member
> is known at compile-time, and refactor the rest of the code,
> accordingly.
> 
> So, with these changes, fix the following warning:
> 
> drivers/gpu/drm/nouveau/nouveau_fence.c:188:38: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
>  drivers/gpu/drm/nouveau/nouveau_fence.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c b/drivers/gpu/drm/nouveau/nouveau_fence.c
> index 7cc84472cece..7622587f149e 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_fence.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_fence.c
> @@ -184,10 +184,10 @@ nouveau_fence_context_new(struct nouveau_channel *chan, struct nouveau_fence_cha
>  	struct nouveau_cli *cli = chan->cli;
>  	struct nouveau_drm *drm = cli->drm;
>  	struct nouveau_fence_priv *priv = (void*)drm->fence;
> -	struct {
> -		struct nvif_event_v0 base;
> -		struct nvif_chan_event_v0 host;
> -	} args;
> +	DEFINE_RAW_FLEX(struct nvif_event_v0, args, data,
> +			sizeof(struct nvif_chan_event_v0));
> +	struct nvif_chan_event_v0 *host =
> +				(struct nvif_chan_event_v0 *)args->data;
>  	int ret;
>  
>  	INIT_WORK(&fctx->uevent_work, nouveau_fence_uevent_work);
> @@ -207,12 +207,12 @@ nouveau_fence_context_new(struct nouveau_channel *chan, struct nouveau_fence_cha
>  	if (!priv->uevent)
>  		return;
>  
> -	args.host.version = 0;
> -	args.host.type = NVIF_CHAN_EVENT_V0_NON_STALL_INTR;
> +	host->version = 0;
> +	host->type = NVIF_CHAN_EVENT_V0_NON_STALL_INTR;
>  
>  	ret = nvif_event_ctor(&chan->user, "fenceNonStallIntr", (chan->runlist << 16) | chan->chid,
>  			      nouveau_fence_wait_uevent_handler, false,
> -			      &args.base, sizeof(args), &fctx->event);
> +			      args, __struct_size(args), &fctx->event);
>  
>  	WARN_ON(ret);
>  }

Looks good to me. Good replacement, including the __struct_size() use.

Reviewed-by: Kees Cook <kees@...nel.org>

-- 
Kees Cook