Re: [PATCH][next] drm/nouveau: chan: Avoid -Wflex-array-member-not-at-end warnings

[Kees Cook <kees@kernel.org>]

On Thu, Apr 03, 2025 at 10:45:18AM -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 a few on-stack definitions
> 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 warnings:
> 
> drivers/gpu/drm/nouveau/nouveau_chan.c:274:37: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/gpu/drm/nouveau/nouveau_chan.c:371:46: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/gpu/drm/nouveau/nouveau_chan.c:524:42: 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@kernel.org>
> ---
>  drivers/gpu/drm/nouveau/nouveau_chan.c | 115 ++++++++++++-------------
>  1 file changed, 56 insertions(+), 59 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nouveau_chan.c b/drivers/gpu/drm/nouveau/nouveau_chan.c
> index cd659b9fd1d9..a7e70517b7cd 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_chan.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_chan.c
> @@ -270,10 +270,7 @@ nouveau_channel_ctor(struct nouveau_cli *cli, bool priv, u64 runm,
>  		{    NV03_CHANNEL_DMA     , 0 },
>  		{}
>  	};
> -	struct {
> -		struct nvif_chan_v0 chan;
> -		char name[TASK_COMM_LEN+16];
> -	} args;
> +	DEFINE_RAW_FLEX(struct nvif_chan_v0, args, name, TASK_COMM_LEN + 16);
>  	struct nvif_device *device = &cli->device;
>  	struct nouveau_channel *chan;
>  	const u64 plength = 0x10000;
> @@ -298,28 +295,28 @@ nouveau_channel_ctor(struct nouveau_cli *cli, bool priv, u64 runm,
>  		return ret;
>  
>  	/* create channel object */
> -	args.chan.version = 0;
> -	args.chan.namelen = sizeof(args.name);
> -	args.chan.runlist = __ffs64(runm);
> -	args.chan.runq = 0;
> -	args.chan.priv = priv;
> -	args.chan.devm = BIT(0);
> +	args->version = 0;
> +	args->namelen = __struct_size(args) - sizeof(*args);

Does __struct_size(args->name) work here (and later)?

> +	args->runlist = __ffs64(runm);
> +	args->runq = 0;
> +	args->priv = priv;
> +	args->devm = BIT(0);
>  	if (hosts[cid].oclass < NV50_CHANNEL_GPFIFO) {
> -		args.chan.vmm = 0;
> -		args.chan.ctxdma = nvif_handle(&chan->push.ctxdma);
> -		args.chan.offset = chan->push.addr;
> -		args.chan.length = 0;
> +		args->vmm = 0;
> +		args->ctxdma = nvif_handle(&chan->push.ctxdma);
> +		args->offset = chan->push.addr;
> +		args->length = 0;
>  	} else {
> -		args.chan.vmm = nvif_handle(&chan->vmm->vmm.object);
> +		args->vmm = nvif_handle(&chan->vmm->vmm.object);
>  		if (hosts[cid].oclass < FERMI_CHANNEL_GPFIFO)
> -			args.chan.ctxdma = nvif_handle(&chan->push.ctxdma);
> +			args->ctxdma = nvif_handle(&chan->push.ctxdma);
>  		else
> -			args.chan.ctxdma = 0;
> -		args.chan.offset = ioffset + chan->push.addr;
> -		args.chan.length = ilength;
> +			args->ctxdma = 0;
> +		args->offset = ioffset + chan->push.addr;
> +		args->length = ilength;
>  	}
> -	args.chan.huserd = 0;
> -	args.chan.ouserd = 0;
> +	args->huserd = 0;
> +	args->ouserd = 0;
>  
>  	/* allocate userd */
>  	if (hosts[cid].oclass >= VOLTA_CHANNEL_GPFIFO_A) {
> @@ -329,27 +326,28 @@ nouveau_channel_ctor(struct nouveau_cli *cli, bool priv, u64 runm,
>  		if (ret)
>  			return ret;
>  
> -		args.chan.huserd = nvif_handle(&chan->mem_userd.object);
> -		args.chan.ouserd = 0;
> +		args->huserd = nvif_handle(&chan->mem_userd.object);
> +		args->ouserd = 0;
>  
>  		chan->userd = &chan->mem_userd.object;
>  	} else {
>  		chan->userd = &chan->user;
>  	}
>  
> -	snprintf(args.name, sizeof(args.name), "%s[%d]", current->comm, task_pid_nr(current));
> +	snprintf(args->name, __struct_size(args) - sizeof(*args), "%s[%d]",
> +		 current->comm, task_pid_nr(current));
>  
>  	ret = nvif_object_ctor(&device->object, "abi16ChanUser", 0, hosts[cid].oclass,
> -			       &args, sizeof(args), &chan->user);
> +			       args, __struct_size(args), &chan->user);
>  	if (ret) {
>  		nouveau_channel_del(pchan);
>  		return ret;
>  	}
>  
> -	chan->runlist = args.chan.runlist;
> -	chan->chid = args.chan.chid;
> -	chan->inst = args.chan.inst;
> -	chan->token = args.chan.token;
> +	chan->runlist = args->runlist;
> +	chan->chid = args->chid;
> +	chan->inst = args->inst;
> +	chan->token = args->token;
>  	return 0;
>  }
>  
> @@ -367,17 +365,17 @@ nouveau_channel_init(struct nouveau_channel *chan, u32 vram, u32 gart)
>  		return ret;
>  
>  	if (chan->user.oclass >= FERMI_CHANNEL_GPFIFO) {
> -		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;
>  
> -		args.host.version = 0;
> -		args.host.type = NVIF_CHAN_EVENT_V0_KILLED;
> +		host->version = 0;
> +		host->type = NVIF_CHAN_EVENT_V0_KILLED;
>  
>  		ret = nvif_event_ctor(&chan->user, "abi16ChanKilled", chan->chid,
>  				      nouveau_channel_killed, false,
> -				      &args.base, sizeof(args), &chan->kill);
> +				      args, __struct_size(args), &chan->kill);
>  		if (ret == 0)
>  			ret = nvif_event_allow(&chan->kill);
>  		if (ret) {
> @@ -520,46 +518,45 @@ nouveau_channels_fini(struct nouveau_drm *drm)
>  int
>  nouveau_channels_init(struct nouveau_drm *drm)
>  {
> -	struct {
> -		struct nv_device_info_v1 m;
> -		struct {
> -			struct nv_device_info_v1_data channels;
> -			struct nv_device_info_v1_data runlists;
> -		} v;
> -	} args = {
> -		.m.version = 1,
> -		.m.count = sizeof(args.v) / sizeof(args.v.channels),

sizeof(args.v) == sizeof(struct nv_device_info_v1_data) * 2

and sizeof(args.v.channels) == sizeof(struct nv_device_info_v1_data).

Isn't this just "2"? i.e. isn't struct nv_device_info_v1::count the
counted_by for struct nv_device_info_v1::data?

> -		.v.channels.mthd = NV_DEVICE_HOST_CHANNELS,
> -		.v.runlists.mthd = NV_DEVICE_HOST_RUNLISTS,
> -	};
> +	DEFINE_RAW_FLEX(struct nv_device_info_v1, args, data, 2);
> +	struct nv_device_info_v1_data *channels = &args->data[0];
> +	struct nv_device_info_v1_data *runlists = &args->data[1];
>  	struct nvif_object *device = &drm->client.device.object;
>  	int ret, i;
>  
> -	ret = nvif_object_mthd(device, NV_DEVICE_V0_INFO, &args, sizeof(args));
> +	args->version = 1;
> +	args->count = (__struct_size(args) - sizeof(*args)) /
> +		      sizeof(*args->data);
> +	channels->mthd = NV_DEVICE_HOST_CHANNELS;
> +	runlists->mthd = NV_DEVICE_HOST_RUNLISTS;
> +
> +	ret = nvif_object_mthd(device, NV_DEVICE_V0_INFO, args,
> +			       __struct_size(args));
>  	if (ret ||
> -	    args.v.runlists.mthd == NV_DEVICE_INFO_INVALID || !args.v.runlists.data ||
> -	    args.v.channels.mthd == NV_DEVICE_INFO_INVALID)
> +	    runlists->mthd == NV_DEVICE_INFO_INVALID || !runlists->data ||
> +	    channels->mthd == NV_DEVICE_INFO_INVALID)
>  		return -ENODEV;
>  
> -	drm->chan_nr = drm->chan_total = args.v.channels.data;
> -	drm->runl_nr = fls64(args.v.runlists.data);
> +	drm->chan_nr = drm->chan_total = channels->data;
> +	drm->runl_nr = fls64(runlists->data);
>  	drm->runl = kcalloc(drm->runl_nr, sizeof(*drm->runl), GFP_KERNEL);
>  	if (!drm->runl)
>  		return -ENOMEM;
>  
>  	if (drm->chan_nr == 0) {
>  		for (i = 0; i < drm->runl_nr; i++) {
> -			if (!(args.v.runlists.data & BIT(i)))
> +			if (!(runlists->data & BIT(i)))
>  				continue;
>  
> -			args.v.channels.mthd = NV_DEVICE_HOST_RUNLIST_CHANNELS;
> -			args.v.channels.data = i;
> +			channels->mthd = NV_DEVICE_HOST_RUNLIST_CHANNELS;
> +			channels->data = i;
>  
> -			ret = nvif_object_mthd(device, NV_DEVICE_V0_INFO, &args, sizeof(args));
> -			if (ret || args.v.channels.mthd == NV_DEVICE_INFO_INVALID)
> +			ret = nvif_object_mthd(device, NV_DEVICE_V0_INFO, args,
> +					       __struct_size(args));
> +			if (ret || channels->mthd == NV_DEVICE_INFO_INVALID)
>  				return -ENODEV;
>  
> -			drm->runl[i].chan_nr = args.v.channels.data;
> +			drm->runl[i].chan_nr = channels->data;
>  			drm->runl[i].chan_id_base = drm->chan_total;
>  			drm->runl[i].context_base = dma_fence_context_alloc(drm->runl[i].chan_nr);
>  

Otherwise looks good.

-Kees

-- 
Kees Cook