-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);
+	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),
-		.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);
 
-- 
2.43.0

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

On 07/04/25 13:50, Kees Cook wrote:
> 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)?

Why not?

I mean, this should be equivalent to `TASK_COMM_LEN+16`, I could
use the latter if people prefer it (see my comments below).

> 
>> +	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?

Yes, it's just `2`. However, I didn't want to explicitly use the magic
number, in case people don't like it, as in other similar patches (in
other subsystems).

But, yeah, it's `2`. :)

Thanks
--
Gustavo

> 
>> -		.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
>

On Mon, Apr 07, 2025 at 01:57:48PM -0600, Gustavo A. R. Silva wrote:
> 
> 
> On 07/04/25 13:50, Kees Cook wrote:
> > 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)?
> 
> Why not?

Uhm, I'm genuinely curious. I *think* it will work, but because it's
within the struct, not outside of it, I'm unclear if it'll DTRT for
finding the size (since __builtin_object_size() can be touchy).

> I mean, this should be equivalent to `TASK_COMM_LEN+16`, I could
> use the latter if people prefer it (see my comments below).

Right, it should be the same. I think __struct_size(args->name) would be
much more readable ... if it works. :)

> 
> > 
> > > +	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?
> 
> Yes, it's just `2`. However, I didn't want to explicitly use the magic
> number, in case people don't like it, as in other similar patches (in
> other subsystems).
> 
> But, yeah, it's `2`. :)

Okay. So if "count" is set up as a counted_by, the assignment will
happen automatically (in DEFINE_FLEX -- no longer "RAW").

> 
> Thanks
> --
> Gustavo
> 
> > 
> > > -		.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

[..]

>>>> -	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)?
>>
>> Why not?
> 
> Uhm, I'm genuinely curious. I *think* it will work, but because it's
> within the struct, not outside of it, I'm unclear if it'll DTRT for
> finding the size (since __builtin_object_size() can be touchy).
> 
>> I mean, this should be equivalent to `TASK_COMM_LEN+16`, I could
>> use the latter if people prefer it (see my comments below).
> 
> Right, it should be the same. I think __struct_size(args->name) would be
> much more readable ... if it works. :)

OK, I'll double check this.

[..]

>>>> @@ -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?
>>
>> Yes, it's just `2`. However, I didn't want to explicitly use the magic
>> number, in case people don't like it, as in other similar patches (in
>> other subsystems).
>>
>> But, yeah, it's `2`. :)
> 
> Okay. So if "count" is set up as a counted_by, the assignment will
> happen automatically (in DEFINE_FLEX -- no longer "RAW").

I really don't want to condition -Wflex-array-member-not-at-end patches
on counted_by patches, for now.

Thanks
--
Gustavo

On Mon, Apr 07, 2025 at 05:35:47PM -0600, Gustavo A. R. Silva wrote:
> [..]
> 
> > > > > -	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)?
> > > 
> > > Why not?
> > 
> > Uhm, I'm genuinely curious. I *think* it will work, but because it's
> > within the struct, not outside of it, I'm unclear if it'll DTRT for
> > finding the size (since __builtin_object_size() can be touchy).
> > 
> > > I mean, this should be equivalent to `TASK_COMM_LEN+16`, I could
> > > use the latter if people prefer it (see my comments below).
> > 
> > Right, it should be the same. I think __struct_size(args->name) would be
> > much more readable ... if it works. :)
> 
> OK, I'll double check this.

Ah-ha, yes, I'm already testing this with KUnit:

struct bar {
        int a;
        u32 counter;
        s16 array[];
};
...
        DEFINE_RAW_FLEX(struct bar, two, array, 2);
	...
        KUNIT_EXPECT_EQ(test, sizeof(*two), sizeof(struct bar));
        KUNIT_EXPECT_EQ(test, __struct_size(two), sizeof(struct bar) + 2 * sizeof(s16));
        KUNIT_EXPECT_EQ(test, __member_size(two), sizeof(struct bar) + 2 * sizeof(s16));
        KUNIT_EXPECT_EQ(test, __struct_size(two->array), 2 * sizeof(s16));
        KUNIT_EXPECT_EQ(test, __member_size(two->array), 2 * sizeof(s16));


> I really don't want to condition -Wflex-array-member-not-at-end patches
> on counted_by patches, for now.

Fair enough. :) One thing at a time is wise!

-- 
Kees Cook

On 08/04/25 17:40, Kees Cook wrote:
> On Mon, Apr 07, 2025 at 05:35:47PM -0600, Gustavo A. R. Silva wrote:
>> [..]
>>
>>>>>> -	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)?
>>>>
>>>> Why not?
>>>
>>> Uhm, I'm genuinely curious. I *think* it will work, but because it's
>>> within the struct, not outside of it, I'm unclear if it'll DTRT for
>>> finding the size (since __builtin_object_size() can be touchy).
>>>
>>>> I mean, this should be equivalent to `TASK_COMM_LEN+16`, I could
>>>> use the latter if people prefer it (see my comments below).
>>>
>>> Right, it should be the same. I think __struct_size(args->name) would be
>>> much more readable ... if it works. :)
>>
>> OK, I'll double check this.
> 
> Ah-ha, yes, I'm already testing this with KUnit:
> 
> struct bar {
>          int a;
>          u32 counter;
>          s16 array[];
> };
> ...
>          DEFINE_RAW_FLEX(struct bar, two, array, 2);
> 	...
>          KUNIT_EXPECT_EQ(test, sizeof(*two), sizeof(struct bar));
>          KUNIT_EXPECT_EQ(test, __struct_size(two), sizeof(struct bar) + 2 * sizeof(s16));
>          KUNIT_EXPECT_EQ(test, __member_size(two), sizeof(struct bar) + 2 * sizeof(s16));
>          KUNIT_EXPECT_EQ(test, __struct_size(two->array), 2 * sizeof(s16));
>          KUNIT_EXPECT_EQ(test, __member_size(two->array), 2 * sizeof(s16));

Nice! I was taking a look at this, and now I want to use __member_size(p->array)
instead of __struct_size(p->array). ^.^

> 
> 
>> I really don't want to condition -Wflex-array-member-not-at-end patches
>> on counted_by patches, for now.
> 
> Fair enough. :) One thing at a time is wise!
> 

\o/

--
Gustavo