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

Gustavo A. R. Silva
2025-04-07T19:57:52Z

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
>