Nouveau - Apr 2025 - [PATCH][next] drm/nouveau: fifo: Avoid -Wflex-array-member-not-at-end warning

-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/nvif/fifo.c:29:42: 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 at kernel.org>
---
 drivers/gpu/drm/nouveau/nvif/fifo.c | 32 ++++++++++++-----------------
 1 file changed, 13 insertions(+), 19 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nvif/fifo.c
b/drivers/gpu/drm/nouveau/nvif/fifo.c
index a463289962b2..f8772340fec4 100644
--- a/drivers/gpu/drm/nouveau/nvif/fifo.c
+++ b/drivers/gpu/drm/nouveau/nvif/fifo.c
@@ -25,33 +25,28 @@ static int
 nvif_fifo_runlists(struct nvif_device *device)
 {
 	struct nvif_object *object = &device->object;
-	struct {
-		struct nv_device_info_v1 m;
-		struct {
-			struct nv_device_info_v1_data runlists;
-			struct nv_device_info_v1_data runlist[64];
-		} v;
-	} *a;
+	DEFINE_RAW_FLEX(struct nv_device_info_v1, a, data, 65);
+	struct nv_device_info_v1_data *runlists = &a->data[0];
+	struct nv_device_info_v1_data *runlist = &a->data[1];
+	const u8 rl_cnt = (__struct_size(a) - sizeof(*a)) / sizeof(*a->data) - 1;
 	int ret, i;
 
 	if (device->runlist)
 		return 0;
 
-	if (!(a = kmalloc(sizeof(*a), GFP_KERNEL)))
-		return -ENOMEM;
-	a->m.version = 1;
-	a->m.count = sizeof(a->v) / sizeof(a->v.runlists);
-	a->v.runlists.mthd = NV_DEVICE_HOST_RUNLISTS;
-	for (i = 0; i < ARRAY_SIZE(a->v.runlist); i++) {
-		a->v.runlist[i].mthd = NV_DEVICE_HOST_RUNLIST_ENGINES;
-		a->v.runlist[i].data = i;
+	a->version = 1;
+	a->count = (__struct_size(a) - sizeof(*a)) / sizeof(*a->data);
+	runlists->mthd = NV_DEVICE_HOST_RUNLISTS;
+	for (i = 0; i < rl_cnt; i++) {
+		runlist[i].mthd = NV_DEVICE_HOST_RUNLIST_ENGINES;
+		runlist[i].data = i;
 	}
 
 	ret = nvif_object_mthd(object, NV_DEVICE_V0_INFO, a, sizeof(*a));
 	if (ret)
 		goto done;
 
-	device->runlists = fls64(a->v.runlists.data);
+	device->runlists = fls64(runlists->data);
 	device->runlist = kcalloc(device->runlists, sizeof(*device->runlist),
 				  GFP_KERNEL);
 	if (!device->runlist) {
@@ -60,12 +55,11 @@ nvif_fifo_runlists(struct nvif_device *device)
 	}
 
 	for (i = 0; i < device->runlists; i++) {
-		if (a->v.runlist[i].mthd != NV_DEVICE_INFO_INVALID)
-			device->runlist[i].engines = a->v.runlist[i].data;
+		if (runlist[i].mthd != NV_DEVICE_INFO_INVALID)
+			device->runlist[i].engines = runlist[i].data;
 	}
 
 done:
-	kfree(a);
 	return ret;
 }
 
-- 
2.43.0

On 03/04/25 11:41, 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/nvif/fifo.c:29:42: 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 at kernel.org>
> ---
>   drivers/gpu/drm/nouveau/nvif/fifo.c | 32 ++++++++++++-----------------
>   1 file changed, 13 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nvif/fifo.c
b/drivers/gpu/drm/nouveau/nvif/fifo.c
> index a463289962b2..f8772340fec4 100644
> --- a/drivers/gpu/drm/nouveau/nvif/fifo.c
> +++ b/drivers/gpu/drm/nouveau/nvif/fifo.c
> @@ -25,33 +25,28 @@ static int
>   nvif_fifo_runlists(struct nvif_device *device)
>   {
>   	struct nvif_object *object = &device->object;
> -	struct {
> -		struct nv_device_info_v1 m;
> -		struct {
> -			struct nv_device_info_v1_data runlists;
> -			struct nv_device_info_v1_data runlist[64];
> -		} v;
> -	} *a;
> +	DEFINE_RAW_FLEX(struct nv_device_info_v1, a, data, 65);
> +	struct nv_device_info_v1_data *runlists = &a->data[0];
> +	struct nv_device_info_v1_data *runlist = &a->data[1];
> +	const u8 rl_cnt = (__struct_size(a) - sizeof(*a)) / sizeof(*a->data) -
1;
>   	int ret, i;
>   
>   	if (device->runlist)
>   		return 0;
>   
> -	if (!(a = kmalloc(sizeof(*a), GFP_KERNEL)))
I'll send v2 preserving the above allocation (with some adjustments to
remove the flex-array-in-the-middle issue), as I just got this report
from the kernel test robot:

https://lore.kernel.org/lkml/202504041254.6e26LBdj-lkp at intel.com/

Thanks
--
Gustavo