Nouveau - Mar 2025 - [PATCH v2][next] drm/nouveau/outp: 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/outp.c:199:45: 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>
---
Changes in v2:
 - Avoid using magic number in if statement. (Danilo)
 - Use sizeof() instead of __struct_size().

v1:
 - Link: https://lore.kernel.org/linux-hardening/Z-a2DAQmcsHHlyci at kspp/

 drivers/gpu/drm/nouveau/nvif/outp.c | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nvif/outp.c
b/drivers/gpu/drm/nouveau/nvif/outp.c
index 6daeb7f0b09b..1ea20b2bdd29 100644
--- a/drivers/gpu/drm/nouveau/nvif/outp.c
+++ b/drivers/gpu/drm/nouveau/nvif/outp.c
@@ -195,20 +195,17 @@ nvif_outp_dp_aux_pwr(struct nvif_outp *outp, bool enable)
 int
 nvif_outp_hda_eld(struct nvif_outp *outp, int head, void *data, u32 size)
 {
-	struct {
-		struct nvif_outp_hda_eld_v0 mthd;
-		u8 data[128];
-	} args;
+	DEFINE_RAW_FLEX(struct nvif_outp_hda_eld_v0, mthd, data, 128);
 	int ret;
 
-	if (WARN_ON(size > ARRAY_SIZE(args.data)))
+	if (WARN_ON(size > (__struct_size(mthd) - sizeof(*mthd))))
 		return -EINVAL;
 
-	args.mthd.version = 0;
-	args.mthd.head = head;
+	mthd->version = 0;
+	mthd->head = head;
 
-	memcpy(args.data, data, size);
-	ret = nvif_mthd(&outp->object, NVIF_OUTP_V0_HDA_ELD, &args,
sizeof(args.mthd) + size);
+	memcpy(mthd->data, data, size);
+	ret = nvif_mthd(&outp->object, NVIF_OUTP_V0_HDA_ELD, mthd,
sizeof(*mthd) + size);
 	NVIF_ERRON(ret, &outp->object, "[HDA_ELD head:%d size:%d]",
head, size);
 	return ret;
 }
-- 
2.43.0

On Fri, Mar 28, 2025 at 09:52:18AM -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 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/outp.c:199:45: 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>
> ---
> Changes in v2:
>  - Avoid using magic number in if statement. (Danilo)
>  - Use sizeof() instead of __struct_size().
Good catch -- I guess the original code should have been a bit more obvious by
passing &args.mthd, rather than &args.

Applied to drm-misc-next, thanks!