Nouveau - Aug 2024 - [PATCH][next] drm/nouveau: Avoid -Wflex-array-member-not-at-end warning

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 this, fix the following warning:

drivers/gpu/drm/nouveau/dispnv50/disp.c:779:47: 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/dispnv50/disp.c | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c
b/drivers/gpu/drm/nouveau/dispnv50/disp.c
index eed579a6c858..ddddc69640be 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
@@ -774,11 +774,9 @@ nv50_hdmi_enable(struct drm_encoder *encoder, struct
nouveau_crtc *nv_crtc,
 	struct drm_hdmi_info *hdmi = &nv_connector->base.display_info.hdmi;
 	union hdmi_infoframe infoframe = { 0 };
 	const u8 rekey = 56; /* binary driver, and tegra, constant */
+	DEFINE_RAW_FLEX(struct nvif_outp_infoframe_v0, args, data, 17);
+	const u8 data_len = 17; /* same length as in DEFINE_RAW_FLEX above. */
 	u32 max_ac_packet;
-	struct {
-		struct nvif_outp_infoframe_v0 infoframe;
-		u8 data[17];
-	} args = { 0 };
 	int ret, size;
 
 	max_ac_packet  = mode->htotal - mode->hdisplay;
@@ -815,29 +813,29 @@ nv50_hdmi_enable(struct drm_encoder *encoder, struct
nouveau_crtc *nv_crtc,
 		return;
 
 	/* AVI InfoFrame. */
-	args.infoframe.version = 0;
-	args.infoframe.head = nv_crtc->index;
+	args->version = 0;
+	args->head = nv_crtc->index;
 
 	if (!drm_hdmi_avi_infoframe_from_display_mode(&infoframe.avi,
&nv_connector->base, mode)) {
 		drm_hdmi_avi_infoframe_quant_range(&infoframe.avi,
&nv_connector->base, mode,
 						   HDMI_QUANTIZATION_RANGE_FULL);
 
-		size = hdmi_infoframe_pack(&infoframe, args.data, ARRAY_SIZE(args.data));
+		size = hdmi_infoframe_pack(&infoframe, args->data, data_len);
 	} else {
 		size = 0;
 	}
 
-	nvif_outp_infoframe(&nv_encoder->outp, NVIF_OUTP_INFOFRAME_V0_AVI,
&args.infoframe, size);
+	nvif_outp_infoframe(&nv_encoder->outp, NVIF_OUTP_INFOFRAME_V0_AVI,
args, size);
 
 	/* Vendor InfoFrame. */
-	memset(&args.data, 0, sizeof(args.data));
+	memset(args->data, 0, data_len);
 	if (!drm_hdmi_vendor_infoframe_from_display_mode(&infoframe.vendor.hdmi,
 							 &nv_connector->base, mode))
-		size = hdmi_infoframe_pack(&infoframe, args.data, ARRAY_SIZE(args.data));
+		size = hdmi_infoframe_pack(&infoframe, args->data, data_len);
 	else
 		size = 0;
 
-	nvif_outp_infoframe(&nv_encoder->outp, NVIF_OUTP_INFOFRAME_V0_VSI,
&args.infoframe, size);
+	nvif_outp_infoframe(&nv_encoder->outp, NVIF_OUTP_INFOFRAME_V0_VSI,
args, size);
 
 	nv_encoder->hdmi.enabled = true;
 }
-- 
2.34.1

On Wed, Aug 21, 2024 at 02:16:21PM -0600, Gustavo A. R. Silva
wrote:
> 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 this, fix the following warning:
> 
> drivers/gpu/drm/nouveau/dispnv50/disp.c:779:47: 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/dispnv50/disp.c | 20 +++++++++-----------
>  1 file changed, 9 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c
b/drivers/gpu/drm/nouveau/dispnv50/disp.c
> index eed579a6c858..ddddc69640be 100644
> --- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
> +++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
> @@ -774,11 +774,9 @@ nv50_hdmi_enable(struct drm_encoder *encoder, struct
nouveau_crtc *nv_crtc,
>  	struct drm_hdmi_info *hdmi =
&nv_connector->base.display_info.hdmi;
>  	union hdmi_infoframe infoframe = { 0 };
>  	const u8 rekey = 56; /* binary driver, and tegra, constant */
> +	DEFINE_RAW_FLEX(struct nvif_outp_infoframe_v0, args, data, 17);
> +	const u8 data_len = 17; /* same length as in DEFINE_RAW_FLEX above. */
To avoid repeating the open-coded "17", this could either be a define:

nv50_hdmi_enable(...)
{
...
#define data_len	17
	DEFINE_RAW_FLEX(struct nvif_outp_infoframe_v0, args, data, data_len);
...rest of function...
#undef data_len
}

or an ungainly but compile-time calculated value that exposes some
DEFINE_FLEX internals:

	const u8 data_len = (sizeof(args_u) - sizeof(*args)) / sizeof(*args->data);

(Maybe a helper is needed for that?)

#define STACK_FLEX_COUNT(name, member)	\
	((sizeof(name##_u) = sizeof(*(name))) / sizeof(*(name)->member))
> @@ -815,29 +813,29 @@ nv50_hdmi_enable(struct drm_encoder *encoder, struct
nouveau_crtc *nv_crtc,
>  		return;
>  
>  	/* AVI InfoFrame. */
> -	args.infoframe.version = 0;
> -	args.infoframe.head = nv_crtc->index;
> +	args->version = 0;
> +	args->head = nv_crtc->index;
The stack variable (was before and is again) already zero-initialized,
so the "= 0" line shouldn't be needed.

But neither of these comments are show-stoppers, IMO.

Reviewed-by: Kees Cook <kees at kernel.org>

-- 
Kees Cook

Hi all,

Friendly ping: who can take this, please? ?

Thanks
-Gustavo

On 21/08/24 22:16, Gustavo A. R. Silva wrote:
> 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 this, fix the following warning:
> 
> drivers/gpu/drm/nouveau/dispnv50/disp.c:779:47: 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/dispnv50/disp.c | 20 +++++++++-----------
>   1 file changed, 9 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c
b/drivers/gpu/drm/nouveau/dispnv50/disp.c
> index eed579a6c858..ddddc69640be 100644
> --- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
> +++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
> @@ -774,11 +774,9 @@ nv50_hdmi_enable(struct drm_encoder *encoder, struct
nouveau_crtc *nv_crtc,
>   	struct drm_hdmi_info *hdmi =
&nv_connector->base.display_info.hdmi;
>   	union hdmi_infoframe infoframe = { 0 };
>   	const u8 rekey = 56; /* binary driver, and tegra, constant */
> +	DEFINE_RAW_FLEX(struct nvif_outp_infoframe_v0, args, data, 17);
> +	const u8 data_len = 17; /* same length as in DEFINE_RAW_FLEX above. */
>   	u32 max_ac_packet;
> -	struct {
> -		struct nvif_outp_infoframe_v0 infoframe;
> -		u8 data[17];
> -	} args = { 0 };
>   	int ret, size;
>   
>   	max_ac_packet  = mode->htotal - mode->hdisplay;
> @@ -815,29 +813,29 @@ nv50_hdmi_enable(struct drm_encoder *encoder, struct
nouveau_crtc *nv_crtc,
>   		return;
>   
>   	/* AVI InfoFrame. */
> -	args.infoframe.version = 0;
> -	args.infoframe.head = nv_crtc->index;
> +	args->version = 0;
> +	args->head = nv_crtc->index;
>   
>   	if (!drm_hdmi_avi_infoframe_from_display_mode(&infoframe.avi,
&nv_connector->base, mode)) {
>   		drm_hdmi_avi_infoframe_quant_range(&infoframe.avi,
&nv_connector->base, mode,
>   						   HDMI_QUANTIZATION_RANGE_FULL);
>   
> -		size = hdmi_infoframe_pack(&infoframe, args.data,
ARRAY_SIZE(args.data));
> +		size = hdmi_infoframe_pack(&infoframe, args->data, data_len);
>   	} else {
>   		size = 0;
>   	}
>   
> -	nvif_outp_infoframe(&nv_encoder->outp, NVIF_OUTP_INFOFRAME_V0_AVI,
&args.infoframe, size);
> +	nvif_outp_infoframe(&nv_encoder->outp, NVIF_OUTP_INFOFRAME_V0_AVI,
args, size);
>   
>   	/* Vendor InfoFrame. */
> -	memset(&args.data, 0, sizeof(args.data));
> +	memset(args->data, 0, data_len);
>   	if
(!drm_hdmi_vendor_infoframe_from_display_mode(&infoframe.vendor.hdmi,
>   							 &nv_connector->base, mode))
> -		size = hdmi_infoframe_pack(&infoframe, args.data,
ARRAY_SIZE(args.data));
> +		size = hdmi_infoframe_pack(&infoframe, args->data, data_len);
>   	else
>   		size = 0;
>   
> -	nvif_outp_infoframe(&nv_encoder->outp, NVIF_OUTP_INFOFRAME_V0_VSI,
&args.infoframe, size);
> +	nvif_outp_infoframe(&nv_encoder->outp, NVIF_OUTP_INFOFRAME_V0_VSI,
args, size);
>   
>   	nv_encoder->hdmi.enabled = true;
>   }