2020-11-03 22:18:13

by Lyude Paul

Subject: [PATCH v2] drm/edid: Fix uninitialized variable in drm_cvt_modes()

Noticed this when trying to compile with -Wall on a kernel fork. We potentially
don't set width here, which causes the compiler to complain about width
potentially being uninitialized in drm_cvt_modes(). So, let's fix that.

Changes since v1:
* Don't emit an error as this code isn't reachable, just mark it as such

Signed-off-by: Lyude Paul <[email protected]>

Cc: <[email protected]> # v5.9+
Fixes: 3f649ab728cd ("treewide: Remove uninitialized_var() usage")
Signed-off-by: Lyude Paul <[email protected]>
---
drivers/gpu/drm/drm_edid.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 631125b46e04..0643b98c6383 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -3094,6 +3094,7 @@ static int drm_cvt_modes(struct drm_connector *connector,

for (i = 0; i < 4; i++) {
int width, height;
+ u8 cvt_aspect_ratio;

cvt = &(timing->data.other_data.data.cvt[i]);

@@ -3101,7 +3102,8 @@ static int drm_cvt_modes(struct drm_connector *connector,
continue;

height = (cvt->code[0] + ((cvt->code[1] & 0xf0) << 4) + 1) * 2;
- switch (cvt->code[1] & 0x0c) {
+ cvt_aspect_ratio = cvt->code[1] & 0x0c;
+ switch (cvt_aspect_ratio) {
case 0x00:
width = height * 4 / 3;
break;
@@ -3114,6 +3116,8 @@ static int drm_cvt_modes(struct drm_connector *connector,
case 0x0c:
width = height * 15 / 9;
break;
+ default:
+ unreachable();
}

for (j = 1; j < 5; j++) {
--
2.28.0

2020-11-03 22:24:34

by Ilia Mirkin

Subject: Re: [PATCH v2] drm/edid: Fix uninitialized variable in drm_cvt_modes()

On Tue, Nov 3, 2020 at 5:15 PM Lyude Paul <[email protected]> wrote:
>
> Noticed this when trying to compile with -Wall on a kernel fork. We potentially
> don't set width here, which causes the compiler to complain about width
> potentially being uninitialized in drm_cvt_modes(). So, let's fix that.
>
> Changes since v1:
> * Don't emit an error as this code isn't reachable, just mark it as such
>
> Signed-off-by: Lyude Paul <[email protected]>
>
> Cc: <[email protected]> # v5.9+
> Fixes: 3f649ab728cd ("treewide: Remove uninitialized_var() usage")
> Signed-off-by: Lyude Paul <[email protected]>
> ---
> drivers/gpu/drm/drm_edid.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 631125b46e04..0643b98c6383 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -3094,6 +3094,7 @@ static int drm_cvt_modes(struct drm_connector *connector,
>
> for (i = 0; i < 4; i++) {
> int width, height;
> + u8 cvt_aspect_ratio;
>
> cvt = &(timing->data.other_data.data.cvt[i]);
>
> @@ -3101,7 +3102,8 @@ static int drm_cvt_modes(struct drm_connector *connector,
> continue;
>
> height = (cvt->code[0] + ((cvt->code[1] & 0xf0) << 4) + 1) * 2;
> - switch (cvt->code[1] & 0x0c) {
> + cvt_aspect_ratio = cvt->code[1] & 0x0c;

The temp var doesn't do anything now right? Previously you were using
it in the print, but now you can drop these two hunks, I think?

-ilia

> + switch (cvt_aspect_ratio) {
> case 0x00:
> width = height * 4 / 3;
> break;
> @@ -3114,6 +3116,8 @@ static int drm_cvt_modes(struct drm_connector *connector,
> case 0x0c:
> width = height * 15 / 9;
> break;
> + default:
> + unreachable();
> }
>
> for (j = 1; j < 5; j++) {
> --
> 2.28.0
>