[2.6.37-rc7] drivers/gpu/drm/drm_edid.c:1303: warning: array subscript is above array bounds

[2.6.37-rc7] drivers/gpu/drm/drm_edid.c:1303: warning: array subscript is above array bounds

[Jarek Poplawski]

Hi,
There is this compile warning in Linus' tree (gcc version 4.3.3):

drivers/gpu/drm/drm_edid.c: In function 'drm_detect_hdmi_monitor':
drivers/gpu/drm/drm_edid.c:1303: warning: array subscript is above array bounds
drivers/gpu/drm/drm_edid.c: In function 'drm_detect_monitor_audio':
drivers/gpu/drm/drm_edid.c:1303: warning: array subscript is above array bounds

Cheers,
Jarek P.

Re: [2.6.37-rc7] drivers/gpu/drm/drm_edid.c:1303: warning: array subscript is above array bounds

[Chris Wilson]

On Sat, 25 Dec 2010 14:13:43 +0100, Jarek Poplawski <jarkao2@gmail.com> wrote:
> Hi,
> There is this compile warning in Linus' tree (gcc version 4.3.3):
> 
> drivers/gpu/drm/drm_edid.c: In function 'drm_detect_hdmi_monitor':
> drivers/gpu/drm/drm_edid.c:1303: warning: array subscript is above array bounds
> drivers/gpu/drm/drm_edid.c: In function 'drm_detect_monitor_audio':
> drivers/gpu/drm/drm_edid.c:1303: warning: array subscript is above array bounds

What array? It's declared as "u8 *edid_ext;". At first glance looks like a
compiler bug, applying subscript testing to an object with unknown bounds.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre

Re: [2.6.37-rc7] drivers/gpu/drm/drm_edid.c:1303: warning: array subscript is above array bounds

[Jarek Poplawski]

On Sat, Dec 25, 2010 at 01:38:56PM +0000, Chris Wilson wrote:
> On Sat, 25 Dec 2010 14:13:43 +0100, Jarek Poplawski <jarkao2@gmail.com> wrote:
> > Hi,
> > There is this compile warning in Linus' tree (gcc version 4.3.3):
> > 
> > drivers/gpu/drm/drm_edid.c: In function 'drm_detect_hdmi_monitor':
> > drivers/gpu/drm/drm_edid.c:1303: warning: array subscript is above array bounds
> > drivers/gpu/drm/drm_edid.c: In function 'drm_detect_monitor_audio':
> > drivers/gpu/drm/drm_edid.c:1303: warning: array subscript is above array bounds
> 
> What array? It's declared as "u8 *edid_ext;". At first glance looks like a
> compiler bug, applying subscript testing to an object with unknown bounds.

Maybe a bug but then also something very unique in this place wrt the
rest of the kernel (at least in my config). Btw, a patch below removes
this warning.

Jarek P.

--- drm_edid.c-	2010-12-25 19:24:55.000000000 +0100
+++ drm_edid.c	2010-12-25 19:51:45.000000000 +0100
@@ -1290,7 +1290,7 @@ add_detailed_modes(struct drm_connector 
  */
 static u8 *drm_find_cea_extension(struct edid *edid)
 {
-	u8 *edid_ext = NULL;
+	char *edid_ext = NULL;
 	int i;
 
 	/* No EDID or EDID extensions */
@@ -1299,7 +1299,7 @@ static u8 *drm_find_cea_extension(struct
 
 	/* Find CEA extension */
 	for (i = 0; i < edid->extensions; i++) {
-		edid_ext = (u8 *)edid + EDID_LENGTH * (i + 1);
+		edid_ext = (char *)edid + EDID_LENGTH * (i + 1);
 		if (edid_ext[0] == CEA_EXT)
 			break;
 	}