On Tue, Nov 3, 2020 at 2:47 PM Lyude Paul <lyude@xxxxxxxxxx> wrote: > > Sorry! Thought I had responded to this but apparently not, comments down below > > On Thu, 2020-10-22 at 14:04 -0400, Ilia Mirkin wrote: > > On Thu, Oct 22, 2020 at 12:55 PM Lyude Paul <lyude@xxxxxxxxxx> 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. > > > > > > Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx> > > > > > > Cc: <stable@xxxxxxxxxxxxxxx> # v5.9+ > > > Fixes: 3f649ab728cd ("treewide: Remove uninitialized_var() usage") > > > Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx> > > > --- > > > drivers/gpu/drm/drm_edid.c | 8 +++++++- > > > 1 file changed, 7 insertions(+), 1 deletion(-) > > > > > > diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c > > > index 631125b46e04..2da158ffed8e 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 +3116,10 @@ static int drm_cvt_modes(struct drm_connector > > > *connector, > > > case 0x0c: > > > width = height * 15 / 9; > > > break; > > > + default: > > > > What value would cvt->code[1] have such that this gets hit? > > > > Or is this a "compiler is broken, so let's add more code" situation? > > If so, perhaps the code added could just be enough to silence the > > compiler (unreachable, etc)? > > I mean, this information comes from the EDID which inherently means it's coming > from an untrusted source so the value could be literally anything as long as the > EDID has a valid checksum. Note (assuming I'm understanding this code > correctly): > > drm_add_edid_modes() → add_cvt_modes() → drm_for_each_detailed_block() → > do_cvt_mode() → drm_cvt_modes() > > So afaict this isn't a broken compiler but a legitimate uninitialized variable. The value can be anything, but it has to be something. The switch is on "unknown & 0x0c", so only 4 cases are possible, which are enumerated in the switch. -ilia _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel