Re: [PATCH] drm/edid: Distribute switch variables for initialization

Re: [PATCH] drm/edid: Distribute switch variables for initialization

[Kees Cook]

On Wed, Feb 19, 2020 at 10:22:29PM -0800, Kees Cook wrote:
> Variables declared in a switch statement before any case statements
> cannot be automatically initialized with compiler instrumentation (as
> they are not part of any execution flow). With GCC's proposed automatic
> stack variable initialization feature, this triggers a warning (and they
> don't get initialized). Clang's automatic stack variable initialization
> (via CONFIG_INIT_STACK_ALL=y) doesn't throw a warning, but it also
> doesn't initialize such variables[1]. Note that these warnings (or silent
> skipping) happen before the dead-store elimination optimization phase,
> so even when the automatic initializations are later elided in favor of
> direct initializations, the warnings remain.
> 
> To avoid these problems, move such variables into the "case" where
> they're used or lift them up into the main function body.
> 
> drivers/gpu/drm/drm_edid.c: In function ‘drm_edid_to_eld’:
> drivers/gpu/drm/drm_edid.c:4395:9: warning: statement will never be executed [-Wswitch-unreachable]
>  4395 |     int sad_count;
>       |         ^~~~~~~~~
> 
> [1] https://bugs.llvm.org/show_bug.cgi?id=44916
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>

Ping. Can someone pick this up, please?

Thanks!

-Kees

> ---
>  drivers/gpu/drm/drm_edid.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 805fb004c8eb..2941b65b427f 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -4392,9 +4392,9 @@ static void drm_edid_to_eld(struct drm_connector *connector, struct edid *edid)
>  			dbl = cea_db_payload_len(db);
>  
>  			switch (cea_db_tag(db)) {
> -				int sad_count;
> +			case AUDIO_BLOCK: {
>  
> -			case AUDIO_BLOCK:
> +				int sad_count;
>  				/* Audio Data Block, contains SADs */
>  				sad_count = min(dbl / 3, 15 - total_sad_count);
>  				if (sad_count >= 1)
> @@ -4402,6 +4402,7 @@ static void drm_edid_to_eld(struct drm_connector *connector, struct edid *edid)
>  					       &db[1], sad_count * 3);
>  				total_sad_count += sad_count;
>  				break;
> +			}
>  			case SPEAKER_BLOCK:
>  				/* Speaker Allocation Data Block */
>  				if (dbl >= 1)
> 

-- 
Kees Cook
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

Re: [PATCH] drm/edid: Distribute switch variables for initialization

[Daniel Vetter]

On Tue, Mar 3, 2020 at 5:39 AM Kees Cook <keescook@chromium.org> wrote:
>
> On Wed, Feb 19, 2020 at 10:22:29PM -0800, Kees Cook wrote:
> > Variables declared in a switch statement before any case statements
> > cannot be automatically initialized with compiler instrumentation (as
> > they are not part of any execution flow). With GCC's proposed automatic
> > stack variable initialization feature, this triggers a warning (and they
> > don't get initialized). Clang's automatic stack variable initialization
> > (via CONFIG_INIT_STACK_ALL=y) doesn't throw a warning, but it also
> > doesn't initialize such variables[1]. Note that these warnings (or silent
> > skipping) happen before the dead-store elimination optimization phase,
> > so even when the automatic initializations are later elided in favor of
> > direct initializations, the warnings remain.
> >
> > To avoid these problems, move such variables into the "case" where
> > they're used or lift them up into the main function body.
> >
> > drivers/gpu/drm/drm_edid.c: In function ‘drm_edid_to_eld’:
> > drivers/gpu/drm/drm_edid.c:4395:9: warning: statement will never be executed [-Wswitch-unreachable]
> >  4395 |     int sad_count;
> >       |         ^~~~~~~~~
> >
> > [1] https://bugs.llvm.org/show_bug.cgi?id=44916
> >
> > Signed-off-by: Kees Cook <keescook@chromium.org>
>
> Ping. Can someone pick this up, please?

Whatever the reasons, but your original patch didn't make it through
to dri-devel. Can you pls resubmit?

Thanks, Daniel

>
> Thanks!
>
> -Kees
>
> > ---
> >  drivers/gpu/drm/drm_edid.c |    5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> > index 805fb004c8eb..2941b65b427f 100644
> > --- a/drivers/gpu/drm/drm_edid.c
> > +++ b/drivers/gpu/drm/drm_edid.c
> > @@ -4392,9 +4392,9 @@ static void drm_edid_to_eld(struct drm_connector *connector, struct edid *edid)
> >                       dbl = cea_db_payload_len(db);
> >
> >                       switch (cea_db_tag(db)) {
> > -                             int sad_count;
> > +                     case AUDIO_BLOCK: {
> >
> > -                     case AUDIO_BLOCK:
> > +                             int sad_count;
> >                               /* Audio Data Block, contains SADs */
> >                               sad_count = min(dbl / 3, 15 - total_sad_count);
> >                               if (sad_count >= 1)
> > @@ -4402,6 +4402,7 @@ static void drm_edid_to_eld(struct drm_connector *connector, struct edid *edid)
> >                                              &db[1], sad_count * 3);
> >                               total_sad_count += sad_count;
> >                               break;
> > +                     }
> >                       case SPEAKER_BLOCK:
> >                               /* Speaker Allocation Data Block */
> >                               if (dbl >= 1)
> >
>
> --
> Kees Cook



-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

Re: [PATCH] drm/edid: Distribute switch variables for initialization

[Ville Syrjälä]

On Mon, Mar 02, 2020 at 08:39:37PM -0800, Kees Cook wrote:
> On Wed, Feb 19, 2020 at 10:22:29PM -0800, Kees Cook wrote:
> > Variables declared in a switch statement before any case statements
> > cannot be automatically initialized with compiler instrumentation (as
> > they are not part of any execution flow). With GCC's proposed automatic
> > stack variable initialization feature, this triggers a warning (and they
> > don't get initialized). Clang's automatic stack variable initialization
> > (via CONFIG_INIT_STACK_ALL=y) doesn't throw a warning, but it also
> > doesn't initialize such variables[1]. Note that these warnings (or silent
> > skipping) happen before the dead-store elimination optimization phase,
> > so even when the automatic initializations are later elided in favor of
> > direct initializations, the warnings remain.
> > 
> > To avoid these problems, move such variables into the "case" where
> > they're used or lift them up into the main function body.
> > 
> > drivers/gpu/drm/drm_edid.c: In function ‘drm_edid_to_eld’:
> > drivers/gpu/drm/drm_edid.c:4395:9: warning: statement will never be executed [-Wswitch-unreachable]
> >  4395 |     int sad_count;
> >       |         ^~~~~~~~~
> > 
> > [1] https://bugs.llvm.org/show_bug.cgi?id=44916
> > 
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> 
> Ping. Can someone pick this up, please?
> 
> Thanks!
> 
> -Kees
> 
> > ---
> >  drivers/gpu/drm/drm_edid.c |    5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> > index 805fb004c8eb..2941b65b427f 100644
> > --- a/drivers/gpu/drm/drm_edid.c
> > +++ b/drivers/gpu/drm/drm_edid.c
> > @@ -4392,9 +4392,9 @@ static void drm_edid_to_eld(struct drm_connector *connector, struct edid *edid)
> >  			dbl = cea_db_payload_len(db);
> >  
> >  			switch (cea_db_tag(db)) {
> > -				int sad_count;
> > +			case AUDIO_BLOCK: {

I've never been a fan of {} inside switch statements. I'd just
move this one level up.

> >  
> > -			case AUDIO_BLOCK:
> > +				int sad_count;
> >  				/* Audio Data Block, contains SADs */
> >  				sad_count = min(dbl / 3, 15 - total_sad_count);
> >  				if (sad_count >= 1)
> > @@ -4402,6 +4402,7 @@ static void drm_edid_to_eld(struct drm_connector *connector, struct edid *edid)
> >  					       &db[1], sad_count * 3);
> >  				total_sad_count += sad_count;
> >  				break;
> > +			}
> >  			case SPEAKER_BLOCK:
> >  				/* Speaker Allocation Data Block */
> >  				if (dbl >= 1)
> > 
> 
> -- 
> Kees Cook
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Ville Syrjälä
Intel
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel