[libcamera-devel] [PATCH] libcamera: v4l2_device: Fix variable-sized object initialization

[Laurent Pinchart]

Hi Jacopo,

On Fri, Jun 28, 2019 at 08:07:48AM +0200, Jacopo Mondi wrote:
> Hi Niklas,
>    sorry, I didn't test on clang. It should become a standard practice
> since it's the default compiler used for building, ie, Cros..
> 
> On Wed, Jun 26, 2019 at 07:35:43PM +0200, Nklas Söderlund wrote:
> > Compiling with clang renders errors as a variable-sized arrays are not
> > allowed to be initialized, solve this by using memset() instead.
> >
> >     ../../src/libcamera/v4l2_device.cpp:155:37: error: variable-sized object may not be initialized
> >         const V4L2ControlInfo *controlInfo[count] = {};
> >                                            ^~~~~
> >     ../../src/libcamera/v4l2_device.cpp:156:36: error: variable-sized object may not be initialized
> > 	    struct v4l2_ext_control v4l2Ctrls[count] = {};
> > 					      ^~~~~
> >     ../../src/libcamera/v4l2_device.cpp:227:37: error: variable-sized object may not be initialized
> > 	    const V4L2ControlInfo *controlInfo[count] = {};
> > 					       ^~~~~
> >     ../../src/libcamera/v4l2_device.cpp:228:36: error: variable-sized object may not be initialized
> > 	    struct v4l2_ext_control v4l2Ctrls[count] = {};
> > 					      ^~~~~
> > Fixes: eb068f4e67eedacd ("libcamera: v4l2_device: Implement get and set controls")
> > Signed-off-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>
> > ---
> >  src/libcamera/v4l2_device.cpp | 13 +++++++++----
> >  1 file changed, 9 insertions(+), 4 deletions(-)
> >
> > diff --git a/src/libcamera/v4l2_device.cpp b/src/libcamera/v4l2_device.cpp
> > index 84758a811c271976..d730df78e1ab2478 100644
> > --- a/src/libcamera/v4l2_device.cpp
> > +++ b/src/libcamera/v4l2_device.cpp
> > @@ -152,8 +152,11 @@ int V4L2Device::getControls(V4L2ControlList *ctrls)
> >  	if (count == 0)
> >  		return 0;
> >
> > -	const V4L2ControlInfo *controlInfo[count] = {};
> > -	struct v4l2_ext_control v4l2Ctrls[count] = {};
> > +	const V4L2ControlInfo *controlInfo[count];
> 
> No need to zero this one.
> 
> > +	struct v4l2_ext_control v4l2Ctrls[count];
> 
> We can initialize each entry as we walk them maybe?
> 
> --- a/src/libcamera/v4l2_device.cpp
> +++ b/src/libcamera/v4l2_device.cpp
> @@ -152,8 +152,8 @@ int V4L2Device::getControls(V4L2ControlList *ctrls)
>         if (count == 0)
>                 return 0;
> 
> -       const V4L2ControlInfo *controlInfo[count] = {};
> -       struct v4l2_ext_control v4l2Ctrls[count] = {};
> +       const V4L2ControlInfo *controlInfo[count];
> +       struct v4l2_ext_control v4l2Ctrls[count];
>         for (unsigned int i = 0; i < count; ++i) {
>                 const V4L2Control *ctrl = ctrls->getByIndex(i);
>                 const V4L2ControlInfo *info = getControlInfo(ctrl->id());
> @@ -164,6 +164,7 @@ int V4L2Device::getControls(V4L2ControlList *ctrls)
>                 }
> 
>                 controlInfo[i] = info;
> +               v4l2Ctrls[i] = {};
>                 v4l2Ctrls[i].id = info->id();
>         }
> With the same to be done for setControl()?
> 
> What do you think?

Wouldn't a single memset be more efficient ?

> > +	memset(controlInfo, 0, count * sizeof(controlInfo[0]));
> > +	memset(v4l2Ctrls, 0, count * sizeof(v4l2Ctrls[0]));
> > +
> >  	for (unsigned int i = 0; i < count; ++i) {
> >  		const V4L2Control *ctrl = ctrls->getByIndex(i);
> >  		const V4L2ControlInfo *info = getControlInfo(ctrl->id());
> > @@ -224,8 +227,10 @@ int V4L2Device::setControls(V4L2ControlList *ctrls)
> >  	if (count == 0)
> >  		return 0;
> >
> > -	const V4L2ControlInfo *controlInfo[count] = {};
> > -	struct v4l2_ext_control v4l2Ctrls[count] = {};
> > +	const V4L2ControlInfo *controlInfo[count];
> > +	struct v4l2_ext_control v4l2Ctrls[count];
> > +	memset(controlInfo, 0, count * sizeof(controlInfo[0]));
> > +	memset(v4l2Ctrls, 0, count * sizeof(v4l2Ctrls[0]));
> >
> >  	for (unsigned int i = 0; i < count; ++i) {
> >  		const V4L2Control *ctrl = ctrls->getByIndex(i);

-- 
Regards,

Laurent Pinchart