[libcamera-devel] [PATCH 2/2] libcamera: pipeline: simple: Initialize V4L2DeviceFormat before use

[Jacopo Mondi]

Hi Laurent,

On Wed, Oct 21, 2020 at 07:30:53PM +0300, Laurent Pinchart wrote:
> Hi Jacopo,
>
> On Wed, Oct 21, 2020 at 03:13:55PM +0200, Jacopo Mondi wrote:
> > On Wed, Oct 21, 2020 at 05:47:44AM +0300, Laurent Pinchart wrote:
> > > The V4L2DeviceFormat has no default constructor. Zero it before use when
> >
> > Isn't it implicitly generated by the compiler ?
>
> It is, but the implicitly-defined constructor won't help us here:
>
> "If the implicitly-declared default constructor is not defined as
> deleted, it is defined (that is, a function body is generated and
> compiled) by the compiler if odr-used, and it has the same effect as a
> user-defined constructor with empty body and empty initializer list."
>
> (https://en.cppreference.com/w/cpp/language/default_constructor is an
> interesting read)
>

Ah, thanks for the pointer!

> > > setting formats. Failure to do so leaves the planes uninitialized,
> > > potentially causing memory corruption.
> >
> > If not, isn't it better to add it in the class ?
>
> I had considered that, but wasn't sure, and was hoping nobody would ask
> ;-)

I'm sorry :)

But once fixed in the constructor, it's fixed for good, isn't it ?

>
> It could make sense to replace the planes array and planesCount field
> with an std::vector. A bit of a shame to have to use dynamic allocation
> when we know there will never be more than 3 planes though. I wish there
> was a dynamic array container, with fixed memory preallocation and
> dynamic size up to the number of elements.

Can't we use std::array<3> in that case ? Although std::array<> is
horrible to use :(

>
> Any preference between using a vector, and keeping it as-is with a
> constructor that sets numPlanes to 0 ?

To me a constructor sounds quite right, but other options are fine
too.

Thanks
  j

>
> > > Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> > > ---
> > >  src/libcamera/pipeline/simple/converter.cpp | 6 +++---
> > >  1 file changed, 3 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/src/libcamera/pipeline/simple/converter.cpp b/src/libcamera/pipeline/simple/converter.cpp
> > > index b4ee021f6210..b3705abcd626 100644
> > > --- a/src/libcamera/pipeline/simple/converter.cpp
> > > +++ b/src/libcamera/pipeline/simple/converter.cpp
> > > @@ -72,7 +72,7 @@ std::vector<PixelFormat> SimpleConverter::formats(PixelFormat input)
> > >  	 * Set the format on the input side (V4L2 output) of the converter to
> > >  	 * enumerate the conversion capabilities on its output (V4L2 capture).
> > >  	 */
> > > -	V4L2DeviceFormat format;
> > > +	V4L2DeviceFormat format = {};
> > >  	format.fourcc = m2m_->output()->toV4L2PixelFormat(input);
> > >  	format.size = { 1, 1 };
> > >
> > > @@ -103,7 +103,7 @@ SizeRange SimpleConverter::sizes(const Size &input)
> > >  	 * Set the size on the input side (V4L2 output) of the converter to
> > >  	 * enumerate the scaling capabilities on its output (V4L2 capture).
> > >  	 */
> > > -	V4L2DeviceFormat format;
> > > +	V4L2DeviceFormat format = {};
> > >  	format.fourcc = V4L2PixelFormat();
> > >  	format.size = input;
> > >
> > > @@ -142,7 +142,7 @@ SizeRange SimpleConverter::sizes(const Size &input)
> > >  int SimpleConverter::configure(PixelFormat inputFormat, const Size &inputSize,
> > >  			       StreamConfiguration *cfg)
> > >  {
> > > -	V4L2DeviceFormat format;
> > > +	V4L2DeviceFormat format = {};
> > >  	int ret;
> > >
> > >  	V4L2PixelFormat videoFormat = m2m_->output()->toV4L2PixelFormat(inputFormat);
>
> --
> Regards,
>
> Laurent Pinchart