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

[Laurent Pinchart]

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)

> > 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
;-)

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.

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

> > 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