[libcamera-devel] [PATCH v3] cam: file_sink: Fixes following errors with gcc-13

[Laurent Pinchart]

On Tue, Mar 28, 2023 at 10:26:58AM -0700, Khem Raj wrote:
> On Tue, Mar 28, 2023 at 10:13 AM Kieran Bingham wrote:
> > Quoting Eric Curtin (2023-02-20 04:55:24)
> > > ../git/src/cam/file_sink.cpp:92:45: error: possibly dangling reference to a temporary [-Werror=dangling-reference]
> > >    92 |                 const FrameMetadata::Plane &meta = buffer->metadata().planes()[i];
> > >       |                                             ^~~~
> > > ../git/src/cam/file_sink.cpp:92:81: note: the temporary was destroyed at the end of the full expression '(& buffer->libcamera::FrameBuffer::metadata())->libcamera::FrameMetadata::planes().libcamera::Span<const libcamera::FrameMetadata::Plane>::operator[](i)'
> > >    92 |                 const FrameMetadata::Plane &meta = buffer->metadata().planes()[i];
> > >       |                                                                                 ^
> > > cc1plus: all warnings being treated as errors
> > >
> > > Co-developed-by: Khem Raj <raj.khem at gmail.com>
> > > Signed-off-by: Eric Curtin <ecurtin at redhat.com>
> >
> > I'm still hoping that holding off a little on this will ensure it's
> > fixed in the compiler before GCC-13 is released - but I think I can also
> > already add:
> >
> > Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> >
> > And given a fix was added to gcc-13, but it didn't fix /this/ we may be
> > getting to the point that we'll simply have to merge this. I guess it
> > depends on when gcc-13 is actually released?
> 
> In a months time. It perhaps is not going to be fixed by atleast the
> first 13.x release. Maybe subsequent point releases
> might have it

It looks like this won't be fixed in gcc :-(

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108165#c9

Their recommendation is to use a pragma to disable the warning:

diff --git a/src/apps/cam/file_sink.cpp b/src/apps/cam/file_sink.cpp
index b32aad247b8b..5fb075261a18 100644
--- a/src/apps/cam/file_sink.cpp
+++ b/src/apps/cam/file_sink.cpp
@@ -114,7 +114,10 @@ void FileSink::writeBuffer(const Stream *stream, FrameBuffer *buffer,
 	}

 	for (unsigned int i = 0; i < buffer->planes().size(); ++i) {
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wdangling-reference"
 		const FrameMetadata::Plane &meta = buffer->metadata().planes()[i];
+#pragma GCC diagnostic pop

 		Span<uint8_t> data = image->data(i);
 		unsigned int length = std::min<unsigned int>(meta.bytesused, data.size());

> > > ---
> > > Changes in v3:
> > >
> > > - Added comment explaining change made because of false negative in gcc
> > >
> > > Changes in v2:
> > >
> > > - Added const
> > > - Made patch mergeable by accounting for new directory structure
> > > ---
> > >  src/apps/cam/file_sink.cpp | 14 +++++++++-----
> > >  1 file changed, 9 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/src/apps/cam/file_sink.cpp b/src/apps/cam/file_sink.cpp
> > > index b32aad24..01846cdb 100644
> > > --- a/src/apps/cam/file_sink.cpp
> > > +++ b/src/apps/cam/file_sink.cpp
> > > @@ -114,13 +114,17 @@ void FileSink::writeBuffer(const Stream *stream, FrameBuffer *buffer,
> > >         }
> > >
> > >         for (unsigned int i = 0; i < buffer->planes().size(); ++i) {
> > > -               const FrameMetadata::Plane &meta = buffer->metadata().planes()[i];
> > > -
> > > +               /*
> > > +                * formerly "const FrameMetadata::Plane &"
> > > +                * causing false negative (gcc 13):
> > > +                * "possibly dangling reference to a temporary"
> > > +                */
> > > +               const unsigned int bytesused = buffer->metadata().planes()[i].bytesused;
> > >                 Span<uint8_t> data = image->data(i);
> > > -               unsigned int length = std::min<unsigned int>(meta.bytesused, data.size());
> > > +               const unsigned int length = std::min<unsigned int>(bytesused, data.size());
> > >
> > > -               if (meta.bytesused > data.size())
> > > -                       std::cerr << "payload size " << meta.bytesused
> > > +               if (bytesused > data.size())
> > > +                       std::cerr << "payload size " << bytesused
> > >                                   << " larger than plane size " << data.size()
> > >                                   << std::endl;
> > >

-- 
Regards,

Laurent Pinchart