[libcamera-devel] GCC v5,v6 Support and beyond C++14

[Laurent Pinchart]

Hi Kieran,

On Thu, Jul 16, 2020 at 03:12:26PM +0100, Kieran Bingham wrote:
> There has been a few issues lately where we have discussed the minimum
> requirements for libcamera, and we have been supporting from GCC v5
> onwards as much as we can.
> 
> We already depend on features and functionality which is provided in a
> v5.0+ kernel, so that is currently a limiting factor on the low end of
> support.
> 
> If we no longer support GCC v5 and 6, I believe we would also have no
> reason not to move up beyond C++14 to C++17.
> 
> To do so, we need to check that we really don't need to support gcc v5
> or gcc v6 though:
> 
> - Ubuntu only brought in kernel v5.0 at 18.04.3,
>   and 18.04 ships with gcc v7.

Is it as easy to install a custom (backported ?) toolchain on Ubuntu
16.04 (or on other distributions for that matter) that it would be to
install a custom kernel ? Of course "easy" is a subjective concept,
building a kernel is certainly easy for me :-)

Let's also note that, while we require at least a v5.0 kernel, we will
in practice depend on newer kernels for some pipeline handlers. I'm
thinking about vimc in particular, I'm not sure we'll keep support for
older versions once the scaler gets fixed on the kernel side for
instance. I would also not be surprised if we end up depending on fixes
to the IPU3 ImgU driver that are not yet in mainline (because they
haven't been developed yet :-)).

> - On Debian,
>    Stretch(9) uses kernel v4.14,

And ships gcc 6.3.0.

>    Buster(10) has kernel v5.4, and ships with GCC v8.
> 
> - Fedora picks up a v5.0 kernel in Fedora 30, which ships gcc v9.

Should we consider OpenSUSE too ? Gentoo and Arch are certainly not an
issue, and neither are Chrome OS or Android. How about professional
distributions such as RHEL, do we need to care about them ?

> So I don't foresee much reason to keep gcc 5/6 support around ...
> Does anyone know of a distribution that provides a kernel >= 5.0 which
> ships gcc <= 6?

How about buildroot- or yocto-based systems ?

I was hoping kernel v5.0+ would require a newer gcc version, but it
seems it still supports gcc 4.9. No luck there.

-- 
Regards,

Laurent Pinchart