Switch to gcc 6.3 as minimum requirement?

[doe300]

Currently, VC4C and VC4CL are held compatible with the ancient GCC 4.8 to support older Raspbian systems. GCC 4.8 barely supports C++11 [1] and hence lacks a lot of useful new features provided in C++14 and C++17. The latest Raspian Stretch ships with GCC 6.3, which completely supports C++14 as well as a lot of C++17 features [1].

Some useful C++14/C++17 features we could use when switching [1]:

• Full support for variadic templates
• Extended constexpr functions
• __has_include e.g. for distinguishing LLVM versions
• New library features: string_view, file-system support, optional and any in experimental namespace

Since the official raspberrypi-tools repository has not yet been upgraded to GCC 6.3 (see here), we would need to use another tool-chain for our CircleCI cross-compilation such as this one (see also here).

So the question is:
Should we drop support for GCC 4.8 and therefore for older Raspbian systems?

[1] https://gcc.gnu.org/projects/cxx-status.html

[fighne]

I think the ease of access to the Raspbian image, and the supported hardware ( I have an original Raspberry Pi which it runs on ) I personally think it's a yes.

[doe300]

Just a quick questions to anyone who has more experience with gcc-versions and targets than I have.
For the CircleCI build, can't we just switch to g++-arm-linux-gnueabihf as cross-compiler? Or do we have to use a custom-build compiler for the raspberry pi (as idein does)? If so, why?
@nomaddo, any ideas?

[nomaddo]

@doe300
Why we use custom-build compiler is that, other choices has cons as following:

• linaro cross compilers: armv6 compiler lacks support for hardfp
• g++-arm-linux-gnueabihf: it lacks support for NEON

In this case, we care support for march armv6 and armv7 with hardfp, not care for NEON acceleration.
with g++-arm-linux-gnueabihf in Debian:stretch, solving dependent libraries may be easier.
OK, I will create new Dockerfile.

[Terminus-IMRC]

My cross-rpi repo is obsolete, so please use our new one: https://github.com/Idein/docker-cross-rpi

[Terminus-IMRC]

@nomaddo linaro's arm toolchain lacks support for armv6 itself, not vfp...

[nomaddo]

@Terminus-IMRC very thanks for the correction :)

[Terminus-IMRC]

After some investigations, it turned out that cross toolchain of Linaro and Debian both support armv6 (VFP) and armv7 (NEON), which means that you can just switch to use g++-arm-linux-gnueabihf as cross compiler. Sorry for misleading comments.