[oe] [meta-java][PATCH] openjdk-8: make GCC6 happy

[Patrick Ohly]

Dan McGregor <danismostlikely <at> gmail.com> writes: 
> On 11 July 2016 at 05:29, Patrick Ohly <patrick.ohly <at> intel.com> wrote:
> > Dan McGregor <danismostlikely <at> gmail.com> writes:
> >> From: Daniel McGregor <daniel.mcgregor <at> vecima.com>
> >>
> >> GCC 6 sets the default C++ standard to C++14 and introduces dead store
> >> elimination by default. OpenJDK 8 is not ready for either of these
> >> changes, so set the C++ standard back to gnu++98 and disable dead
> >> store elimination.
> >>
> >> Switched to using --with-extra-cflags, cxxflags, and ldflags. The added
> >> patch fixes building when using those flags, and are needed to get
> >> CFLAGS into the JDK build in the native case.
> >
> > Has anyone tested this on a host system where gcc is still 4.x, like 4.9.2
> > on Debian Wheezy?
> >
> > I'm finding that -fno-lifetime-dse is also getting passed to the gcc used
> > for compiling native binaries (obviously in openjdk-8-native, but also for
> > some helper executables in openjdk-8). This then breaks the compilation
> > because older gcc rejects that flag.
> >
> > I've briefly toyed with the patch below which worked for openjdk-8-native,
> > but not for openjdk-8. I'm just going to work around it by staying on gcc
> > 5.x and clearing these extra flags.
> >
> > I'm not familiar enough with the openjdk-8 build process to propose a better
> > solution, but perhaps someone else has an idea?
> >
[...]
> This regex doesn't work in the cross case because the version string
> doesn't start with "gcc". It starts with '<target-triple>-gcc', so
> that should be checked instead.
> 
> I'll fiddle with this patch some more. It looks like a good short-term
> solution to building OpenJDK on GCC 4 hosts.

Thanks for taking this further. But please really test on such an older 
system, because the patch alone is not enough. Something also needs to
be done when configuring openjdk-8 such that it uses different flags
when invoking the host compiler (old gcc) and the target compiler (gcc 6).

I haven't found a solution for that (not familiar enough with the Java
build system).

Bye, Patrick