Tuesday, 13 May 2014

preparing for GCC 4.9

[[ sent the appended email to debian-devel. I'm planning to do the default
change around the same time for utopic. Build failures are not filed
in Ubuntu, please use [3] for now. When fixing an issue ahead of Debian
please make sure to attach the patch to the Debian issue. And please
join the bug squashing on Fri/Sat (we'll be on #ubuntu-devel as well).

Use the ubuntu-toolchain-r/test PPA [7] to set gcc to gcc-4.9.

With gcc-4.9 now available in testing, it is time to prepare for the change of
the default to 4.9, for a subset of architectures or for all (release)
architectures. The defaults for the gdc, gccgo, gcj and gnat frontends already
point to 4.9 and are used on all architectures. Issue #746805 tracks the
gfortran default change, including the change of the Fortran 90 module version.

An email a week ago to debian-{release,ports} [1] didn't show any obvious
blockers, and various test rebuilds don't show at least any internal compiler
errors anymore.

The Debian archive was rebuilt twice on amd64, once in February, resulting in
bug submissions for GCC and feedback for the porting guide [2], a second time in
March to file issues for packages failing to build with GCC 4.9 [3]. Another
test rebuild for mips64 didn't show any additional build failures [4]. Another
test rebuild for Ubuntu on amd64, i386, armhf, ppc64el didn't show any other
compiler regressions on these architectures.

I'll work on fixing the build failures in [3], help is of course appreciated.
Trying to be online on May 16/17 on IRC #debian-toolchain (OFTC) and uploading
packages to the delayed queue.

Almost all build failures are analysed and should be easy to fix (exceptions
e.g. #746883). Patches for the ones not caused by the Debian packaging may be
found in distributions already using GCC 4.9 as the default compiler (e.g.
Fedora 21).

If anything goes well, and a large amount of build failures are fixed, I plan to
make GCC 4.9 the default for the C/C++/ObjC/Obj-C++ frontends at the end of May,
beginning of June.

Bugs reports for packages building with a legacy version of GCC (4.6, 4.7) are
filed [5] [6], and will be filed for 4.8 once 4.9 is the default.


[1] https://lists.debian.org/debian-release/2014/05/msg00086.html
[2] http://gcc.gnu.org/gcc-4.9/porting_to.html
[4] https://lists.debian.org/debian-release/2014/05/msg00087.html
[7] deb http://ppa.launchpad.net/ubuntu-toolchain-r/test/ubuntu utopic main

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