GCC 7.3.0 fails to build on CentOS 6.x

[migueldiascosta]

as also seen with 8.1.0 on #6296, the solution there was to add GCC 6.4.0 as builddependency

(the issue seems to be with mpfr 4.x, where Link Time Optimization is enabled by default but not supported by the system GCC in CentOS 6.x, so an alternative solution could patch mpfr to disable LTO on CentOS 6.x)

[boegel]

I'm more in favor of adding GCCcore 6.4.0 as a build dependency for GCCcore 7.3.0, like we did for GCCcore 8.1.0, but I'd like to get some feedback from others on this...

It's important to get this right, since GCC 7.3 is likely to be the base for the 2018b toolchain (I got feedback from Intel support that they are not aware of any big issues when using it with Intel compilers 2018 update 2, i.e. latest).

@geimer, @wpoely86, @akesandgren: thoughts?

[akesandgren]

I would make that a site dep only. CentOS 6 should've been scrapped long ago.

[boegel]

@akesandgren It seems CentOS 6 is still used at various sites, so I think we should do a minimal amount of effort to keep supporting it (at least in EasyBuild v3.x).

If we do include GGCcore 6.4.0 as a build dep for GCCcore 7.3.0 (like we already do for GCCcore 8.1.0 to be included with EasyBuild v3.6.1), we may need to find a way to break that cycle though, we don't want to have a whole stack of GCC installations to compile to get to the GCC we actually want...

[geimer]

@boegel Fixing CentOS 6 may break things on recent Ubuntu's (and maybe other distros as well), as GCC 6.4.0 won't build with glibc 2.26... See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81712

[boegel]

Hmm, I wonder why nobody has brought that up yet... Can somebody test that? @akesandgren, @vanzod?

If so, that's certainly a problem, and a reason to consider making the use of a recent GCC conditional to only CentOS 6 somehow...

[akesandgren]

Why are you talking about 2.26 for GCC 6.4.0?? EB uses 2.28 for GCC-6.4.0...eb

[bartoldeman]

binutils-2.28, not glibc-2.26 :)

maybe just apply the upstream patch to GCCcore 6.4.0?

[akesandgren]

Ooops, shouldn't read and reply when brain is otherwise engaged...

[vanzod]

I do not like much the solution of adding GCCcore/6.4.0 as default dependency. Having it optional for CentOS 6 users seem a cleaner way to me. If a comment in the easyconfig file may be ignored by users, how about adding a system GCC version check in the easyblock and automatically add the GCCcore/6.4.0 dependency if the version is too old?

[boegel]

One other option, mentioned by @bartoldeman during today's conf call is to build MPFR without -lto in stage 1, by modifying the GCC easyblock.

This is the best option imho, since:

• i) we can do it dynamically (i.e. only when we notice that the gcc version is too old),
• ii) it doesn't affect the final result of the GCC installation because of the staged build

I'll take a stab at that...

[boegel]

see easybuilders/easybuild-easyblocks#1435