Re: ld: error: duplicate symbol:

On 17 Aug 2020, at 15:42, O. Hartmann <ohartmann_at_walstatt.org> wrote:
> 
> On CURRENT 9not necessarily most recent with LLVM11, but since noon of today it
> is FreeBSD 13.0-CURRENT #15 r364297: Mon Aug 17 14:39:06 CEST 2020 amd64) I'm
> faced with some very sticky and nasty micompilations in several essential
> ports, for instance
> 
> ports-mgmt/pkg
> devel/libunwind
> devel/binutils
> 
> In most cases somewhere in the (parallel) build the process fails with the error
> 
> ld: error: duplicate symbol: xxxxxxxx

This is because clang 11 (and gcc 10) now default to -fno-common. The
rationale is explained pretty well in
<https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=6271dd984d7f920d4fb17ad37af6a1f8e6b796dc>:

"GCC currently defaults to -fcommon.  As discussed in the PR, this is an ancient
C feature which is not conforming with the latest C standards.  On many targets
this means global variable accesses have a codesize and performance penalty.
This applies to C code only, C++ code is not affected by -fcommon.  It is about
time to change the default."

A quick fix is to add CFLAGS+=-fcommon to your make.conf, but that is
rather a big hammer. It is better to add it to just the ports that show
problems due to duplicated symbols. And ideally, those duplicated
symbols should be patched out of the ports.

For example, ports-mgmt/pkg already has such a patch:
https://github.com/freebsd/pkg/commit/7fbde60c4af4a1a07db7c5c36efbb2a495f7b1a4
but I have no idea why it is not yet in the ports tree.

-Dimitry