linker fails with multiple definitions after inline thread_local var within class

[Brian Inglis]

On 2019-11-15 20:35, Brian Inglis wrote:
> On 2019-11-15 15:25, Arthur Norman wrote:
>>> I notice that you are not independently compiling your source files and have no
>>> include guard in t.h.
>>> Could I suggest that you add the include guard to t.h and retest.
>>> If you still have an issue, try independently compiling your source files, then
>>> linking them as a separate step, to see if that works.
>>> You could also test reproducing the issue on another gcc platform, under a Unix
>>> VM, or a WSL Linux distro.
>>
>> I attach a versiuon of the test with an include guard and with t1.cpp and t2.cpp
>> compiled in separate invocations of g++ - I still see the multiple definition.
>>
>> ${1:-g++} -std=c++17 -I. -c t1.cpp
>> ${1:-g++} -std=c++17 -I. -c t2.cpp
>> ${1:-g++} -std=c++17 t1.o t2.o -o t
>> /usr/lib/gcc/x86_64-pc-cygwin/8.3.0/../../../../x86_64-pc-cygwin/bin/ld:
>> t2.o:t2.cpp:(.text+0x86): multiple definition of `TLS init function for
>> Data::valref'; t1.o:t1.cpp:(.text+0x4a): first defined here
>> collect2: error: ld returned 1 exit status
>> ./t
>>
>> As per my original posting before enquiring here I had tried on a 64-bit ubuntu
>> machine, on a Macbook (where it is clang not g++, but I invoke the compiler as
>> g++) and on a Raspberry pi.
> 
> Sorry missed that.
> 
>> The original code I had pain with was with include guards and all files compiled
>> independently via make - the test casee I submitted had perhaps tried to hard to
>> shorten and simplify.
>>
>> I also tried both 32 and 64-bit mingw compilers under cygwin - making that
>> easier is why the test script goes ${1:-g++} so I can override the compiler
>> selection to be x86_64-w64-mingw32-g++ or the i686 variant. Those both show the
>> multiple definition problem.
> 
> That points to a common problem with the loader generating Windows PEs: it is
> possible that is a Windows limitation.
> As ld is part of binutils, you might want to try searching and posting on that
> mailing list, conveniently located just next door:
> 
> 	https://sourceware.org/binutils/
> 	http://sourceware.org/ml/binutils/
> 	http://lists.gnu.org/archive/html/bug-binutils/
> 
> before looking further at gcc.

OTOH:	https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64697#c20

> Please emphasize clearly that this works successfully with ELF executables on
> Unix platforms, and list those; and ld fails only with Windows (PE) executables
> using Cygwin and Mingw 32/64 tool chains, and list those; and include the test
> code, commands and results on each platform, to clearly demonstrate the issue.
> Use a specific subject to get appropriate attention and a relevant response e.g.
> "ld fails only for Windows PE with multiple definition of TLS init function".

-- 
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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