[llvm-dev] Linker failures in debug build - compiler/linker poll?

[Mehdi Amini via llvm-dev]

Hi,


> On Jun 18, 2016, at 4:34 AM, Nicolai Hähnle via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> Hi,
> 
> since recently I'm getting linker failures in debug builds. The root cause is that -fvisibility-inlines-hidden causes inline functions in explicit template instantiations to become hidden in certain cases.

I’m not sure I understand how it can be a link failure right now.

A minimal test case would be nice.

Thanks,

— 
Mehdi



> 
> The following hunk works around this...
> 
> --- a/cmake/modules/HandleLLVMOptions.cmake
> +++ b/cmake/modules/HandleLLVMOptions.cmake
> @@ -159,7 +159,13 @@ endif()
> if(NOT WIN32 AND NOT CYGWIN)
>  # MinGW warns if -fvisibility-inlines-hidden is used.
>  check_cxx_compiler_flag("-fvisibility-inlines-hidden" SUPPORTS_FVISIBILITY_INLINES_HIDDEN_FLAG)
> -  append_if(SUPPORTS_FVISIBILITY_INLINES_HIDDEN_FLAG "-fvisibility-inlines-hidden" CMAKE_CXX_FLAGS)
> +
> +  # The flag also hides inlines from explicit template instantiations, which
> +  # leads to link failures in debug builds at least with gcc 5.3.1 and
> +  # both GNU ld 2.26 or gold 1.11.
> +  if (NOT uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG")
> +    append_if(SUPPORTS_FVISIBILITY_INLINES_HIDDEN_FLAG "-fvisibility-inlines-hidden" CMAKE_CXX_FLAGS)
> +  endif()
> endif()
> 
> if( CMAKE_SIZEOF_VOID_P EQUAL 8 AND NOT WIN32 )
> 
> ... but before I just wildly commit something, I'd say this does seem more like a compiler bug to me and so I'd like to poll people about which compilers they're using to see where this appears.
> 
> FWIW, gcc 5.3.1 / ld 2.26 / gold 1.11 is what you get in Ubuntu 16.04.
> 
> Also note: This has surfaced only recently, because of how the symbol types evolve during the different linker stages. PassManager<Function> is not affected, because it is referenced in libLLVMCore.a outside the .o file that contains the explicit instantiation, while PassManager<Loop> *is* affected, because it is referenced in libLLVMAnalysis.a outside the .o file that contains the explicit instantiation, but that .cpp file including the reference does *not* include LoopPassManager.h where the template instantiation is declared extern. This somehow causes the linker to treat the two cases differently.