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

[Rafael Espíndola via llvm-dev]

This probably just works around a layering violation. Can you provide the
cmake line that produces a broken build?

Cheers,
Rafael
On Jun 18, 2016 7:34 AM, "Nicolai Hähnle" <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.

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.

Thanks,
Nicolai
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