emscripten Linking globals named symbol multiply defined - c++

Question

I have a c++ CMAKE (VERSION 3.10.2 -std=c++17 ) project that i am able to compile and link with bought gcc and clang. Bought of them produce the target binaries which work as expected. Recently i decided to to try and add another target i.e. webassembly. The project is compiling as expect, however when the EMscripten build is being executed i.e. in the linking phase i get the following error:
Elapsed time: 1 s. (time), 0.002241 s. (clock)
[100%] Linking CXX executable wasmExec.js
cd /Projects/time/time.cpp/build/src/wasm && /usr/bin/cmake -E cmake_link_script CMakeFiles/wasmExec.dir/link.txt --verbose=1
/Projects/emscripten/emsdk/emscripten/1.38.12/em++ -s WASM=1 -s NO_EXIT_RUNTIME=1 -s VERBOSE=1 --pre-js /Projects/time/time.cpp/src/wasm/preModule.js -s DEMANGLE_SUPPORT=1 -s DISABLE_EXCEPTION_CATCHING=0 -s ERROR_ON_UNDEFINED_SYMBOLS=0 #CMakeFiles/wasmExec.dir/objects1.rsp -o wasmExec.js #CMakeFiles/wasmExec.dir/linklibs.rsp
error: Linking globals named '_ZTVN9timeproto3time8defaults20TimeDefaultParametersE': symbol multiply defined!
WARNING:root:Note: Input file "#/tmp/tmpUeJ6zc.response" did not exist.
ERROR:root:Failed to run llvm optimizations:
When i do
c++filt _ZTVN9timeproto3time8defaults20TimeDefaultParametersE
i get
vtable for timeproto::time::defaults::TimeDefaultParameters
from another answer by Stackoverflow i.e.
Possible reasons for symbol multiply defined other than 'extern'
i do understand that i have defined this class more then once, however my problem is that i can not locate that place where i have made the mistake with the second definition. In the previous answer the person had the hint i.e. the cpp file where that he has made that mistake but in my case emscipten is not so generous.
This class is used all over the code base in many many files and after long manual searching i was not able to find anything that can point me at least to the localtion of the second definition. Thus i was hoping that someone can help me with the following questions
1) how can this be troubleshoot further in order to find where exactly the second defintion of the class is occuring, maybe a flag by gcc or clang ?
2) why this error is beeing displayed only when I am trying to compile/build the webassmbly target. The regular Linux64 build target is successefull and the test are also working correctly.
3) I am running cmake with following "add_definitions" i.e.
if(UNIX)
add_definitions(" -pedantic -pedantic-errors -W ")
add_definitions(" -Wall -Wextra -Werror -Wshadow -Wnon-virtual-dtor ")
add_definitions(" -v ")
# add_definitions(" -Worl-style-cast -Wcast-align ")
# add_definitions(" -Wunused -Woverloaded-virtual ")
add_definitions(" -g ")
endif(UNIX)
if the TimeDefaultParameters has been defined more then once should't clang not complain also for linux build with the above "add_definitions" ?
here is the code below TimeDefaultParameters.cpp This is a very simple file that does not contain any object instead it has 43 "static const uint32_t" variables.
#include "TimeDefaultParameters.h"
namespace timeproto::time::defaults
{
TimeDefaultParameters::TimeDefaultParameters() {
}
TimeDefaultParameters::~TimeDefaultParameters() {
}
const uint32_t TimeDefaultParameters::SIGNED_SHORT_MAX_VALUE = 32767;
.... (another 42 static const uint32_t)
}
and the header file TimeDefaultParameters.h:
#ifndef _TIME_DEFAULT_PARAMETERS_
#define _TIME_DEFAULT_PARAMETERS_
#include <stdint.h>
namespace timeproto::time::defaults
{
class TimeDefaultParameters final
{
public:
explicit TimeDefaultParameters();
virtual ~TimeDefaultParameters();
static const uint32_t SIGNED_SHORT_MAX_VALUE;
.....
.... (another 42 static const uint32_t)
};
}
#endif //#ifndef _TIME_DEFAULT_PARAMETERS_
in cmake i have the set my target properties like:
set_target_properties(wasmExec PROPERTIES LINK_FLAGS "-s WASM=1 -s NO_EXIT_RUNTIME=1 -s VERBOSE=1 --pre-js /Projects/time/time.cpp/src/wasm/preModule.js -s DEMANGLE_SUPPORT=1 -s DISABLE_EXCEPTION_CATCHING=0 -s ERROR_ON_UNDEFINED_SYMBOLS=0" )
this is how i am calling cmake to make the build from withing the build directory
emconfigure cmake -DCMAKE_BUILD_TYPE=Emscripten -G "Unix Makefiles" -DCMAKE_TOOLCHAIN_FILE=/Projects/emscripten/emsdk/emscripten/1.38.12/cmake/Modules/Platform/Emscripten.cmake ../
make -j8
any ideas are greatly appreciated.
ADDITION: 05 January 2020
I was able to find a workaround for this problem but i still it leaves some questions of the nature of the error.
The class in question was part of the archive that was created and loaded dynamically i.e. i had used in the CMAKE part for this library "set(LIB_TYPE SHARED)".
here is full example how cmake generated that archive i.e. the CMakeLists.txt.
set( TIME_DEFAULTS_SRC
...
TimeDefaultParameters.h TimeDefaultParameters.cpp
...
)
set(LIB_TYPE STATIC)
#set(LIB_TYPE SHARED)
add_library(time_defaults ${LIB_TYPE} ${TIME_DEFAULTS_SRC} )
target_include_directories(time_defaults PUBLIC "${CMAKE_CURRENT_SOURCE_DIR}/")
I have changed from dynamic to static and i was able to create the wasm no errors were shown. During the compilation i also saw somewhere in between of the compilation process some warrning i.e. :
WARNING:root:When Emscripten compiles to a typical native suffix for shared libraries (.so, .dylib, .dll) then it emits an LLVM bitcode file. You should then compile that to an emscripten SIDE_MODULE (using that flag) with suffix .wasm (for wasm) or .js (for asm.js). (You may also want to adapt your build system to emit the more standard suffix for a file with LLVM bitcode, '.bc', which would avoid this warning.)
this warrning is now gone. But it is very easy to oversee thing like that especially if the compilation process is taking long time. However my understanding is that the very first error message tells us , "look you have made duplicate definition of some symbol in your code go find the place and make sure that the class is define only once". That was exactly what i was doing i.e. searching the code base for that duplicate definition. Thus now the question is: Why emscripten have a problem does with dynamic linking i.e. i know that it is officially supported i.e.
https://webassembly.org/docs/dynamic-linking/
and is that the source of the error at all or is something else?
Why this error disappears when i change to static. I can reproduce this by simply changing library type!
I think i already found the answer here
https://github.com/emscripten-core/emscripten/wiki/Linking

Answer 1

So the solution in my case was to find the occurrences in the CMAKE file where the library was added dynamically and change that to static linking i.e.
#set(LIB_TYPE SHARED)
set(LIB_TYPE STATIC)