Did upgrading to Ubuntu 14.04 break the c++ linker? - c++

Question

I have a Linux-based application, running under Ubuntu 12.04 LTS, that compiled, linked, and ran with no problem.
I recently upgraded my Ubuntu to 14.04 LTS and encountered problems compiling and linking the app.
The compilation problems were solved by manually modifying my local copy of Boost 1.48 in two files (include/boost/config/stdlib/libstdcpp3.hpp and include/boost/thread/xtime.hpp). At this point the app compiled successfully.
The problem I have is that the linkage fails with the error message:
c++: error: unrecognized command line option ‘-Wl’
I use CMake to enable compiling the app on multiple platforms. Here is the linker script generated by CMake. Note that the "-Wl" options are now inexplicably unrecognized by /usr/bin/c++:
/usr/bin/c++
-fno-stack-protector
-g
-Wl
CMakeFiles/Project.dir/main.cpp.o
CMakeFiles/Project.dir/TestCallback.cpp.o
CMakeFiles/Project.dir/utils.cpp.o
CMakeFiles/Project.dir/Request1.cpp.o
CMakeFiles/Project.dir/Response1.cpp.o
CMakeFiles/Project.dir/TextChatRequest.cpp.o
CMakeFiles/Project.dir/TextChatResponse.cpp.o
-o
/home/user/private/Project/Project_Release_1_2_Codename/Build/bin/Debug/Project
-L/home/user/Libraries/Ubuntu32_12.04/boost_1.48/lib
-L/home/user/Libraries/Ubuntu32_12.04/SqlLite_3.6/lib
-L/home/user/Libraries/Ubuntu32_12.04/taglib_1.7/lib
-L/home/user/Libraries/Ubuntu32_12.04/JSON_1.0/lib/Debug
-L/home/user/private/Project/Project_Release_1_2_Codename/Build/../lib/libUbuntu32/Debug
-rdynamic
/home/user/private/Project/Project_Release_1_2_Codename/lib/libUbuntu32/Debug/libAPI.a
/home/user/private/Project/Project_Release_1_2_Codename/lib/libUbuntu32/Debug/libInternals.a
-lboost_thread
-lboost_system
-lboost_filesystem
-lboost_program_options
-ltaglib
-lJSON
-lpthread
-Wl,-Bstatic
-lsqlite3
-Wl,-Bdynamic
-ldl
-Wl,-rpath,/home/user/Libraries/Ubuntu32_12.04/boost_1.48/lib:/home/user/Libraries/Ubuntu32_12.04/SqlLite_3.6/lib:/home/user/Libraries/Ubuntu32_12.04/taglib_1.7/lib:/home/user/Libraries/Ubuntu32_12.04/JSON_1.0/lib/Debug:/home/user/private/Project/Project_Release_1_2_Codename/Build/../lib/libUbuntu32/Debug
Here is version information for the software I'm using:
Ubuntu:
14.04.1 LTS (trusty)
c++ compiler/linker:
(Ubuntu 4.8.2-19ubuntu1) 4.8.2
CMake:
Version 2.8.12.2
Why doesn't the linker recognize "-Wl" commands? Did my upgrade to 14.04 LTS modify the linker software libraries? How can I get my app back up and linking?

Answer 1

On line 4 of the command you have -Wl without any actual linker options.
https://gcc.gnu.org/gcc-4.7/porting_to.html
Right at the top of this page is the following:
Earlier releases did not warn or error about completely invalid
options on gcc/g++/gfortran etc. command lines, if nothing was
compiled, but only linking was performed. This is no longer the case.
For example,
gcc -Wl -o foo foo.o -mflat_namespace
Now produces the following error
error: unrecognized command line option ‘-Wl’
error: unrecognized command line option ‘-mflat_namespace’
Invalid options need to be removed from the command line or replaced by something that is valid.
12.04 LTS packaged GCC 4.6, you've now jumped to 4.8 and -Wl on its own is no longer a valid option (or rather it never was, GCC is just more pedantic now).

Answer 2

As mentioned by others previously, it indeed turned out that my CMake script was injecting a lone, solitary, seemingly unnecessary "-Wl" via the CMAKE_EXE_LINKER_FLAGS setting:
if(LINUX)
set(THIRDPARTY_LIBS boost_thread boost_system boost_filesystem boost_program_options taglib JSON)
set(OS_LIBS pthread sqlite3.a dl)
set(CMAKE_EXE_LINKER_FLAGS "-Wl")
set(PREPROCESSOR_DEFINITIONS ${PREPROCESSOR_DEFINITIONS};/DTAGLIB_STATIC)
endif(LINUX)
When I removed this setting, the build succeeded. This oversight has been around a while, with the earlier version of gcc not minding. The latest gcc, however, is more pedantic and flagged it as an error.