relocation R_X86_64_PC32 against symbol _ZTISt13runtime_error@@GLIBCXX_3.4 can not be used when making a shared object; recompile with -fPIC

Question

The project I am attempting compile is not in any way complex, and references nothing but the standard library and one self-contained library (everything compiles fine on another system). As indicated by the title, it can't even link against something in the standard library, due to things in there not having been compiled with -fPIC, supposedly. I didn't build it myself, nor do I want to, and reinstalling things with apt didn't seem to resolve the "recompile with -fPIC" issue.

I will say that I think one possible source of the issue is due to gcc-multilib or something being installed earlier, but I think that was purged. I don't know, maybe something was overwritten or a conflict arose. Might not even be related. Any ideas?

Running Ubuntu 18.04

g++ -I inc -I /usr/include/mono-2.0 -MMD -MF dep/Nonsense.d -std=c++17 -O3 -fno-stack-protector -fno-unroll-loops -fomit-frame-pointer -Wno-ignored-optimization-argument -c -o obj/Nonsense.o src/Nonsense.cpp
g++ -I inc -I /usr/include/mono-2.0 -MMD -MF dep/Socket.d -std=c++17 -O3 -fno-stack-protector -fno-unroll-loops -fomit-frame-pointer -Wno-ignored-optimization-argument -c -o obj/Socket.o src/Socket.cpp
g++ -shared -flto -o libNonsense.so obj/Nonsense.o obj/Socket.o -Llib -lenet
/usr/bin/x86_64-linux-gnu-ld: obj/Socket.o: relocation R_X86_64_PC32 against symbol `_ZTISt13runtime_error@@GLIBCXX_3.4' can not be used when making a shared object; recompile with -fPIC
/usr/bin/x86_64-linux-gnu-ld: final link failed: Bad value
collect2: error: ld returned 1 exit status
makefile:22: recipe for target 'libNonsense.so' failed
make: *** [libNonsense.so] Error 1

Answer 1

As the error message says, you need to recompile with -fPIC. Your current compiler command does not show the -fPIC option:

g++ -I inc -I /usr/include/mono-2.0 -MMD -MF dep/Socket.d -std=c++17 -O3 -fno-stack-protector -fno-unroll-loops -fomit-frame-pointer -Wno-ignored-optimization-argument -c -o obj/Socket.o src/Socket.cpp

Same for -flto by the way—this flag also has to be specified when compiling in order to be effective.

Answer 2

Apparently, it is compulsory to compile with the -fPIC flag in 64bits platform. If you are making a 32-bits project with linkink with 32-bits library; you don't need -fPIC. Indeed, without -fPIC, the dynamic linker recalculates adresses for global variables and functions (which are not known in advance in the step of compilation). However, in a 64-bits system, it is not possible to use this technique as it is required to guess in advance the size of adress. PIC (Position Independent Code), a more sophisticated and complicated process is used. https://eli.thegreenplace.net/2011/11/11/position-independent-code-pic-in-shared-libraries-on-x64 for explanations.