My meson.build constructs an erroneous c++ or ld command: some error about -fPIC, what's it mean and how to rectify?

[metaleap]

Lemme share the error message at hand first, during a meson.compile:

INFO: autodetecting backend as ninja
INFO: calculating backend command to run: /usr/bin/ninja -C /home/_/c/c/mo25/build
ninja: Entering directory `/home/_/c/c/mo25/build'
[2/4] Linking target libmo_gfx.so
FAILED: libmo_gfx.so 
c++  -o libmo_gfx.so libmo_gfx.so.p/mo_gfx_mo_gfx.cpp.o -Wl,--as-needed -Wl,--no-undefined -shared -fPIC -Wl,-soname,libmo_gfx.so -pthread -Wl,--start-group /usr/lib/libSDL2-2.0.so.0.3000.10 /usr/lib/libSDL2main.a /usr/local/lib/WickedEngine/libFAudio.a /usr/local/lib/WickedEngine/libJolt.a /usr/local/lib/WickedEngine/libLUA.a /usr/local/lib/WickedEngine/libUtility.a /usr/local/lib/WickedEngine/libWickedEngine_Linux.a -Wl,--end-group
/usr/bin/ld: /usr/local/lib/WickedEngine/libWickedEngine_Linux.a(wiFont.cpp.o): relocation R_X86_64_TPOFF32 against `__tls_guard' can not be used when making a shared object; recompile with -fPIC
/usr/bin/ld: failed to set dynamic section sizes: bad value
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.

It's just this very-tiny minimal project for now, here's the meson.build:

project('mo', ['cpp', 'c'])
dep_wicked = dependency('WickedEngine', static: true)
lib_gfx = library('mo_gfx', sources: ['mo_gfx/mo_gfx.cpp'], dependencies: [dep_wicked])
executable('mo.exec', sources: ['main.cpp'], link_with: [lib_gfx])

The main.cpp:

#include "mo_gfx/mo_gfx.h"
int main(int argc, char** argv) {
  moStart();
  return 0;
}

The mo_gfx.cpp:

#include <stdio.h>
#include <WickedEngine/WickedEngine.h>
void moStart() {
  printf("HolaMain\n");
}

So this happens from just the #include <WickedEngine/WickedEngine.h> — not even using it.

(What's this WickedEngine? Exists in my /usr/local/lib and /usr/local/include. I first built it via this CMakeLists.txt ie: cmake and then make and then make install. It's not supposed to be a subproject or a directory in my project. And I don't wanna tweak its own build setup as I'll occasionally update that lib.)

[eli-schwartz]

/usr/local/lib/WickedEngine/libWickedEngine_Linux.a(wiFont.cpp.o)

This file is built without support for using in a shared library. Shared libraries require PIC. Static libraries can optionally use PIC, but if they don't use PIC then you can only link them into executables, not into shared libraries.

There are security considerations that suggest using PIC for all code, even code intended for static linking into a binary, and also modest performance penalties for doing so (32-bit systems). Many people simply compile all objects with PIC and save themselves a lot of trouble.

There's nothing meson can do about this -- the cmake-built static library was compiled with options that don't support using it in a shared library. You need to recompile.

FWIW, meson defaults to PIC on static libraries but provides a global meson-level option "b_staticpic" for people who know their static libraries will only be used by executables (never shared libraries), and would prefer the slight speed bonus and corresponding security tradeoff.

[dcbaker]

CMake has a builtin in for this as well, but it defaults to OFF, setting CMAKE_POSITION_INDEPENDENT_CODE to ON in the wicked build will fix this.

[metaleap]

Thanks so much for the informative instructive explanation! Much appreciated. Will try a Wicked build with -DCMAKE_POSITION_INDEPENDENT_CODE=ON first; if failure, will change my mo_gfx lib to static_library..