Abseil with CMake in a library

Question

I'm writing a library that uses CMake and trying to get Abseil linked into it following the instructions here:

https://github.com/abseil/abseil-cpp/blob/master/CMake/README.md

My CMakeLists.txt basically contains:

add_library(MyLib SHARED src/mylib.cc)
add_subdirectory(third_party/abseil-cpp)
target_link_libraries(MyLib PRIVATE absl::base absl::strings absl::str_format)

Now if I compile my library, I get the following error:

/usr/bin/ld: third_party/abseil-cpp/absl/strings/libabsl_absl_str_format_internal.a(arg.cc.o): relocation R_X86_64_PC32 against symbol `_ZNKSt17basic_string_viewIcSt11char_traitsIcEE4sizeEv' can not be used when making a shared object; recompile with -fPIC

In other words, CMake compiles Abseil without using position independent code. I then tried for fun to see what happens if I change my library to be a static one instead. Changing CMakeLists.txt to

add_library(MyLib STATIC src/mylib.cc)
add_subdirectory(third_party/abseil-cpp)
target_link_libraries(MyLib PRIVATE absl::base absl::strings absl::str_format)

I get the following error when running cmake:

CMake Error: install(EXPORT "MyLibTargets" ...) includes target "MyLib" which requires target "absl_base" that is not in the export set.
CMake Error: install(EXPORT "MyLibTargets" ...) includes target "MyLib" which requires target "absl_strings" that is not in the export set.
CMake Error: install(EXPORT "MyLibTargets" ...) includes target "MyLib" which requires target "absl_str_format" that is not in the export set.

I'm a CMake newbie and I haven't managed to figure out how to fix either error. How can you transitively in CMake specify that dependencies should compile to position independent code?

score 1 · Answer 1 · answered Nov 21 '19 at 14:24

From this thread on GitHub:

Looks like you want to use CMAKE_POSITION_INDEPENDENT_CODE as suggested by @Mizux earlier. Add set(CMAKE_POSITION_INDEPENDENT_CODE TRUE) to your CMakeLists.txt file [...]

This should fix any issues you see while building a shared library, while still building and linking abseil into your library statically.

Abseil with CMake in a library

1 Answers1