Steve Lorimer Steve Lorimer - 3 months ago 25
C++ Question

How to configure CMake to build a library with -fPIC?

I'm trying to create a static library with

-fPIC
specified.

add_library(cpp-netlib_pic
STATIC
${SRCS})
set_property(TARGET cpp-netlib_pic PROPERTY POSITION_INDEPENDENT_CODE)


This doesn't work.

The library (
cpp-netlib_pic
) is built without the
-fPIC
flags.

Other targets which link against
cpp-netlib_pic

do however, have
-fPIC
added to their compiler flags, but the linking fails because
cpp-netlib_pic
didn't.

Here
foo
will have
-fPIC
added:

add_library(foo
SHARED
${SRCS})
target_link_libraries(foo cpp-netlib_pic)


I've proved this to myself with make VERBOSE=1

[ 87%] Building CXX object third_party/cpp-netlib/CMakeFiles/cpp-netlib_pic.dir/src/server_request_parsers_impl.cpp.o
/usr/bin/c++ ... -std=c++14 -Werror -Wall -Wextra ... \
-o CMakeFiles/cpp-netlib_pic.dir/src/server_request_parsers_impl.cpp.o \
-c .../third_party/cpp-netlib/src/server_request_parsers_impl.cpp


Note no
-fPIC
here.

When building target
foo
which uses
cpp-netlib_pic
,
-fPIC
appears:

[ 93%] Building CXX object foo.cc.o
/usr/bin/c++ ... -std=c++14 -Werror -Wall -Wextra ... -fPIC ... \
-o CMakeFiles/foo_shared_lib.dir/foo.cc.o \
-c .../foo/foo.cc


How can I configure CMake to build the 1st library (
cpp-netlib_pic
) with
-fPIC
?

Answer

You seem to have forgotten the ON:

set_property(TARGET cpp-netlib_pic PROPERTY POSITION_INDEPENDENT_CODE ON)